Central hypothyroidism

Pituitary dysfunction due to sports injuries

Traumatic brain injury (TBI) during sports activities may lead to dysfunction of the pituitary gland. Even mild TBIs have been shown to have the potential to induce pituitary dysfunction. The clinical picture of pituitary dysfunction subsequent to TBIs may mimic the post-TBI period itself. Pituitary hormone deficiencies may improve or new ones may be observed over time. For this reason, hypopituitarism should be considered both during the acute phase and in the recovery period. The most prevalent pituitary hormone deficiency that follows a sports injury is growth hormone (GH) deficiency. Despite the established knowledge regarding the deleterious consequences of GH deficiency in the athletes, the efficacy of replacement therapy remains controversial. Concurrently, given the potential for GH to be utilised for doping purposes, a consensus on the monitoring of these patients remains elusive. There is a necessity for further systematic and large-scale studies on the epidemiology, pathophysiological mechanisms, screening algorithms, and prevention strategies related to sports-related pituitary dysfunction.

Hypothyroidism

Hypothyroidism, the deficiency of thyroid hormone, is a common condition worldwide. It affects almost all body systems and has a wide variety of clinical presentations from being asymptomatic to, in rare cases, life threatening. The classic symptoms of hypothyroidism include fatigue, lethargy, weight gain, and cold intolerance; however, these symptoms are non-specific and the diagnosis is typically made on biochemical grounds through serum thyroid function tests. The most common cause of hypothyroidism is chronic autoimmune thyroiditis (Hashimoto's thyroiditis), although other causes, including drugs (such as amiodarone, lithium, and immune checkpoint inhibitors), radioactive-iodine treatment, and thyroid surgery, are frequent. Historically, severe iodine deficiency was the most common cause. Reference ranges for thyroid function tests are based on fixed percentiles of the population distribution, but there is increasing awareness of the need for more individualised reference intervals based on key factors such as age, sex, and special circumstances such as pregnancy. Levothyroxine monotherapy is the standard treatment for hypothyroidism; it is safe and inexpensive, restores thyroid function tests to within the reference range, and improves symptoms in the majority of patients. However, 10% of patients have persistent symptoms of ill health despite normalisation of thyroid function tests biochemically and a substantial proportion of patients on levothyroxine have thyroid-stimulating hormone concentrations outside the reference range. Ongoing symptoms despite levothyroxine treatment has led to some patients using liothyronine or desiccated thyroid extract. Taken together, these factors have led to intense debate around the treatment thresholds and treatment strategies for hypothyroidism. In this Seminar, we review the epidemiology, genetic determinants, causes, and presentation of hypothyroidism; highlight key considerations and controversies in its diagnosis and management; and provide future directions for research.

Endocrine disorders associated with obesity

Several endocrine disorders, including diabetes, insulinoma, Cushing syndrome, hypothyroidism, polycystic ovarian syndrome, and growth hormone deficiency, are associated with obesity. The mechanisms underlying the development of obesity vary according to the abnormalities of endocrine function. The primary actions of insulin, glucocorticoids (GCs), thyroid hormone, and growth hormone are associated with energy metabolism in the liver, muscle, adipose tissue, and other tissues. This chapter describes the pathogenesis of obesity and metabolic dysfunction associated with excess insulin or GCs and the deficiency of thyroid hormone or growth hormone.

Association of Low-Normal Free T4 Levels With Future Major Depression Development

Context

Hyperthyroidism and overt and subclinical hypothyroidism are associated with major depression; however, the association of major depression across the spectrum of thyroid function within the normal range is unknown.

Objective

We investigated whether higher or lower levels of free thyroxine (T4) and thyrotropin (TSH) within the normal range are associated with major depression.

Methods

This was a retrospective cohort study of 66 960 participants with normal thyroid function who visited for health checkups (St. Luke's International Hospital, 2005-2018). The primary outcome was the development of major depression during the follow-up period. Participants were divided into 3 equal groups based on baseline free T4 or TSH values (low-, middle-, or high-normal), and the incidence of major depression was compared using the Cox proportional hazard model after adjusting for potential covariates.

