DXA Reporting Updates: 2023 Official Positions of the International Society for Clinical Densitometry

INTRODUCTION

Professional guidance and standards assist radiologic interpreters in generating high quality reports. Initially DXA reporting Official Positions were provided by the ISCD in 2003; however, as the field has progressed, some of the current recommendations require revision and updating. This manuscript details the research approach and provides updated DXA reporting guidance.

METHODS

Key Questions were proposed by ISCD established protocols and approved by the Position Development Conference Steering Committee. Literature related to each question was accumulated by searching PubMed, and existing guidelines from other organizations were extracted from websites. Modifications and additions to the ISCD Official Positions were determined by an expert panel after reviewing the Task Force proposals and position papers.

RESULTS

Since most DXA is now performed in radiology departments, an approach was endorsed that better aligns with standard radiologic reports. To achieve this, reporting elements were divided into required minimum or optional. Collectively, required components comprise a standard diagnostic report and are considered the minimum necessary to generate an acceptable report. Additional elements were retained and categorized as optional. These optional components were considered relevant but tailored to a consultative, clinically oriented report. Although this information is beneficial, not all interpreters have access to sufficient clinical information, or may not have the clinical expertise to expand beyond a diagnostic report. Consequently, these are not required for an acceptable report.

CONCLUSION

These updated ISCD positions conform with the DXA field's evolution over the past 20 years. Specifically, a basic diagnostic report better aligns with radiology standards, and additional elements (which are valued by treating clinicians) remain acceptable but are optional and not required. Additionally, reporting guidance for newer elements such as fracture risk assessment are incorporated. It is our expectation that these updated Official Positions will improve compliance with required standards and generate high quality DXA reports that are valuable to the recipient clinician and contribute to best patient care.

Effect of Positioning of the Region of Interest on Bone Density of the Hip

BACKGROUND

Large changes in positioning of the global region of interest (ROI) influence the measurement of bone mineral density (BMD) in the hip and forearm regions. However, it is unknown whether minor shifts in the positioning of the bottom of the global hip ROI affect the measurement of total hip BMD.

METHODS

The hip BMDs of 40 clinical densitometry patients were analyzed at baseline with the bottom of the global hip ROI positioned as usual, 10 mm distal to the base of the lesser trochanter (position 0). Then the hip was reanalyzed by shifting the bottom of the global hip ROI 1 mm proximally 10 times (positions +1 through +10) and then by shifting the bottom of the global hip ROI 1 mm distally 10 times (positions -1 through -10). The significance of the differences between mean values at the various distances from baseline was assessed using a Wilcoxon signed-rank test.

RESULTS

The mean total hip area, bone mineral content and BMD decreased as the bottom of the global hip ROI was shifted proximally; the decrease was significant when shifted by even 1 mm (p < 0.001). The mean total hip area, bone mineral content and BMD increased as the bottom of the global hip ROI was shifted distally; the increase was significant when shifted by even 1 mm (p < 0.001). The change in BMD with each 1 mm shift was uniform across the range studied from positions +10 through -10, and was approx 0.54%/mm. When the least significant change was based on 40 pairs of measurements, where each pair was comprised of the baseline scan and the same scan at -1 position, the least significant change was 0.01 g/cm².

CONCLUSIONS

The BMD of the total hip is sensitive to even minor changes in the positioning of the bottom of the global hip ROI. Although a 1 mm change in the bottom of the global hip ROI positioning would make little difference in the reported T-score, it could easily affect the determination of significance in changes in BMD over time.

Executive Summary of the 2019 ISCD Position Development Conference on Monitoring Treatment, DXA Cross-calibration and Least Significant Change, Spinal Cord Injury, Peri-prosthetic and Orthopedic Bone Health, Transgender Medicine, and Pediatrics

To answer important questions in the fields of monitoring with densitometry, dual-energy X-ray absorptiometry machine cross-calibration, monitoring, spinal cord injury, periprosthetic and orthopedic bone health, transgender medicine, and pediatric bone health, the International Society for Clinical Densitometry (ISCD) held a Position Development Conference from March 20 to 23, 2019. Potential topics requiring guidance were solicited from ISCD members in 2017. Following that, a steering committee selected, prioritized, and grouped topics into Task Forces. Chairs for each Task Force were appointed and the members were co-opted from suggestions by the Steering Committee and Task Force Chairs. The Task Forces developed key questions, performed literature searches, and came up with proposed initial positions with substantiating draft publications, with support from the Steering Committee. An invited Panel of Experts first performed a review of draft positions using a modified RAND Appropriateness Method with voting for appropriateness. Draft positions deemed appropriate were further edited and presented at the Position Development Conference meeting in an open forum. A second round of voting occurred after discussions to approve or reject the positions. Finally, a face-to-face closed session with experts and Task Force Chairs, and subsequent electronic follow-up resulted in 34 Official Positions of the ISCD approved by the ISCD Board on May 28, 2019. The Official Positions and the supporting evidence were submitted for publication on July 1, 2019. This paper provides a summary of the all the ISCD Adult and Pediatric Official Positions, with the new 2019 positions highlighted in bold.

Bone Densitometry in Transgender and Gender Non-Conforming (TGNC) Individuals: 2019 ISCD Official Position

The indications for initial and follow-up bone mineral density (BMD) in transgender and gender nonconforming (TGNC) individuals are poorly defined, and the choice of which gender database to use to calculate Z-scores is unclear. Herein, the findings of the Task Force are presented after a detailed review of the literature. As long as a TGNC individual is on standard gender-affirming hormone treatment, BMD should remain stable to increasing, so there is no indication to monitor for bone loss or osteoporosis strictly on the basis of TGNC status. TGNC individuals who experience substantial periods of hypogonadism (>1 yr) might experience bone loss or failure of bone accrual during that time, and should be considered for baseline measurement of BMD. To the extent that this hypogonadism continues over time, follow-up measurements can be appropriate. TGNC individuals who have adequate levels of endogenous or exogenous sex steroids can, of course, suffer from other illnesses that can cause osteoporosis and bone loss, such as hyperparathyroidism and steroid use; they should have measurement of BMD as would be done in the cisgender population. There are no data that TGNC individuals have a fracture risk different from that of cisgender individuals, nor any data to suggest that BMD predicts their fracture risk less well than in the cisgender population. The Z-score in transgender individuals should be calculated using the reference data (mean and standard deviation) of the gender conforming with the individual's gender identity. In gender nonconforming individuals, the reference data for the sex recorded at birth should be used. If the referring provider or the individual requests, a set of "male" and "female" Z-scores can be provided, calculating the Z-score against male and female reference data, respectively.

BMI, Waist Circumference, and Risk of Incident Vertebral Fracture in Women

OBJECTIVE

The study aimed to investigate the association between BMI, waist circumference, and vertebral fracture (VF) risk in women.

METHODS

This prospective study was conducted in 54,934 Nurses' Health Study participants. BMI was assessed biennially, and waist circumference was assessed in the year 2000. Self-reports of VF were confirmed by record review. BMI reflects lean body mass, and waist circumference reflects abdominal adiposity when included in the same regression model.

RESULTS

This study included 536 VF cases (2002 to 2014). Compared with women with BMI of 21.0 to 24.9 kg/m² , the multivariable-adjusted relative risk (RR) of VF for women with BMI ≥ 32.0 was 0.84 (95% CI: 0.61-1.14; P_trend  = 0.08). After further adjustment for waist circumference, the multivariable-adjusted RR of VF for women with BMI ≥ 32.0 was 0.70 (95% CI: 0.49-0.98; P_trend  = 0.003). Compared with women with waist circumference < 71.0 cm, the multivariable-adjusted RR of VF for women with waist circumference ≥ 108.0 cm was 1.76 (95% CI: 1.06-2.92; P_trend  = 0.01), and after further adjustment for BMI, the multivariable-adjusted RR of VF was 2.49 (95% CI: 1.44-4.33; P_trend  < 0.001).

CONCLUSIONS

Greater lean body mass was independently associated with lower VF risk. Larger waist circumference was independently associated with higher VF risk. These findings suggest that fat distribution is an important predictor of VF and that avoiding central adiposity, as well as maintaining muscle mass, may potentially confer reduced risk of VF in older women.

