Imaging of metabolic bone diseases

Spectrum of microarchitectural bone disease in inborn errors of metabolism: a cross-sectional, observational study

BACKGROUND

Patients diagnosed with inborn errors of metabolism (IBEM) often present with compromised bone health leading to low bone density, bone pain, fractures, and short stature. Dual-energy X-ray absorptiometry (DXA) is the current gold standard for clinical assessment of bone in the general population and has been adopted for monitoring bone density in IBEM patients. However, IBEM patients are at greater risk for scoliosis, short stature and often have orthopedic hardware at standard DXA scan sites, limiting its use in these patients. Furthermore, DXA is limited to measuring areal bone mineral density (BMD), and does not provide information on microarchitecture.

METHODS

In this study, microarchitecture was investigated in IBEM patients (n = 101) using a new three-dimensional imaging technology high-resolution peripheral quantitative computed tomography (HR-pQCT) which scans at the distal radius and distal tibia. Volumetric BMD and bone microarchitecture were computed and compared amongst the different IBEMs. For IBEM patients over 16 years-old (n = 67), HR-pQCT reference data was available and Z-scores were calculated.

RESULTS

Cortical bone density was significantly lower in IBEMs associated with decreased bone mass when compared to lysosomal storage disorders (LSD) with no primary skeletal pathology at both the radius and tibia. Cortical thickness was also significantly lower in these disorders when compared to LSD with no primary skeletal pathology at the radius. Cortical porosity was significantly greater in hypophosphatasia when compared to all other IBEM subtypes.

CONCLUSION

We demonstrated compromised bone microarchitecture in IBEMs where there is primary involvement of the skeleton, as well as IBEMs where skeletal complications are a secondary outcome. In conclusion, our findings suggest HR-pQCT may serve as a valuable tool to monitor skeletal disease in the IBEM population, and provides insight to the greatly varying bone phenotype for this cohort that can be used for clinical monitoring and the assessment of response to therapeutic interventions.

Low bone mineral density due to secondary hyperparathyroidism in the GlatmTg(CAG-A4GALT) mouse model of Fabry disease

Low bone mineral density (BMD)—diagnosed as osteoporosis or osteopenia—has been reported as a new characteristic feature of Fabry disease; however, the mechanism underlying the development of low BMD is unknown. We previously revealed that a mouse model of Fabry disease [Gla^tmTg(CAG‐A4GALT)] exhibits impaired functioning of medullary thick ascending limb (mTAL), leading to insufficient Ca²⁺ reabsorption and hypercalciuria. Here, we investigated bone metabolism in Gla^tmTg(CAG‐A4GALT) mice without marked glomerular or proximal tubular damage. Low BMD was detected by 20 weeks of age via micro‐X‐ray‐computed tomography. Bone histomorphometry revealed that low BMD results by accelerated bone resorption and osteomalacia. Plasma parathyroid hormone levels increased in response to low blood Ca²⁺—not plasma fibroblast growth factor 23 (FGF‐23) elevation—by 5 weeks of age and showed progressively increased phosphaturic action. Secondary hyperparathyroidism developed by 20 weeks of age and caused hyperphosphatemia, which increased plasma FGF‐23 levels with phosphaturic action. The expression of 1α‐hydroxylase [synthesis of 1α,25(OH)₂D₃] in the kidney did not decrease, but that of 24‐hydroxylase [degradation of 1α,25(OH)₂D₃] decreased. Vitamin D deficiency was ruled out as the cause of osteomalacia, as plasma 1α,25(OH)₂D₃ and 25(OH)D₃ levels were maintained. Results demonstrate that secondary hyperparathyroidism due to mTAL impairment causes accelerated bone resorption and osteomalacia due to hyperphosphaturia and hypercalciuria, leading to low BMD in Fabry model mice.

Factors associated with diffusely increased renal uptake of Tc-99m diphosphono-propanedicarboxylic acid on bone scintigraphy in patients with end-stage renal disease

OBJECTIVE

We aimed to determine the factors contributing toward diffusely increased renal uptake on bone scintigraphy using technetium-99m (Tc-99m) diphosphono-propanedicarboxylic acid (DPD) in patients with end-stage renal disease.

PATIENTS AND METHODS

One-hundred and forty-three bone scintigraphies, performed between June 2007 and July 2013, in 135 patients with chronic kidney disease were analyzed retrospectively, including 22 bone scintigraphies (15 patients; eight women; seven men) with glomerular filtration rates less than 15 ml/min/1.73 m. Patients with nephrocalcinosis were excluded. The clinical records of medication and underlying disease were reviewed retrospectively. The presence of renal artery calcification was visually estimated and the Hounsfield unit (HU) of renal parenchyma was measured by abdominal and pelvic nonenhanced computed tomography.