Results

During the median follow-up of 1883 days, 1363 (2.0%) patients developed major depression. The low-normal free T4 group had a significantly higher risk of major depression (adjusted HR 1.15; 95% CI, 1.01-1.31), but not the high-normal free T4 group or TSH groups. The association between low-normal free T4 and the development of major depression was maintained, rather more obvious, upon exclusion of participants whose thyroid hormone levels became abnormal during follow-up compared with data from all participants (adjusted HR 1.24; 95% CI, 1.07-1.43).

Conclusion

In this cohort, low-normal free T4 was associated with an increased risk of future major depression, even if subsequent hormone levels were maintained within the normal range. The magnitude of the impact of low-normal free T4 was relatively mild.

Diagnosis and Treatment of Nonfunctioning Pituitary Adenomas with Thyroid Disorders

OBJECTIVE

Patients with nonfunctioning pituitary adenoma (NFPA) can present with different types of thyroid disorders, which are easily misdiagnosed or missed and can even result in serious clinical consequences. This study was to summarize the different types of thyroid disorders in patients with NFPA with the aim of providing references for the diagnosis and treatment of such patients.

MATERIALS AND METHODS

The data of pituitary adenoma (PA) patients who underwent surgical treatment at Xuanwu Hospital, Capital Medical University, from 2017 to 2021 were retrospectively analyzed, and NFPA patients with preoperative thyroid disorders were screened out to analyze their imaging, endocrine, treatment, and prognosis data. Also, thyroid disorders were classified to summarize diagnostic methods and treatment principles for different types of thyroid disorders.

RESULTS

A total of 399 NFPA patients were included in this study, of which 67 (16.8%) had thyroid disorders before surgery. Fifty-four patients had (13.5%) central hypothyroidism (CH) caused by NFPA and were treated with levothyroxine (L-T4) supplementation before and after operation. Eleven patients (2.8%) had primary hypothyroidism and were treated with L-T4 during the perioperative period, and long-term treatment of primary hypothyroidism was provided after surgery. Two NFPA patients (0.5%) were combined with primary hyperthyroidism and treated with medication for primary hyperthyroidism after tumor resection.

CONCLUSION

Thyroid disorders are relatively common in patients with NFPA, but are difficult to be diagnosed due to their different types. CH is the most common type of thyroid disorder, which requires aggressive L-T4 supplementation during the preoperative period. The primary disease of the thyroid gland is easily missed when NFPA is combined with primary hypothyroidism or primary hyperthyroidism, and the thyroid function test results require to be analyzed carefully for continued treatment for thyroid disease after resection of the NFPA.

Bexarotene-induced central hypothyroidism assessed by TRH stimulation test in cutaneous T-cell lymphoma patients

Bexarotene-induced central hypothyroidism (CH), for which levothyroxine (LT4) replacement is recommended, has been shown to be caused by pituitary but not hypothalamic disorder experimentally, though the underlying mechanism in humans remains unclear. Here, the pathophysiology of bexarotene-induced CH was examined using a TRH stimulation test in cutaneous T-cell lymphoma (CTCL) patients. In this retrospective longitudinal observational study, serum TSH and free T4 (F-T4) levels were measured in 10 euthyroid patients with CTCL during 24 weeks of bexarotene treatment. TRH stimulation testing was performed following CH diagnosis, with LT4 replacement dosage adjusted to maintain F-T4 at the pre-treatment level. After one week of bexarotene administration, all 10 patients developed CH, based on combined findings of low or low-normal F-T4 with low or normal TSH levels. TSH peak response after a stimulation test at one week was reached at 30 minutes. However, that was <4 μIU/mL in all patients, indicating a blunted though not exaggerated and delayed TSH response. In eight who continued bexarotene for 24 weeks, median LT4 replacement dosage was 125 (range, 75-150) μg/day. TSH level at 30 as well as 15, 60, 90, and 120 minutes after TRH stimulation was significantly correlated with LT4 replacement dosage (ρ = -0.913, p = 0.002), whereas TSH and F-T4 basal levels at one week were not. These results suggest that pituitary hypothyroidism is responsible for bexarotene-induced CH, while TSH levels after TRH stimulation precisely reflect residual pituitary-thyroid function in patients receiving bexarotene.