Proton Pump Inhibitor Use, H2-Receptor Antagonist Use, and Risk of Incident Clinical Vertebral Fracture in Women

The few prospective studies examining the relation between proton pump inhibitor (PPI) use and risk of vertebral fracture (VF) suggest a higher risk, but the magnitude of the association has been inconsistent. Moreover, no prospective studies have examined the association between substantially longer duration of PPI use and VF risk. Our objective was to determine the association between PPI use, H₂RA use, and incident clinical VF in women. We conducted a prospective study in 55,545 women participating in the Nurses' Health Study. PPI and H₂RA use was assessed by questionnaire every 4 years. Self-reports of VF were confirmed by medical record. Our analysis included 547 incident VF cases (2002-2014). The multivariate adjusted relative risk (MVRR) of VF for women taking PPIs was 1.29 (95% CI 1.04-1.59) compared with non-users. Longer duration of PPI use was associated with higher VF risk (MVRR 1.16 [0.90-1.49] for < 4 years; 1.27 [0.93-1.73] for 4-7.9 years; 1.64 [1.02-2.64] for ≥ 8 years; p_trend = 0.01). The MVRR of VF for women taking H₂RAs was 1.22 (0.90-1.67) compared with non-users. Longer duration of H₂RA use was not associated with VF risk (MVRR 1.16 [0.88-1.53] for < 4 years; 0.98 [0.60-1.59] for ≥ 4 years; p_trend = 0.72). PPI use is independently associated with a modestly higher risk of VF and the risk increases with longer duration of use. There was no statistically significant association between H₂RA use and VF risk. Our findings add to the growing evidence suggesting caution with PPI use, particularly with longer duration of use.

Direct Comparison of the Precision of the New Hologic Horizon Model With the Old Discovery Model

Previous publications suggested that the precision of the new Hologic Horizon densitometer might be better than that of the previous Discovery model, but these observations were confounded by not using the same participants and technologists on both densitometers. We sought to study this issue methodically by measuring in vivo precision in both densitometers using the same patients and technologists. Precision studies for the Horizon and Discovery models were done by acquiring spine, hip, and forearm bone mineral density twice on 30 participants. The set of 4 scans on each participant (2 on the Discovery, 2 on the Horizon) was acquired by the same technologist using the same scanning mode. The pairs of data were used to calculate the least significant change according to the International Society for Clinical Densitometry guidelines. The significance of the difference between least significant changes was assessed using a Wilcoxon signed-rank test of the difference between the mean square error of the absolute value of the differences between paired measurements on the Discovery (Δ-Discovery) and the mean square error of the absolute value of the differences between paired measurements on the Horizon (Δ-Horizon). At virtually all anatomic sites, there was a nonsignificant trend for the precision to be better for the Horizon than for the Discovery. As more vertebrae were excluded from analysis, the precision deteriorated on both densitometers. The precision between densitometers was almost identical when reporting only 1 vertebral body. (1) There was a nonsignificant trend for greater precision on the new Hologic Horizon compared with the older Discovery model. (2) The difference in precision of the spine bone mineral density between the Horizon and the Discovery models decreases as fewer vertebrae are included. (3) These findings are substantially similar to previously published results which had not controlled as well for confounding from using different subjects and technologists.

Effect of Positioning of the ROI on BMD of the Forearm and Its Subregions

Inconsistent positioning of patients and region of interest (ROI) is known to influence the precision of bone mineral density (BMD) measurements in the spine and hip. However, it is unknown whether minor shifts in the positioning of the ROI along the shaft of the radius affect the measurement of forearm BMD and its subregions. The ultradistal (UD-), mid-, one-third, and total radius BMDs of 50 consecutive clinical densitometry patients were acquired. At baseline the distal end of the ROI was placed at the tip of the ulnar styloid as usual, and then the forearm was reanalyzed 10 more times, each time shifting the ROI 1 mm proximally. No corrections for multiple comparisons were necessary since the differences that were significant were significant at p < 0.001. The UD-radius BMD increased as the ROI was shifted proximally; the increase was significant when shifted even 1 mm proximally (p < 0.001). These same findings held true for the mid- and total radius bone density, though the percent increase with moving proximally was significantly greater for the UD radius than for the other subregions. However, there was no significant change in the one-third radius BMD when shifted proximally 1-10 mm. Minor proximal shifts of the forearm ROI substantially affect the BMD of the UD-, mid- and total radius, while having no effect on the one-third radius BMD. Since the one-third radius is the only forearm region usually reported, minor proximal shifts of the ROI should not influence forearm BMD results significantly.

A meta-analysis of the association between body mass index and risk of vertebral fracture

We conducted a meta-analysis of prospective studies to assess the association between BMI and incident vertebral fracture. We found that as body mass index (BMI) increases, the risk of vertebral fracture decreases in men, but not in women, suggesting possible gender differences in the relationship of BMI with risk of vertebral fracture.

INTRODUCTION

Recent evidence suggests that the relationship between BMI and fracture risk may be site-specific. We conducted a systematic review and meta-analysis of prospective studies to investigate the association between BMI and risk of incident vertebral fracture.

METHODS

PubMed and Embase were searched for relevant articles published from inception through February 15, 2017. Extracted relative risks (RR) from the prospective studies were pooled using random-effects meta-analysis.

RESULTS

Six studies were included, with a total of 105,129 participants followed for 3 to 19 years. The pooled RR (95% confidence interval [CI]) for vertebral fracture per each standard deviation increase in BMI was 0.94 (95% CI = 0.80-1.10) with significant heterogeneity (I ² = 88.0%, p < 0.001). In subgroup analysis by gender, we found a significant inverse association between BMI and risk of vertebral fracture in men (RR = 0.85, 95% CI = 0.73-0.98, n = 25,617 participants) but not in women (RR = 0.98, 95% CI = 0.81-1.20, n = 79,512 participants). Across studies of women not adjusting for bone mineral density (BMD), there was no significant association between BMI and risk of vertebral fracture (RR = 0.91, 95% CI = 0.80-1.04, p = 0.18, n = 72,755 participants). However, BMI was associated with an increased risk of vertebral fracture in studies of women that adjusted for BMD (RR = 1.28, 95% CI = 1.17-1.40, p < 0.001, n = 6757 participants). Substantial heterogeneity was found among studies of women (I ² = 90.1%, p < 0.001), which was partly explained by the adjustment for BMD (adjusted R ² = 61%). We found no evidence of publication bias (p = 0.40).

CONCLUSIONS

In conclusion, our findings suggest that there might be gender differences in the relationship of BMI with risk of vertebral fracture. Further research is needed, including the assessment of other measures of adiposity, such as visceral adiposity, on the risk of vertebral fracture.

Enhanced Precision of the New Hologic Horizon Model Compared With the Old Discovery Model Is Less Evident When Fewer Vertebrae Are Included in the Analysis

The International Society for Clinical Densitometry guidelines recommend using locally derived precision data for spine bone mineral densities (BMDs), but do not specify whether data derived from L1-L4 spines correctly reflect the precision for spines reporting fewer than 4 vertebrae. Our experience suggested that the decrease in precision with successively fewer vertebrae is progressive as more vertebrae are excluded and that the precision for the newer Horizon Hologic model might be better than that for the previous model, and we sought to quantify. Precision studies were performed on Hologic densitometers by acquiring spine BMD in fast array mode twice on 30 patients, according to International Society for Clinical Densitometry guidelines. This was done 10 different times on various Discovery densitometers, and once on a Horizon densitometer. When 1 vertebral body was excluded from analysis, there was no significant deterioration in precision. When 2 vertebrae were excluded, there was a nonsignificant trend to poorer precision, and when 3 vertebrae were excluded, there was significantly worse precision. When 3 or 4 vertebrae were reported, the precision of the spine BMD measurement was significantly better on the Hologic Horizon than on the Discovery, but the difference in precision between densitometers narrowed and was no longer significant when 1 or 2 vertebrae were reported. The results suggest that (1) the measurement of in vivo spine BMD on the new Hologic Horizon densitometer is significantly more precise than on the older Discovery model; (2) the difference in precision between the Horizon and Discovery models decreases as fewer vertebrae are included; (3) the measurement of spine BMD is less precise as more vertebrae are excluded, but still quite reasonable even when only 1 vertebral body is included; and (4) when 3 vertebrae are reported, L1-L4 precision data can reasonably be used to report significance of changes in BMD. When 1 or 2 vertebrae are reported, precision data for 1 or 2 vertebrae, respectively, should be used, because the exclusion of 2-3 vertebrae significantly worsens precision.