RESULTS

Two patients underwent peritoneal dialysis and 13 underwent hemodynamic dialysis. Diffusely increased renal Tc-99m DPD uptake was observed on 15 of 22 (68%) bone scintigraphy images. Laboratory test results were not significantly different between the patients with or without increased renal uptake. A history of inflammatory conditions or antibiotic administration did not correlate with kidney visualization. The significant factor for diffuse renal tracer uptake on multivariate analysis was renal artery calcification (odds ratio: 18.42; 95% confidence interval: 2.01-79.43; P<0.001). The mean HU values were significantly higher in patients with diffuse renal tracer uptake (P=0.04) and renal artery calcification (P=0.02).

CONCLUSION

Small renal arteriolar calcification and a higher HU value of renal parenchyma could be associated with diffusely increased renal Tc-99m DPD uptake in patients with end-stage renal disease.

Utility of Plain Radiographs in Metabolic Bone Disease - A Case-Based Pictorial Review from a Tertiary Centre

In this era of advanced high-tech imaging, the utility of plain radiographs in conditions of the bone is increasingly being overseen by both clinicians and radiologists. Plain radiography is the first-line, essential screening or diagnostic tool for diverse bone diseases, where magnetic resonance imaging (MRI) may be non-contributory. Plain radiographs often play a pivotal role in diagnosing metabolic bone disorders. This paper from a single tertiary care centre discusses ten real-life patients with metabolic bone conditions and other bone diseases with near-normal MRI of the spine, in whom plain radiographs revealed subtle findings and aided in making diagnoses.

Each of these cases had a non-specific clinical presentation. They all showed inconclusive features on MRI, but subtle important radiographic findings led to a specific diagnosis.

Plain radiography is key in diagnosing bone diseases. Many of these metabolic conditions clinically mimic rheumatologic conditions owing to non-specific arthralgia and back pain. Familiarity with subtle radiographic findings of these conditions may lead to early diagnosis and treatment, resulting in improved patient outcomes.

"Dark" carbon dots specifically "light-up" calcified zebrafish bones

Because accidents, disease and aging compromise the structural and physiological functions of bones, the development of an in vivo bone imaging test is critical to identify, detect and diagnose bone related development and dysfunctions. Recent advances in fluorescence instrumentation offer a new alternative for traditional bone imaging methods. However, the development of new in vivo bone imaging fluorescence materials has significantly lagged behind. Here we show that carbon dot nanoparticles (C-dots) with low quantum yield ("dark") bind to calcified bone structures of live zebrafish larvae with high affinity and selectivity. Binding resulted in a strong enhancement of luminescence that was not observed in other tissues, including non-calcified endochondral elements. Retention of C-dots by bones was very stable, long lasting, and with no detectable toxicity. Furthermore, we found C-dots to be a suitable carrier to deliver fluorescein to bones. These observations support a novel and revolutionary use of C-dots as highly specific bioagents for bone imaging and diagnosis, and as bone-specific drug delivery vehicles.

Imaging Findings and Evaluation of Metabolic Bone Disease

Bone is a dynamic organ of the endoskeleton, playing an important role in structural integrity, mineral reservoirs, blood production, coagulation, and immunity. Metabolic bone disease encompasses a broad spectrum of inherited and acquired disorders that disrupt the normal homeostasis of bone formation and resorption. For patients affected by these processes, radiologic imaging plays a central role in diagnosis, monitoring treatment, and risk stratification. Radiologists should be familiar with the diseases, intimately aware of the imaging findings, and possessive of multimodality expertise to wisely guide the best practice of medicine. The purpose of this paper is to review the imaging features and characteristics of the most common types of metabolic bone disease with highlights of clinically relevant information so that readers can better generate appropriate differential diagnoses and recommendations. For this review, a thorough literature search for the most up-to-date information was performed on several key types of metabolic bone disease: osteoporosis, osteomalacia, rickets, scurvy, renal osteodystrophy, hyperparathyroidism, Paget’s disease, osteogenesis imperfecta, acromegaly, and osteopetrosis. Although they all affect the bone, these diseases have both shared characteristic features that can be discerned through imaging.