Immunotherapy-Associated Hypothyroidism: Comparison of the Pre-Existing With De-Novo Hypothyroidism

BACKGROUND

Immunotherapy has revolutionized the treatment of solid malignancies, but is associated with endocrine-related adverse events. This study aims to dissect the natural course of immunotherapy-induced hypothyroidism and provide guidance regarding diagnosis and management in patients with and without pre-existing hypothyroidism.

METHODS

A retrospective analysis was conducted using patients who received immunotherapy between 2010-2019 within a multicenter hospital system. Participants were separated in three groups-those with pre-existing hypothyroidism, those who developed primary hypothyroidism and those with hypophysitis within a year of their first immunotherapy. Serial effects of immunotherapy on thyroid function tests (TFTs) and levothyroxine dosing were evaluated.

RESULTS

822 patients were screened, with 85 determined to have pre-existing hypothyroidism, 48 de-novo primary hypothyroidism and 12 de-novo hypophysitis. All groups displayed fluctuations in TFTs around weeks 6-8 of treatment. In the pre-existing hypothyroidism group, the levothyroxine dose was higher at 54 weeks than at baseline with the difference showing a trend towards statistical significance (p=0.06). The observed mean levothyroxine dose was significantly lower than the mean calculated weight-based dose for all groups. This finding was most clinically significant for the de-novo hypophysitis group (mean difference: -58.3 mcg, p<0.0001). The mean 0.9 mcg/kg levothyroxine dose at week 54 for the de-novo hypophysitis group was statistically lower than the other groups (p=0.009).

CONCLUSION

It is reasonable to screen with TFTs every 4 weeks, and space out TFTs surveillance to every 12 weeks after week 20. Our findings suggest a more conservative approach for levothyroxine dosing in those developing de-novo hypothyroidism, especially hypophysitis, such as initiating at 0.9-1.2 mcg/kg.

Oxcarbazepine was associated with risks of newly developed hypothyroxinaemia and impaired central set point of thyroid homeostasis in schizophrenia patients

AIMS

Hypothyroxinaemia might be easily ignored, because attention is typically paid to individuals with elevated thyroid stimulating hormone (TSH). In this study, we aimed to evaluate the association of oxcarbazepine use as adjuvant for treatment of schizophrenia with hypothyroxinaemia and central set point of thyroid homeostasis.

METHODS

This retrospective cohort study was conducted in the Second Affiliated Hospital of Xinxiang Medical University. Inpatients with a diagnosis of schizophrenia admitted between January 2016 and October 2019 with normal thyroid function at admission were included. Oxcarbazepine use was the exposure measure. Newly developed hypothyroxinaemia was the primary outcome measure and parameters of thyroid homeostasis central set point as measured by TSH index and thyroid feedback quantile-based index (TFQI) were the secondary outcome measures.

RESULTS

In total, 1207 eligible patients were included. The occurrence of hypothyroxinaemia in patients who received oxcarbazepine was higher (35/107, 32.7%) than in those patients who did not (152/1099, 13.8%), with adjusted relative risk of 2.24 and 95% confidence interval of 1.57 and 3.17. Oxcarbazepine use was associated with greater reduction in TSH index (adjusted β -0.33 and 95% confidence interval -0.48, -0.19) and TFQI (adjusted β -0.24 and 95% confidence interval -0.31, -0.16).

CONCLUSION

Oxcarbazepine use was independently associated with increased risk of developing hypothyroxinaemia, and greater reduction in TSH index and TFQI, suggesting that impaired central set point of thyroid homeostasis might be involved in the mechanism of oxcarbazepine-induced hypothyroxinaemia.

Thyroid Function in Adults with Prader-Willi Syndrome; a Cohort Study and Literature Review

Prader–Willi syndrome (PWS) is a complex genetic syndrome combining hypotonia, hyperphagia, a PWS-specific neurocognitive phenotype, and pituitary hormone deficiencies, including hypothyroidism. The low muscle mass associated with PWS causes a low energy expenditure due to a low basal metabolic rate. Combined with increased energy intake due to hyperphagia, this results in a high risk of obesity and associated cardiovascular disease. To reduce the high mortality in PWS (3% yearly), exercise is extremely important. As hypothyroidism can impair exercise tolerance, early detection is crucial. We performed a literature search for articles on hypothyroidism in PWS, measured thyroid hormone (TH) levels in 122 adults with PWS, and performed a medical file search for medication use. Hypothyroidism (low free thyroxin) was present in 17%, and often central in origin (80%). Triiodothyronine levels were lower in patients who used psychotropic drugs, while other TH levels were similar. One in six patients in our cohort of adults with PWS had hypothyroidism, which is more than in non-PWS adults (3%). We recommend yearly screening of free thyroxin and thyroid-stimulating hormone levels to avoid the negative effects of untreated hypothyroidism on basal metabolic rate, body mass index, and cardiovascular risk. Additionally, we recommend measuring TH concentrations 3–4 months after the start of growth hormone treatment.