Diuretic Use and Risk of Vertebral Fracture in Women

BACKGROUND

Vertebral fracture is the most common type of osteoporotic fracture. While thiazide diuretics, which are commonly prescribed for the treatment of hypertension, decrease calciuria, they may also induce hyponatremia, which has been associated with increased vertebral fracture risk. Loop diuretics increase calciuria, which would reduce bone mineral density and increase vertebral fracture risk, but they rarely cause hyponatremia. Recent studies on diuretics and fractures did not include or specifically examine vertebral fracture. The few studies of diuretics and vertebral fracture have been limited by cases defined by self-report or administrative data, relatively small number of cases, study design that was not prospective, and lack of long-term follow-up with updated information on diuretic use.

METHODS

We conducted a prospective cohort study of thiazide diuretic use, loop diuretic use, and risk of incident clinical vertebral fracture in 55,780 women, 55-82 years of age, participating in the Nurses' Health Study, without a prior history of any fracture. Diuretic use was assessed by questionnaire every 4 years. Self-reported vertebral fracture was confirmed by medical record review. Cox proportional-hazards models were used to simultaneously adjust for potential confounders.

RESULTS

Our analysis included 420 incident vertebral fracture cases documented between 2002 and 2012. The multivariate-adjusted relative risk of clinical vertebral fracture for women taking thiazides compared with women not taking thiazides was 1.47 (95% confidence interval, 1.18-1.85). The multivariate adjusted relative risk of vertebral fracture for women taking loop diuretics compared with women not taking loop diuretics was 1.59 (95% confidence interval, 1.12-2.25).

CONCLUSION

Thiazide diuretics and loop diuretics are each independently associated with increased risk of vertebral fracture in women.

Effect of Clothing on Measurement of Bone Mineral Density

It is unknown whether allowing patients to have BMD (bone mineral density) studies acquired while wearing radiolucent clothing adlib contributes appreciably to the measurement error seen. To examine this question, a spine phantom was scanned 30 times without any clothing, while draped with a gown, and while draped with heavy winter clothing. The effect on mean BMD and on SD (standard deviation) was assessed. The effect of clothing on mean or SD of the area was not significant. The effect of clothing on mean and SD for BMD was small but significant and was around 1.6% for the mean. However, the effect on BMD precision was much more clinically important. Without clothing the spine phantom had an least significant change of 0.0077 gm/cm(2), while when introducing variability of clothing the least significant change rose as high as 0.0305 gm/cm(2). We conclude that, adding clothing to the spine phantom had a small but statistically significant effect on the mean BMD and on variance of the measurement. It is unlikely that the effect on mean BMD has any clinical significance, but the effect on the reproducibility (precision) of the result is likely clinically significant.

Utility of Reviewing Radiology Studies in Electronic Medical Records When Preparing Bone Mineral Density Reports

We quantitated how often review of recent radiology studies provides information useful to the densitometrist. While preparing bone mineral density (BMD) reports on 1012 consecutive patients, radiology reports in electronic medical records (EMRs) for the previous 5 years at potentially relevant sites (lumbar spine X-rays, abdominal computed tomography (CT) scans, and so forth) were reviewed. When a study was found, it received a grade according to how relevant findings were to the BMD report: "1" for studies that were irrelevant, "2" for those that confirmed the impression formed from review of the BMD images, "3" for those that clarified the impression that was unclear after reviewing the BMD images, and "4" for those that revealed new relevant data when no abnormality was noted on review of the BMD images. A total of 562 patients (55.5%) had a radiologic study at a site of potential interest within the past 5 years. Fifty-three patients (5.2% of all patients) had a grade 4 study, 88 patients (8.7% of all patients) had a grade 3 study, and 185 patients (18.3% of all patients) had a grade 2 study. Two hundred sixty-four patients (25.8%) had a grade 2 or 3 study, and 299 (29.5%) had a grade 2-4 study. The radiographic study that was most likely to be found in patients' EMR was chest X-ray (34.7% of all patients), but it was also the one that was least likely to have any relevance to the reader; only 10.5% of the total chest X-rays were graded 2-4. The next most likely studies to be found in patients' EMR were abdominal CT scans (18.0% of all patients) and lumbar spine X-rays (14.4% of all patients), but these studies were much more likely to be useful to the reader, as 62.6% of abdominal CT scans and 78.1% of lumbar spine X-rays were graded 2-4. The likelihood of a patient having radiologic examinations in the EMR at sites potentially relevant to the BMD reader is high, but the likelihood that these clarify abnormalities noted on BMD is only moderate. Review of the EMR is unlikely to be relevant when the dual-energy X-ray absorptiometry images are normal.

Inconsistency in filling in the bottom of the spine bone map affects reported spine bone mineral density

OBJECTIVE

We hypothesized that variability from year to year in how much of the bone map was filled in at the bottom of the spine region of interest (ROI) contributes substantially to variability in measurement of spine bone mineral density (BMD).

METHODS

A total of 110 spine BMDs with defects in the bone mapping at the bottom were reanalyzed, with the only change being manually drawing a straight line across the bottom of the ROI and filling in the bone map.

RESULTS

The mean (SD) change in area, bone mineral content, and BMD for total spine when the bottom of the bone map was filled in was 0.919 (0.411) cm2, 0.201 (0.121) g, and -0.0098 (0.0043) g/cm2, respectively, and all changes were significant (P<.0001). The largest individual change in total spine BMD with reanalysis was 0.0238 g/cm2, close to the least significant change (LSC) of 0.026 g/cm2 in our center. To quantify variability due to this change in analysis, we calculated an LSC(fill), in which the pairs of scans consisted of the same scan before and after filling in the bottom of the spine bone map, without any other change. The LSC(fill) attributable just to the reanalysis of missing bone map at the bottom of the spine was 0.021 g/cm2, suggesting substantial variance due to variability in mapping the bottom of the spine.

CONCLUSION

When there is a noticeable defect in the bottom of the spine bone map, filling this defect in consistently eliminates a significant source of variability in analysis of spine BMDs and might allow us to achieve smaller LSCs.

Indications of DXA in women younger than 65 yr and men younger than 70 yr: the 2013 Official Positions

Dual-energy X-ray absorptiometry (DXA) is the method of choice to assess fracture risk for women 65 yr and older and men 70 yr and older. The 2007 International Society for Clinical Densitometry Official Positions had developed guidelines for assessing bone density in younger women during and after the menopausal transition and in men 50-69 yr and the 2008 National Osteoporosis Foundation (NOF) guidelines recommended testing in postmenopausal women younger than 65 yr and men 50-69 yr only in the presence of clinical risk factors. The purpose of the 2013 DXA Task Force was to reassess the NOF guidelines for ordering DXA in postmenopausal women younger than 65 yr and men 50-69 yr. The Task Force reviewed the literature published since the 2007 Position Development Conference and 2008 NOF, reviewing clinical decision rules such as the Osteoporosis Screening Tool and FRAX and sought to keep recommendations simple to remember and implement. Based on this assessment, the NOF guidelines were endorsed; DXA was recommended in those postmenopausal women younger than 65 yr and men 50-69 yr only in the presence of clinical risk factors for low bone mass, such as low body weight, prior fracture, high-risk medication use, or a disease or condition associated with bone loss.

The Official Positions of the International Society for Clinical Densitometry: vertebral fracture assessment

Vertebral fracture assessment (VFA) is a low-cost method of accurately identifying individuals who have clinically unrecognized or undocumented vertebral fractures at the time of bone density test. Because prevalent vertebral fractures predict subsequent fractures independent of bone mineral density and other clinical risk factors, their recognition is an important part of strategies to identify those who are at high risk of fracture, so that prevention therapies for those individuals can be implemented. The 2007 Position Development Conference developed detailed guidelines regarding the indications for acquisition of, and interpretation and reporting of densitometric VFA tests. The purpose of the 2013 VFA Task Force was to simplify the indications for VFA yet keep them evidence based. The Task Force reviewed the literature published since the 2007 Position Development Conference and developed prediction models based on 2 large cohort studies (the Study of Osteoporotic Fractures and the Osteoporotic Fractures in Men Study) and the densitometry database of the University of Chicago. Based on these prediction models, indications for VFA were reduced to a simplified set of criteria based on age, historical height loss, use of systemic glucocorticoid therapy, and self-reported but undocumented prior vertebral fracture.