Osteoporosis and osteomalacia - clinical and diagnostic problems

Aim: to define main clinical and diagnostical problems related to osteoporosis and osteomalacia. Literature data showed that not only osteoporosis but osteomalacia may be the reason for decreasing of mechanical properties of skeleton with risk of low-energy fractures. The solution of associated medical and social problems is difficult because DEXA does not allow to differentiate between osteoporosis and osteomalacia that leads to misdiagnosis and unnecessary prescription of antiosteoporotic drugs. This approach is pathogenetically unproved and even may be harmful for the patient. Osteoporosis and osteomalacia does not exclude each other so bone mass reducing in one cohort of patient may be due to osteoporosis, other - osteomalacia and some of them - combinations of both. Another point is that results of controlled clinical trials that evaluated efficacy of antiosteoporotic drugs without differentiative histology tests for osteoporosis and osteomalacia are of doubtful value. As the bone biopsy that is necessary for osteomalacia diagnosis is invasive procedure there is need in definition of clear criteria when it has to be done in patient with reduced bone mass.

Microstructural, densitometric and metabolic variations in bones from rats with normal or altered skeletal states

Background

High resolution μCT, and combined μPET/CT have emerged as non-invasive techniques to enhance or even replace dual energy X-ray absorptiometry (DXA) as the current preferred approach for fragility fracture risk assessment. The aim of this study was to assess the ability of µPET/CT imaging to differentiate changes in rat bone tissue density and microstructure induced by metabolic bone diseases more accurately than current available methods.

Methods

Thirty three rats were divided into three groups of control, ovariectomy and vitamin-D deficiency. At the conclusion of the study, animals were subjected to glucose (¹⁸FDG) and sodium fluoride (Na¹⁸F) PET/CT scanning. Then, specimens were subjected to µCT imaging and tensile mechanical testing.

Results

Compared to control, those allocated to ovariectomy and vitamin D deficiency groups showed 4% and 22% (significant) increase in ¹⁸FDG uptake values, respectively. DXA-based bone mineral density was higher in the vitamin D deficiency group when compared to the other groups (cortical bone), yet μCT-based apparent and mineral density results were not different between groups. DXA-based bone mineral density was lower in the ovariectomy group when compared to the other groups (cancellous bone); yet μCT-based mineral density results were not different between groups, and the μCT-based apparent density results were lower in the ovariectomy group compared to the other groups.

Conclusion

PET and micro-CT provide an accurate three-dimensional measurement of the changes in bone tissue mineral density, as well as microstructure for cortical and cancellous bone and metabolic activity. As osteomalacia is characterized by impaired bone mineralization, the use of densitometric analyses may lead to misinterpretation of the condition as osteoporosis. In contrast, µCT alone and in combination with the PET component certainly provides an accurate three-dimensional measurement of the changes in both bone tissue mineral density, as well as microstructure for cortical and cancellous bone and metabolic activity.

Is there any association between leptin levels and bone mineral density in haemophiliac men?

INTRODUCTION

Conflicting data exist regarding the role of leptin in bone metabolism. The purpose of the present study was to investigate serum leptin concentrations in male patients with haemophilia A and B, a disease known to be associated with low bone mass.

MATERIAL AND METHODS

Eighty-one male patients, aged 45.4 ±15 years, were screened. Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry (DXA) in lumbar spine (LS), femoral neck (FN) and total hip (TH).

RESULTS

Low bone mass was diagnosed in 20 patients (24.7%). Serum leptin concentrations were strongly associated with body weight (r s = 0.457, p = 0.0001) and body mass index (BMI) (r s = 0.491, p = 0.0001). In unadjusted analysis leptin was inversely associated with BMD in LS (r s = -0.255, p = 0.023), but not in FN and TH (r s = -0.205, p = 0.068 and r s = -0.191, p = 0.090, respectively). However, after adjusting for BMI and body weight, leptin was inversely associated with BMD in FN (F 1,76 = 7.727, p = 0.007, β = -0.371, ΔR (2) = 0.089) and TH (F 1,76 = 4.533, p = 0.036, β = -0.290, ΔR (2) = 0.054), but not in LS (F 1,75 = 2.076, p = 0.154, β = -0.202, ΔR (2) = 0.026). No association was found between age, presence of HBV, HCV or HIV infection or alkaline phosphatase and leptin levels.

CONCLUSIONS

Our study showed a negative association between circulating leptin levels and bone mass in males, independently of body weight and BMI.