Quantification of human and rodent brown adipose tissue function using 99mTc-methoxyisobutylisonitrile SPECT/CT and 18F-FDG PET/CT

For brown adipose tissue (BAT) to be effective at consuming calories, its blood flow must increase enough to provide sufficient fuel to sustain energy expenditure and also transfer the heat created to avoid thermal injury. Here we used a combination of human and rodent models to assess changes in BAT blood flow and glucose utilization.

METHODS

(99m)Tc-methoxyisobutylisonitrile (MIBI) SPECT (n = 7) and SPECT/CT (n = 74) scans done in adult humans for parathyroid imaging were reviewed for uptake in regions consistent with human BAT. Site-directed biopsies of subcutaneous and deep neck fat were obtained for electron microscopy and gene expression profiling. In mice, tissue perfusion was measured with (99m)Tc-MIBI (n = 16) and glucose uptake with (18)F-FDG (n = 16). Animals were kept fasting overnight, anesthetized with pentobarbital, and given intraperitoneally either the β3-adrenergic receptor agonist CL-316,243, 1 mg/kg (n = 8), or saline (n = 8) followed by radiotracer injection 5 min later. After 120 min, the mice were imaged using SPECT/CT or PET/CT. Vital signs were recorded over 30 min during the imaging. BAT, white adipose tissue (WAT), muscle, liver, and heart were resected, and tissue uptake of both (99m)Tc-MIBI and (18)F-FDG was quantified by percentage injected dose per gram of tissue and normalized to total body weight.

RESULTS

In 5.4% of patients (4/74), (99m)Tc-MIBI SPECT/CT showed increased retention in cervical and supraclavicular fat that displayed multilocular lipid droplets, dense capillary investment, and a high concentration of ovoid mitochondria. Expression levels of the tissue-specific uncoupling protein-1 were 180 times higher in BAT than in subcutaneous WAT (P < 0.001). In mice, BAT tissue perfusion increased by 61% (P < 0.01), with no significant changes in blood flow to WAT, muscle, heart, or liver. CL-316,243 increased glucose uptake in BAT even more, by 440% (P < 0.01).

CONCLUSION

Pharmacologic activation of BAT requires increased blood flow to deliver glucose and oxygen for thermogenesis. However, the glucose consumption far exceeds the vascular response. These findings demonstrate that activated BAT increases glucose uptake beyond what might occur by increased blood flow alone and suggest that activated BAT likely uses glucose for nonthermogenic purposes.

Evaluation of ability of biochemical markers of bone turnover to predict a response to increased doses of HRT

Antiresorptive therapy is usually given in a fixed dose, and we hypothesized that some patients receiving standard doses of hormone replacement therapy (HRT) might benefit from a higher dose, particularly if their bone turnover decreases after increasing the dose of HRT. Eighty-eight women who had been receiving standard-dose (0.625 mg/day) conjugated equine estrogens (CEE) for at least one year were randomized to take either standard-dose (0.625 mg/day, n = 36) or high-dose (1.25 mg/day, n = 52) therapy. Subjects with a uterus were allowed to take either 10 mg of medroxyprogesterone cyclically or 5 mg daily, according to personal preference. Bone Mineral Density (BMD) and biochemical markers of bone turnover were followed for 2 years. Mean bone turnover decreased significantly (-4.1% to -19.1%) after 6 months of high-dose CEE. Decreases in serum BSAP (bone-specific alkaline phosphatase) and serum or urine NTX ( N-terminal telopeptide crosslink of type I collagen) on high-dose therapy were not predictive of an improvement in BMD, but a decrease in serum CrossLaps did predict an improvement in BMD. Mean change in BMD in subjects with a significant decrease in serum CrossLaps at the anteroposterior spine was 3.1% +/- 3.9% versus 1.2% +/- 2.9% for subjects with no significant change in CrossLaps, P < 0.02. There was, however, a wide range of changes in BMD in patients with or without a significant change in CTX on high-dose HRT, making it impossible to predict an improvement in BMD based on an individual's changes in turnover. Measuring of bone density and bone turnover with better precision might be more successful in guiding individual dosing of antiresorptive therapy.

Early changes in serum N-telopeptide and C-telopeptide cross-linked collagen type 1 predict long-term response to alendronate therapy in elderly women

The aim of this study was to determine whether early changes in serum markers of bone resorption could predict long-term responses in bone mineral density (BMD) after alendronate therapy in elderly women. One hundred and twenty women (mean age, 70 yr) were randomized to alendronate or placebo in this double blind, placebo-controlled clinical trial for 2.5 yr. Outcome measures were hip and spine BMD and biochemical markers of bone resorption, including serum N-telopeptide and C-telopeptide cross-linked collagen type I (NTx and CTx, respectively). Serum NTx and CTx were highly correlated at baseline (r = 0.73; P < 0.001) and remained so throughout the study (range, r = 0.36-0.56; all P < 0.05). After treatment with alendronate, serum NTx decreased 30.4+/-16.0% at 6 months, reaching a nadir of -36.7+/-18.0% by 24 months (P < 0.001). Serum CTx decreased 43.5+/-67.0% at 6 months and continued to decrease to 67.3+/-19.3% at 2.5 yr (P < 0.001). Moreover, decreases in serum NTx and CTx at 6 months were correlated with long-term improvements in vertebral BMD at 2.5 yr in patients receiving alendronate therapy (NTx: r = -0.42; CTx: r = -0.31; both P < 0.05). We conclude that early changes in serum NTx and CTx, markers of bone resorption, predict long-term changes in vertebral BMD in elderly women receiving alendronate therapy and provide a useful tool to assess skeletal health.

Serum CTX: a new marker of bone resorption that shows treatment effect more often than other markers because of low coefficient of variability and large changes with bisphosphonate therapy

Serum CrossLaps is a new assay for measuring carboxy-terminal collagen crosslinks (CTX) in serum. This measurement is reported to be more specific to bone resorption than other measurements. However, the utility of this and other markers in monitoring patients on antiresorptive therapy depends on how often changes anticipated with therapy exceed changes attributable to random variability. In a study where subjects received either placebo or pamidronate, we calculated the minimum significant change (MSC), that is, the change that was sufficiently large that it was unlikely to be due to spontaneous variability. We also examined the changes in markers of bone turnover in subjects treated with pamidronate (APD) (30 mg i.v. in 500 ml D5W over 4 hours) to see how often observed changes in turnover after treatment exceeded the MSC. The MSC for serum CTX was 30.2%, and was significantly (P < 0.05) lower than the MSC for urinary NTX (54.0%), and not significantly different from the MSC of urinary DPD (20.6%). Ninety percent of subjects treated with APD had a decline in serum CTX that exceeded the MSC, compared with 74% for bone-specific alkaline phophatase (BSAP), 57% for urinary N-telopeptide cross-links (NTX), and 48% for free deoxypyridinoline. Changes in serum CTX correlated reasonably well with changes in spine BMD after 2 years (r = 0.47), but this correlation did not quite reach statistical significance because of the small number of subjects. In conclusion, the serum CTX assay shows greater utility for assessing efficacy of antiresorptive treatment than some previously described markers.

Moderate alcohol consumption and bone density among postmenopausal women

Chronic alcohol abuse is associated with low bone density and high risk of fracture. However, moderate alcohol consumption may help to maintain bone density in postmenopausal women by increasing endogenous estrogens or by promoting secretion of calcitonin. We conducted a prospective study among a sample of 188 white postmenopausal women (ages 50-74) from the Nurses' Health Study who participated in a health examination between 1993 and 1995 that included bone density assessments of the lumbar spine and proximal femur. Long-term alcohol intake was calculated as the average of the 1980 and 1990 measures from a food frequency questionnaire. Women who consumed 75 g or more of alcohol per week had significantly higher bone densities at the lumbar spine compared with non-drinking women (0.951 vs. 0.849 g/cm2, p = 0.002) after adjusting for age, body mass index (kg/m2), age at menopause, use of postmenopausal estrogens, and smoking status. Further adjustment for physical activity and daily intakes of calcium, vitamin D, protein, and caffeine did not alter the results. We also observed a linear increase in spinal bone density over increasing categories of alcohol intake (p = 0.002), suggesting that alcohol intakes of less than 75 g/week may also be of benefit. This positive association was observed among both current users and never users of postmenopausal estrogens. In contrast to the lumbar spine, femoral bone density was not higher among drinkers compared with nondrinkers, although density did increase among drinkers with increasing level of alcohol consumption. Further research is needed to determine whether moderate alcohol consumption can help to protect against spinal fractures in postmenopausal women. This finding must also be evaluated within a larger scope of the risks and benefits of alcohol on heart disease, breast cancer, and hip fractures.

Utility of biochemical markers of bone turnover in the follow-up of patients treated with bisphosphonates

Biochemical markers of bone turnover are often measured in patients treated with antiresorptive agents to monitor the effects of therapy. In order for a change in these markers to clearly indicate treatment effect, the change in the markers must exceed the amount of spontaneous variation typically seen with no treatment. Based on the measured long-term variability of markers in untreated patients, we defined a minimum significant change (MSC), that is, a change that was sufficiently large that it was unlikely to be due to spontaneous variability. We also examined the changes in markers of bone turnover in subjects treated with pamidronate to see how often observed changes in turnover after treatment exceeded the MSC. We found that urinary markers of bone resorption are best measured on 2-hour fasting samples, because results on random urine showed poor precision and less decline with therapy. We also found that of all the markers, urinary N-telopeptide cross-links (NTX) had the greatest decline after therapy (58%), although it also had the highest long-term variability (29.5%). The marker that most often showed a decline with treatment that exceeded the MSC was serum bone-specific alkaline phosphatase where 74% of observed changes exceeded the MSC. Other markers that often showed a decline with treatment that exceeded the MSC were 2-hour fasting urine NTX and free deoxypyridinoline, where 57% and 48%, respectively, of changes in therapy exceeded the MSC. The ideal marker would combine the large decline after treatment characteristic of NTX (60-70%) with the good precision of bone-specific alkaline phosphatase.

Early changes in biochemical markers of bone turnover predict the long-term response to alendronate therapy in representative elderly women: a randomized clinical trial

Although the antiresorptive agent alendronate has been shown to increase bone mineral density (BMD) at the hip and spine and decrease the incidence of osteoporotic fractures in older women, few data are available regarding early prediction of long-term response to therapy, particularly with regard to increases in hip BMD. Examining short-term changes in biochemical markers incorporates physiologic response with therapeutic compliance and should provide useful prognostic information for patients. The objective of this study was to examine whether early changes in biochemical markers of bone turnover predict long-term changes in hip BMD in elderly women. The study was a double-blind, placebo-controlled, randomized clinical trial which took place in a community-based academic hospital. One hundred and twenty community-dwelling, ambulatory women 65 years of age and older participated in the study. Intervention consisted of alendronate versus placebo for 2.5 years. All patients received appropriate calcium and vitamin D supplementation. The principal outcome measures included BMD of the hip (total hip, femoral neck, trochanter, and intertrochanter), spine (posteroanterior [PA] and lateral), total body, and radius. Biochemical markers of bone resorption included urinary N-telopeptide cross-linked collagen type I and free deoxypyridinoline; markers of bone formation included serum osteocalcin and bone-specific alkaline phosphatase. Long-term alendronate therapy was associated with increased BMD at the total hip (4.0%), femoral neck (3.1%), trochanter (5.5%), intertrochanter (3.8%), PA spine (7.8%), lateral spine (10.6%), total body (2.2%), and one-third distal radius (1.3%) in elderly women (all p < 0.01). In the placebo group, bone density increased 1.9-2.1% at the spine (p < 0.05) and remained stable at all other sites. At 6 months, there were significant decreases in all markers of bone turnover (-10% to -53%, p < 0.01) in women on alendronate. The changes in urinary cross-linked collagen at 6 months correlated with long-term bone density changes at the hip (r = -0.35, p < 0.01), trochanter (r = -0.36, p < 0.01), PA spine (r = -0.41, p < 0.01), and total body (r = -0.34, p < 0.05). At 6 months, patients with the greatest drop in urinary cross-linked collagen (65% or more) demonstrated the greatest gains in total hip, trochanteric, and vertebral bone density (all p < 0.05). A 30% decrease in urinary cross-linked collagen at 6 months predicted a bone density increase of 2.8-4.1% for the hip regions and 5.8-6.9% for the spine views at the 2.5-year time point (p < 0.05). There were no substantive associations between changes in biochemical markers and bone density in the placebo group. Alendronate therapy was associated with significant long-term gains in BMD at all clinically relevant sites, including the hip, in elderly women. Moreover, these improvements were associated with early decreases in biochemical markers of bone turnover. Early dynamic decreases in urinary cross-linked collagen can be used to monitor and predict long-term response to bisphosphonate therapy in elderly women. Future studies are needed to determine if early assessment improves long-term patient compliance or uncovers poor compliance, thereby aiding the physician in maximizing the benefits of therapy.

Randomized trial of pamidronate in patients with thyroid cancer: bone density is not reduced by suppressive doses of thyroxine, but is increased by cyclic intravenous pamidronate

Patients taking suppressive doses of T4 are thought to have accelerated bone loss and increased risk of osteoporosis. We therefore randomize 55 patients taking suppressive doses of T4 to treatment with pamidronate (APD) 30 mg i.v. every 3 months for 2 yr (APD/T4), or placebo (placebo/T4). Patients had measurements of bone mineral density (BMD) of the spine, hip, radius, and total body every 6 months for 2 yr. There was no significant bone loss at any site in the placebo/T4 group. Ninety five percent confidence intervals excluded a rate of bone loss > 0.89%/yr for the spine and > 0.31%/yr at the total hip. When men were excluded from the analysis, there still was no significant bone loss for the placebo/T4 group, and confidence intervals did not change. The APD/T4 group showed increases in spine (4.3%, P = 0.0001), total hip (1.4%, P < 0.05), and trochanteric (3.0%, P = 0.0001) BMDs. In conclusion, premenopausal women and men on suppressive therapy with T4 do not lose bone rapidly, and are not at increased risk of developing osteoporosis. A regimen of 30 mg APD given every 3 months for 2 yr causes significant suppression of bone resorption and increases in BMD, and may be an acceptable alternative treatment for osteoporosis in patients who cannot tolerate oral bisphosphonates.

The effect of PTH antagonist BIM-44002 on serum calcium and PTH levels in hypercalcemic hyperparathyroid patients

BIM-44002, a pure competitive antagonist of parathyroid hormone (PTH), has a high affinity for the PTH/PTHrP receptor in vitro, and can completely inhibit the actions of a PTH agonist in rats in vivo. Toxicology studies in rats and dogs showed BIM-44002 to be devoid of any adverse effects. Therefore we undertook an investigation to evaluate the potential utility of BIM-44002 in lowering elevated serum calcium in three patients with primary hyperparathyroidism. BIM-44002 was administered by continuous intravenous infusion at dosages of 100 microg/hour (370 nmol/hour) for 12 hours, followed by 200 microg/hour for 12 hours, followed by 400 microg/hour for 12 hours. Vital signs and serum ionized and total calcium were monitored hourly and for 3 hours after cessation of the infusion. Blood for PTH determinations was obtained at the same time points. Serum calcium and PTH did not change during and after the infusion of the antagonist. No subject experienced any adverse reactions to the infusion of the antagonist. We conclude that although the PTH antagonist BIM-44002 was effective both in vitro and in vivo in animals, and it was safe in humans, it was not able to lower serum calcium in patients with hyperparathyroidism. Possible reasons for lack of clinical efficacy are discussed.

Short-term hyperthyroidism has no effect on leptin levels in man

Leptin, a 16-kDa adipocyte-derived protein whose circulating levels reflect energy stores, increases the resting metabolic rate and thermogenesis in rodents. Thyroid hormones also increase the basal metabolic rate, but nothing is known about possible interactions between leptin and thyroid hormone. Activation of beta-adrenergic receptors decreases leptin levels in rodents. To test the hypothesis that thyroid hormones, by causing a "functional hyperadrenergic" state, result in decreased leptin concentrations in humans, we studied 22 normal healthy men before and after the administration of T3 for 1 week to induce moderate hyperthyroidism. Short term thyroid hormone excess does not alter circulating leptin concentrations despite a demonstrated effect on heart rate, systolic blood pressure, cholesterol levels, and metabolic indexes of bone turnover. Elucidation of the apparently separate pathways by which thyroid hormones, beta-agonists, and leptin regulate energy expenditure and food intake may have important implications for our understanding of the mechanisms for regulating energy homeostasis in health and disease.