Monostotic Paget's disease involving the calcaneus encountered incidentally on bone scintigraphy

Isolated involvement of calcaneus with Paget's disease of bone is highly unusual, with very few cases reported in the world literature. We present herein a unique 69-year-old male patient with monostotic Paget's disease of the left calcaneus discovered incidentally during a whole body bone scintigraphy. Since most bone scans are performed for evaluating osseous metastases, differentiating Paget's disease from overlapping metastases may be of significant clinical value. We discuss further the importance of whole body bone scan and other imaging modalities in establishing the correct diagnoses in such cases.

Block-copolymer-assisted synthesis of hydroxyapatite nanoparticles with high surface area and uniform size

We report the synthesis of hydroxyapatite nanoparticles (HANPs) by the coprecipitation method using calcium D-gluconate and potassium hydrogen phosphate as the sources of calcium and phosphate ions, respectively, and the triblock copolymer F127 as a stabilizer. The HANPs were characterized using scanning electron microscopy, x-ray diffraction, and nitrogen adsorption/desorption isotherms. Removal of F127 by solvent extraction or calcination alters the structure of HANPs. The solvent-extracted HANPs were single crystals with their 〈001〉 axis oriented along the rod axis of the HANP, whereas the calcined HANPs contained two crystal phases that resulted in a spherical morphology. The calcined HANPs had much higher surface area (127 m² g^-1) than the solvent-extracted HANPs (44 m² g^-1).

Room temperature synthesis of highly hemocompatible hydroxyapatite, study of their physical properties and spectroscopic correlation of particle size

Needle shaped nanoparticles of hydroxyapatite (HA) have been synthesized at room temperature using orthophosphoric acid as the source of (PO4)3- ions, while calcium chloride, the calcium source, is suitably complexed with citric acid/tartaric acid/acetic acid. The presence of ligands inhibits the growth along [001] and [100] directions of the crystal and thus, helps in formation of needle shaped nanoparticles. The chemical compositions of the samples have been established through AAS and FTIR spectroscopy, while the crystallinity has been assessed through XRD and by the spectral changes in the υ1 and υ3 frequencies of the phosphate group in the respective FTIR spectra. The particle sizes of the samples have been determined from line broadening studies and correlations have been established between the curve fitted percentage area of FTIR and full width half height (FWHH) of the XRD peaks. TEM studies revealed the particle to be needle-shaped with a length and diameter in the range of 20-65 nm and 4-11 nm respectively. Changes in the surface charge of the water dispersed HA samples have been determined at different pH and the isoelectric point for the samples have been found in the range of 3.1-3.4. Finally, the morphology, surface area and hemocompatibility characteristics of the HA samples, prepared by using different complexing agents, have been compared.

[Radiological diagnosis of osteoporosis]

Having at their disposal a wide range of imaging techniques, radiologists play a crucial role in the diagnostic evaluation of patients with osteoporosis. The radiological tests range from dual energy X-ray absorptiometry (DXA), which is the only reference method accepted by the WHO, to conventional radiographs for fracture characterization, to more recent techniques for analyzing trabecular structure, and the findings are decisive in initiating correct management of osteoporosis patients. This review provides an overview of established radiological techniques and an outline of new diagnostic approaches.

Dual-energy X-ray absorptiometry and quantitative ultrasound in patients with Paget's disease of bone before and after treatment with zoledronic acid: association with serum bone markers and Dickkopf-1

The main aim of this study was to determine the effect of zoledronic acid (ZOL) on parameters of dual-energy X-ray absorptiometry (DXA) and quantitative ultrasound (QUS) in unaffected bones of patients with Paget's disease of bone (PDB). The secondary aim was the association of bone markers and Dickkopf (DKK)-1 with parameters of DXA and QUS. Ten consecutive patients with polyostotic PDB (median age: 63 yr) received a single 5-mg ZOL infusion. The patients were subjected to calcaneal QUS and DXA of both lumbar spine (LS) and femoral neck (FN). Blood samples for serum bone markers and DKK-1 were serially obtained for 12 mo. There was a significant increase in LS (p=0.005) and FN bone mineral density (BMD) (p=0.021) 12 mo after ZOL infusion. QUS parameters remained unaffected throughout the study. A significant correlation between broadband ultrasound attenuation and DKK-1 (p<0.001) and between speed of sound and DKK-1 (p=0.033) at baseline was found, which remained significant after adjustment for gender, age, and body mass index. Our data suggest that a single ZOL infusion significantly increases nonpagetic BMD 12 mo after treatment but has no effect on QUS parameters or DKK-1. Significant correlations were observed between QUS parameters and DKK-1 at baseline.