Finasteride therapy does not alter bone turnover in men with benign prostatic hyperplasia--a Clinical Research Center study

Benign prostatic hyperplasia is often treated with finasteride, which inhibits the conversion of testosterone to dihydrotestosterone (DHT). Aside from the prostate, other androgen-dependent tissues seem to be unaffected by selective DHT deficiency, but the effect on bone density in humans has not yet been defined. To study this question, we compared indices of bone turnover and bone mineral density in 35 men treated with finasteride with controls. Bone resorption was assessed by measuring urinary excretion of N-telopeptide cross-links of type I collagen and hydroxyproline, and bone formation was assessed by measuring serum osteoncalcin and bone-specific alkaline phosphatase. Bone density of the spine and hip were assessed by dual energy x-ray absorptiometry. We found that finasteride-treated patients had mean DHT levels 81% lower than controls (P < 0.0001). There were no significant differences between the two groups in any of the markers of bone turnover or measures of bone density. These results suggest that testosterone can maintain bone density in men even in the absence of DHT. Although long term studies are needed, our results suggest that men who take finasteride are not at increased risk for bone loss.

Treatment with growth hormone and IGF-I in growing rats increases bone mineral content but not bone mineral density

Human growth hormone (hGH) and insulin-like growth factor I (IGF-I) both stimulate bone formation and have been proposed as therapeutic agents for osteoporosis. We examined the effect of hGH and IGF-I alone and in combination on bone size, bone mineral content (BMC), and bone mineral density (BMD) in 10- to 12-week old growing female Sprague-Dawley rats. Sixty rats were assigned to treatment with either placebo, hGH, IGF-I, or both for 4 weeks. After 4 weeks, the right femurs and tibias were excised, and ex vivo BMC and the area of the tibia and femur were measured by dual-energy X-ray absorptiometry (DXA); volume of these bones was measured by Archimedes' principle. In addition, proximal tibial bone density was measured directly by peripheral quantitative computerized tomography (pQCT). Bone length, area, and volume in all treated groups was greater than controls. Areal bone density by DXA (BMC/area) was higher in IGF-treated rats and lower in GH-treated rats than in controls. Volumetric bone density (BMC/volume) was lower in treated groups than in controls. Measurements by pQCT confirmed that true bone density was lower in all treated groups than in controls. We conclude that treatment with hGH or IGF-I increased bone size and mineral content but decreased bone density in growing rats. Because areal correction of BMC did not adequately correct for the increased bone volume in IGF-treated rats, results of areal bone density by DXA should be interpreted with caution when treatment causes a disparity in bone size between groups.

Differentiating between orchiectomized rats and controls using measurements of trabecular bone density: a comparison among DXA, histomorphometry, and peripheral quantitative computerized tomography

In studies of rat bone metabolism, trabecular bone density should be measured. Three established methods of measuring trabecular bone include trabecular bone volume by histomorphometry (BV/TV%), trabecular bone density by peripheral quantitative computerized tomography (pQCT), and areal bone density of trabecular-rich regions by dual x-ray absorptiometry (DXA). We compared the ability of these three methods to discriminate between orchiectomized (orchidectomized) rats and controls. Sixteen male Sprague-Dawley rats (400-425 g) were orchiectomized, and 16 others were controls. In vivo spine bone mineral density (BMD) was measured at the beginning of the study and again after 11 weeks. Rats were sacrificed, and ex vivo BMDs of the right femur and tibia were measured by DXA, followed by trabecular bone density of the right proximal tibia by pQCT. BT/TV% of the left proximal tibia was measured by histomorphometry. Differences between groups were detected by all three methods, but both the magnitude of the difference between groups and the variance of the measurements was much greater for histomorphometry and pQCT than for DXA. Consequently, the statistical significance for the difference between groups was comparable for all three methods. Of the sites measured with DXA, the proximal tibia had the greatest statistical significance for the difference between groups. In summary, all three methods can demonstrate the effect of orchiectomy on trabecular bone. The large differences between groups seen by histomorphometry are also seen by pQCT but not by DXA. We conclude that trabecular bone density by pQCT may be a reasonable surrogate for measurements by histomorphometry.

Bone density is normal in male rats treated with finasteride

Bone is an androgen-dependent tissue. It is not known whether normal bony growth and mineralization in males is dependent on testosterone alone, or whether its metabolite, dihydrotestosterone (DHT), also is required. To answer this question, we examined the effect of finasteride, an inhibitor of DHT synthesis, on bone in rats. Three-month-old male rats were treated with placebo, finasteride, or orchidectomy. The bone mineral densities (BMD) of the spine and whole body were measured in vivo by dual x-ray absorptiometry at weeks 0 and 11, and the BMD of the femur and tibia were measured ex vivo at week 11. Histomorphometric analysis was performed on the proximal tibia at week 11. The increase in spine and whole body BMD in finasteride-treated rats did not differ from that in controls, whereas these values were significantly lower in orchidectomized rats. Similarly, the BMD of the femur and tibia and the cancellous bone volume of the proximal tibia in finasteride-treated rats did not differ from those in controls, whereas these values were significantly lower in orchidectomized rats. In summary, bone development and density were normal in rats treated with finasteride. We conclude that selective DHT deficiency is not deleterious to the male rat skeleton.

Indirect estimation of thyroid hormone-binding proteins to calculate free thyroxine index: comparison of nonisotopic methods that use labeled thyroxine ("T-uptake")

There are many alternative ways of estimating free thyroxine (T4) when thyrotropin screening results are abnormal. In addition to free T4 immunoassays, the menu of most automated immunoassay instruments includes a nonisotopic version of the original triiodothyronine (T3)-uptake assay called "T-uptake." We evaluated the ability of five such assays (Access, ES-300, IMx, Magnum Opus, and Stratus) to accurately estimate the free thyroxine index (FTI) in euthyroid, hyperthyroid, and hypothyroid patients with abnormal concentrations of thyroid hormone-binding proteins, and in patients with nonthyroidal illness. For comparison, we calculated a similar FTI, using either T3-uptake or direct measurement of thyroxine-binding globulin (TBG). Euthyroid reference ranges were comparable. Of euthyroid patients with increased TBG, 12-32% and 5-20% had increased or suppressed FTI, respectively, depending on the T-uptake method used. Except for IMx, 6-35% of hypothyroid patients with increased TBG had inappropriately increased FTI. Patients with nonthyroidal illness had comparable results regardless of the method used, and T-uptake methods were variably affected by known inhibitors of thyroid hormone binding. The most reliable T-uptake method appeared to be the IMx, which, despite claims that it measures all thyroid hormone-binding proteins, correlated best with TBG concentrations.

Indirect estimation of thyroid hormone-binding proteins to calculate free thyroxine index: comparison of nonisotopic methods that use labeled thyroxine ("T-uptake")

There are many alternative ways of estimating free thyroxine (T4) when thyrotropin screening results are abnormal. In addition to free T4 immunoassays, the menu of most automated immunoassay instruments includes a nonisotopic version of the original triiodothyronine (T3)-uptake assay called "T-uptake." We evaluated the ability of five such assays (Access, ES-300, IMx, Magnum Opus, and Stratus) to accurately estimate the free thyroxine index (FTI) in euthyroid, hyperthyroid, and hypothyroid patients with abnormal concentrations of thyroid hormone-binding proteins, and in patients with nonthyroidal illness. For comparison, we calculated a similar FTI, using either T3-uptake or direct measurement of thyroxine-binding globulin (TBG). Euthyroid reference ranges were comparable. Of euthyroid patients with increased TBG, 12-32% and 5-20% had increased or suppressed FTI, respectively, depending on the T-uptake method used. Except for IMx, 6-35% of hypothyroid patients with increased TBG had inappropriately increased FTI. Patients with nonthyroidal illness had comparable results regardless of the method used, and T-uptake methods were variably affected by known inhibitors of thyroid hormone binding. The most reliable T-uptake method appeared to be the IMx, which, despite claims that it measures all thyroid hormone-binding proteins, correlated best with TBG concentrations.

Distinguishing hypothyroxinemia due to euthyroid sick syndrome from pituitary insufficiency

Patients with severe nonthyroidal illness may have low serum levels of thyroid hormone and thyroid-stimulating hormone (TSH) indistinguishable from levels in patients with pituitary insufficiency. It is often difficult prospectively to rule out pituitary insufficiency in these patients. Our hypothesis was that patients sufficiently ill to have low free thyroxine index (FT4I) and TSH from nonthyroidal illness (euthyroid sick syndrome, or ESS) would have serum cortisol levels high enough to make pituitary insufficiency unlikely. Serum samples from all patients admitted to the Intensive Care Unit during 2 months were screened for low FT4I, and cortisol levels were measured on those samples. Five of five patients with a diagnosis of ESS had unequivocal elevations of serum cortisol (> 525 nmol/l), arguing against a diagnosis of pituitary insufficiency. Secondary hypothyroidism due to pituitary insufficiency can often be ruled out in patients with severe ESS by documenting appropriate elevated levels of serum cortisol.

Subregion analysis of the rat femur: a sensitive indicator of changes in bone density following treatment with thyroid hormone or bisphosphonates

Measurement of bone mineral density (BMD) by dual X-ray absorptiometry (DXA) is a precise and accurate way to assess changes in BMD due to a variety of causes. However, the degree of bone loss may vary depending on the skeletal site examined. We postulated that interventions that change bone density would have a different effect on an area rich in trabecular bone, such as the distal femur, than on other subregions of the femur. Male Sprague-Dawley rats (325-350 g) were treated with triiodothyronine (T3), a bisphosphonate (pamidronate), or placebo for 21 days and then sacrificed. Ex vivo BMD of the proximal, distal, mid and total femur were measured by DXA. We found that mean BMD of hyperthyroid rats was significantly lower than controls at all femoral subregions. However, the difference in mean BMD between hyperthyroid and control rats was greatest at the distal femur (8.6%). In rats treated with bisphosphonate, mean BMD was significantly higher than controls at the proximal, distal, and total femur. The difference in mean BMD between controls and rats treated with bisphosphonate was greatest at the distal femur (31.8%). Furthermore, pamidronate (APD)-treated rats had lower mean mid-femur BMD than controls. We conclude that changes in BMD after treatment with bisphosphonate or T3 are greatest at the distal femur subregion, and that treatment with bisphosphonate may cause a slight reduction in mid-femur BMD. Future studies examining changes in BMD in the rat femur after interventions that alter mineral metabolism should include subregion analysis.

Normal insulin-like growth factor-I in an elderly woman with acromegaly and medical illness

Insulin-like growth factor-I (IGF-I) has been advocated as a simple and reliable test for confirming the diagnosis of acromegaly and following a patient's response to treatment. We describe an elderly woman admitted to the hospital with altered mental status, congestive heart failure, and arthritis who was noted to have clear features of acromegaly. An IGF-I level was in the normal range, while results of an oral glucose tolerance were diagnostic of acromegaly. As her medical condition, mobility, and nutrition improved, her IGF-I level increased above the normal range and continued to rise when she was seen as an outpatient. Therefore, illness, physical activity, nutritional status, and advanced age must be considered when interpreting IGF-I levels in patients with known or suspected acromegaly.

Chicken soup revisited: calcium content of soup increases with duration of cooking

Because low dietary calcium intake may accelerate bone loss, patients often are advised to increase their dietary intake of calcium. However, some patients may be unable to tolerate good calcium sources such as dairy products. We postulated that the calcium content of soups and stews could be increased by prolonged cooking with a beef bone. Three experiments were done to prove this theory: (1) a bone soup made with a beef bone and distilled water, cooked for 24 hours; (2) a bone-vegetable soup cooked the same way; and (3) a vegetable soup made the same way but without the bone. It was concluded that prolonged cooking of a bone in soup increases the calcium content of the soup when cooked at an acidic, but not at a neutral pH.

Specificity of urinary excretion of cross-linked N-telopeptides of type I collagen as a marker of bone turnover

Urinary excretion of cross-linked N-telopeptide of type I collagen (NTX) has been reported to be a specific indicator of bone resorption. We studied the utility of a new immunoassay for NTX as an indicator of changes in bone resorption caused by treatment with pamidronate (APD) followed by T3. Twenty-two male subjects received either placebo (Group 1) or APD on study days 1-2 (Group 2). One week later all subjects received T3 100 micrograms/day (days 8-15). Urinary NTX, pyridinoline (PYD), hydroxyproline (HYP), and creatinine (cr) were measured on 2-hour fasting urine samples at baseline (day 1), after APD/placebo (day 8), after T3 (day 16), and at days 30 and 58. NTX/cr excretion fell 85% after treatment with APD (P < 0.001 versus baseline), but not after placebo. The fall in mean urinary NTX after receiving APD was greater than the fall in PYD (25%) or HYP (31%) (P < 0.001 NTX versus PYD and HYP). After treatment with APD, NTX excretion remained suppressed below baseline until day 58, whereas PYD and HYP excretion returned to baseline by study day 16. Persistence of APD's effect on bone until day 58 was suggested by the fact that serum calcium and parathyroid hormone levels had not returned to baseline by day 58. On day 16, after all subjects were treated with T3, urinary NTX/cr rose significantly (P < 0.01) in Group 1 (-bisphosphonate) but not in Group 2 (+bisphosphonate).(ABSTRACT TRUNCATED AT 250 WORDS)

Threonine for alanine substitution at position 109 of transthyretin differentially alters human transthyretin's affinity for iodothyronines

The heterozygous substitution of threonine for alanine at amino acid 109 of human transthyretin (TTR) increases its affinity for T4. We compared the affinity of recombinant wild-type (WT) and Thr109-TTRs for various iodothyronines in an attempt to elucidate how this mutation alters the T4-binding site. Homozygous WT and Thr109-TTRs were expressed recombinantly in Escherichia coli, and heterozygous Thr109-TTR was purified from plasma. The affinities of the iodothyronines for TTR were determined by measuring [125I]T4 bound by TTR in the presence of increasing concentrations of unlabeled iodothyronines. Homozygous Thr109-TTR bound T4 with an affinity slightly, but not significantly, greater than that of heterozygous Thr109-TTR. The affinity of Thr109-TTR for all iodothyronines was higher than that of WT TTR. However, the Thr109 mutation increased TTR's affinity for T4, Triac (triiodothyroacetic acid), and T3 to a greater extent than it did for Tetrac (tetraiodothyroacetic acid), EMD21388 (3',5'-dibromo-4',6'-dihydroxy-3-methylflavone), and dextro-T4. These data demonstrate that a subtle change in the structure of the T4-binding channel in TTR differentially alters the affinity of binding of various iodothyronines and suggests that site-directed mutagenesis of residues within the binding channel might clarify the relative importance of specific domains of this binding channel.

Parenteral pamidronate prevents thyroid hormone-induced bone loss in rats

Pamidronate (APD) is a bisphosphonate that prevents bone loss from a variety of causes. We studied the role of APD in preventing thyroid hormone-induced bone loss. A total of 32 rats were assigned to one of four treatment groups: (1) -APD/triiodothyronine (-T3), (2) -APD/+T3, (3) +APD/-T3, or (4) +APD/+T3. In the first of two studies, the rats received APD for the first week and T3 for the second week, and then their blood was analyzed for alkaline phosphatase and osteocalcin. Alkaline phosphatase and osteocalcin were significantly higher (p < 0.05) in hyperthyroid rats (-APD/+T3, 3.9 +/- 0.25 mukat/liter and 23 +/- 1.6 nM, respectively) than in control animals (2.53 +/- 0.28 mukat/liter and 18.3 +/- 1.4 nM, respectively). Hyperthyroid rats pretreated with APD (+APD/+T3) had levels of alkaline phosphatase and osteocalcin no different from controls. In a second study, rats were divided into the same four groups, except they received APD/placebo and T3/placebo concomitantly for 3 weeks. At the end of the study, bone mineral density (BMD) of the femur, spine, and whole body was measured by dual-energy x-ray absorptiometry, and the calcium content of the femora was measured directly. In hyperthyroid rats (-APD/+T3) BMD was significantly lower than in controls in the spine (0.201 +/- 0.004 versus 0.214 +/- 0.002 g/cm2, p < 0.05) and femur (0.204 +/- 0.003 versus 0.218 +/- 0.002, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Therapy with parenteral pamidronate prevents thyroid hormone-induced bone turnover in humans

Bisphosphonates have been shown to decrease bone turnover in a variety of high turnover states. We postulated that pamidronate (APD), a bisphosphonate, could prevent the increased bone turnover caused by thyroid hormone excess. Twenty-two male subjects were randomized to receive either placebo (group 1) or APD (30 mg, iv, daily for 2 days; group 2). Subsequently, all subjects received T3 (50 micrograms, twice daily, for 8 days). Biochemical indices of bone turnover were measured in blood and urine at baseline, after treatment with APD/placebo, and after treatment with T3. The urinary calcium/creatinine ratio (Uca/cr) fell significantly after treatment with APD, but not after treatment with placebo (group 1, 0.131 +/- 0.021; group 2, 0.040 +/- 0.013 mmol Ca/mmol Cr; P < 0.002). After treatment with T3, Uca/cr rose significantly in group 1, but not in group 2 (group 1, 0.275 +/- 0.042; group 2, 0.065 +/- 0.025 mmol Ca/mmol Cr; P < 0.05). Thus, APD prevented the rise in Uca/cr caused by treatment with T3. Similar results were obtained with urinary hydroxyproline and urinary pyridinoline cross-links. We conclude that 8 days of mild thyroid hormone excess in normal men increases bone turnover, and prior administration of APD prevents thyroid hormone-induced increases in bone resorption. APD may be useful in the prevention of thyroid hormone-induced osteopenia.

Thyroxine interactions with transthyretin: a comparison of 10 different naturally occurring human transthyretin variants

Transthyretin (TTR) is a tetrameric protein that transports 15-20% of circulating T4. Alterations in TTR structure can manifest clinically as familial amyloidotic polyneuropathy or euthyroid hyperthyroxinemia. We have measured the relative affinity for T4 of several variant TTR molecules in human plasma. We have compared control plasma to plasma from a patient heterozygous for a [Thr109]TTR mutation associated with a 3-fold increased affinity for T4 and to plasma from patients with familial amyloidotic polyneuropathy with different point mutations in TTR. Relative affinity was measured in an assay in which [125I]T4 bound by TTR was isolated by immunoprecipitation with an antibody specific for TTR. [Thr109]TTR displayed the highest affinity for T4, whereas homozygous [Met30]TTR did not bind appreciable amounts of [125I]T4. The rank order of affinity of the various TTR mutations for T4 was: Thr109 heterozygous > wild type = Ala60 heterozygous = Ile122 heterozygous > His58 heterozygous approximately Tyr77 heterozygous approximately Ser84 heterozygous approximately Ile122 homozygous approximately Met30 heterozygous >> Met30 homozygous TTR. Thus, different point mutations in TTR increase, decrease, or do not affect TTR's affinity for T4. The ability of TTR to form amyloid fibrils does not appear to be related to its affinity for T4. Further study is required to define the molecular basis of alterations in T4 binding induced by point mutations located along the TTR tetramer.

Immunoassay for urinary pyridinoline: the new marker of bone resorption

Urinary pyridinoline (Pyd) and deoxypyridinoline (Dpd) are markers of bone resorption that are elevated above normal in subjects with metabolic bone disease. Total Pyd and Dpd, both free and peptide-bound forms, can be measured by HPLC after hydrolysis and cellulose chromatography. Since free Pyd is the major component of total Pyd in urine, we developed an immunoassay using free Pyd as an immunogen. This assay is much easier to perform than HPLC, requires no sample preparation, and correlates well with total Pyd measurement by HPLC (r = 0.97) and with urinary hydroxyproline (r = 0.90). The antiserum reacts most strongly with free Pyd and Dpd and minimally with glycosylated and large peptide-bound forms. The sensitivity of the Pyd immunoassay is less than 25 nM. The intraassay CV is 5-10%; the interassay CV is 10-15%. Analytic recovery studies indicated negligible sample interference. Furthermore, measurement of the Pyd in the same individuals over a 30 day time period exhibited minimal day-to-day variation. Thus, the Pyd immunoassay provides a rapid and easy method for evaluation of Pyd in urine. Pyd immunoassay may serve as a practical method of screening for metabolic bone disease and for monitoring therapeutic treatment.

Vitamin K and maintenance of skeletal integrity in adults

PURPOSE

To determine the role of vitamin K status in the maintenance of skeletal integrity in adults.

PATIENTS AND METHODS

1. Bone mineral density (BMD) was measured by quantitative digital radiography (QDR) in 50 patients taking a vitamin K antagonist (warfarin) who were recruited from a large urban cardiology practice, and 50 age-, sex- and race-matched controls recruited from the community. 2. The relationship of BMD versus indices of vitamin K status (determined by measuring levels of vitamin K and descarboxyprothrombin in the plasma) in 113 nonanticoagulated adults was assessed.

RESULTS

Measurements of BMD in the hip and spine were similar in anticoagulated subjects and matched controls. Multivariate analysis revealed that use of warfarin was not associated with a lower BMD. Ninety-five percent confidence intervals excluded a 0.06 g/cm2 reduction in BMD associated with the use of warfarin. Indices of vitamin K status did not correlate with BMD in normal subjects.

CONCLUSIONS

Patients receiving long-term maintenance therapy with a vitamin K antagonist have normal bone density. BMD is unrelated to vitamin K status in nonanticoagulated subjects. These data suggest that vitamin K does not have a major role in maintenance of skeletal integrity in adults.

Production and functional analysis of normal and variant recombinant human transthyretin proteins

The most common form of hereditary systemic amyloidosis is familial amyloidotic polyneuropathy associated with single amino acid changes in the plasma protein, transthyretin. In addition, there are two variants of transthyretin (Ser6 and Thr109) not associated with familial amyloidotic polyneuropathy but with familial euthyroid hyperthyroxinemia, also an autosomal dominant disorder. In these autosomal dominant diseases, most affected individuals are heterozygous and therefore have hybrid forms of the tetrameric plasma transthyretin. In order to study the structure/function relationships of homozygous variant transthyretins, normal human transthyretin and five variant transthyretins (Gly6----Ser, Leu58----His, Thr60----Ala, Ile84----Ser, and Ala109----Thr) were produced in Escherichia coli using the expression vector, pCZ11, and site-directed mutagenesis. These recombinant transthyretin (r-TTR) proteins showed the correct size (14 kilodaltons) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western analysis and self-associated into tetramers as determined by size exclusion chromatography. Recombinant normal, Ser6, and Ala60 r-TTRs had an affinity for thyroxine indistinguishable from normal human TTR purified from plasma, whereas His58 and Ser84 r-TTRs had significantly reduced affinity. On the other hand, Thr109 r-TTR had a much higher affinity, probably due to its position within the thyroxine-binding pocket. Expression of mutant transthyretins in E. coli provides the opportunity to study structure/function relationships and amyloid-forming capabilities induced by single amino acid substitutions in the transthyretin molecule.

Subtle glucocorticoid excess in patients with adrenal incidentaloma

Incidentally discovered adrenal tumors (incidentalomas) are fairly common since the advent of noninvasive methods of imaging the abdomen. Patients with incidentaloma usually undergo screening for overproduction of glucocorticoids by measurement of basal steroid excretion. We describe an asymptomatic patient with an incidentaloma with normal basal steroid excretion whose only manifestation of subtle steroid overproduction was the failure of steroid excretion to be suppressed normally with dexamethasone. It appears tht the more careful the search for subtle evidence of steroid overproduction in patients with incidentaloma, the more common the finding; perhaps up to 50% of patients with incidentaloma have some subtle steroid overproduction. We review the literature on this subject, and evaluate the various possible approaches of how intensively to study steroid dynamics in patients with incidentaloma.

A point mutation in transthyretin increases affinity for thyroxine and produces euthyroid hyperthyroxinemia

In a family expressing euthyroid hyperthyroxinemia, an increased association of plasma thyroxine (T4) with transthyretin (TTR) is transmitted by autosomal dominant inheritance and is secondary to a mutant TTR molecule with increased affinity for T4. Eight individuals spanning three generations exhibited the abnormality. Although five of eight individuals had elevated total T4 concentrations, all affected individuals were clinically euthyroid and all had normal free T4 levels. Purified TTR from the propositus had an affinity for 125I-T4 three times that of control TTR. Exons 2, 3, and 4 (representing greater than 97% of the coding sequence) of the TTR gene of DNA prepared from the propositus' peripheral blood leukocytes were amplified using the polymerase chain reaction (PCR) and were sequenced after subcloning. Exons 2 and 3 were indistinguishable from normal. In 50% of clones amplified from exon 4, a substitution of adenine (ACC) for guanine (GCC) in codon 109 resulted in the replacement of threonine-for-alanine, a mutation confirmed by amino acid sequencing of tryptic peptides derived from purified plasma TTR. The adenine-for-guanine substitution abolishes one of two Fnu 4H I restriction sites in exon 4. PCR amplification of exon 4 of TTR and restriction digestion with Fnu 4H I confirmed that five affected family members with increased binding of 125I-T4 to TTR are heterozygous for the threonine 109 substitution that increases the affinity of this abnormal TTR for T4.