Patients with Central Hypothyroidism are Less Sufficiently Treated with Levothyroxine than Patients with Primary Hypothyroidism

BACKGROUND

Contrary to patients with hypothyroidism after radioiodine (HRI) or after thyroidectomy (HTh), patients with central hypothyroidism (CH) cannot rely on thyrotropin (TSH) level to guide their treatment with L-thyroxine (L-T4). Consequently, they are at constant risk of under- or overtreatment. We aimed to establish the adequacy of L-T4 treatment in patients with CH in our cohort.

METHODS

Consecutive patients with CH on L-T4 treatment were compared with patients adequately treated for HRI or HTh. Levels of free thyroxine (fT₄) and free triiodothyronine (fT₃) were evaluated and the fT₄/fT₃ ratio was calculated.

RESULTS

Forty patients with CH, 136 patients with HRI and 43 patients with HTh were included in this study. Patients with HRI were significantly younger than patients with HTh and CH (p<0.001 for both). Levels of fT₄ were significantly lower in CH than in adequately treated patients with HRI and HTh (median (range), 15.6 (12.7-21.3), 18.4 (12.2-28.8), and 18.7 (13.8-25.5) pmol/L, respectively, p<0.001 for both comparisons). Levels of fT₃ did not differ significantly (p=0.521) between CH, HRI and HTh (median (range), 4.5 (2.7-5.9), 4.3 (3.2-6.2), and 4.4 (2.9-5.5) pmol/L, respectively). Accordingly, the fT₄/fT₃ ratio was significantly lower in the CH group than in HRI and HTh groups (median (range), 3.7 (2.5-5.2), 4.2 (1.2-7.7), and 4.4 (2.5-6.1), respectively, p<0.001 for both comparisons).

CONCLUSIONS

Patients with CH have lower fT₄ levels and lower fT₄/fT₃ ratios than patients adequately treated for HRI or HTh. The cause for this difference may be the unreliable TSH levels in patients with CH.

Mirtazapine use may increase the risk of hypothyroxinaemia in patients affected by major depressive disorder

AIMS

Hypothyroxinaemia could be easily neglected if attention is paid only to patients with elevated thyroid-stimulating hormone. We aimed to assess the association between mirtazapine use and hypothyroxinaemia in patients affected by major depressive disorder.

METHODS

We conducted a retrospective cohort study in the Second Affiliated Hospital of Xinxiang Medical University between January 2016 and December 2018. Patients affected by major depression disorder and admitted to the hospital for treatment during the study period and who had thyroid tests at admission and after treatment were included. Mirtazapine use during hospitalization was the exposure measure and newly developed hypothyroxinaemia was as the primary outcome and structure parameters of thyroid homeostasis were the secondary outcomes of this study. Log-binomial model was used to estimate the association between mirtazapine use and hypothyroxinaemia, after adjusting for potential confounding factors.

RESULTS

A total of 220 eligible patients were included in the final analysis. The incidence of hypothyroxinaemia in patients who used mirtazapine was higher (37.5%) than those patients who did not use (19.7%). The relative risk of developing hypothyroxinaemia was 1.70 (95% confidence interval: 1.21-2.43) for mirtazapine use, after adjusting for confounding factors. The degree of reduction in thyroid feedback quantile-based index in mirtazapine group was significantly greater than that in nonmirtazapine group.

CONCLUSION

Mirtazapine use was associated with the increased risk of developing hypothyroxinaemia. The underlying mechanism may be involved the changed central set point of thyroid homeostasis, in which pituitary was in a possibly impaired sensitivity to the lower level of thyroid hormones.

Rare Diseases of Larynx, Trachea and Thyroid

This review article covers data on rare diseases of the larynx, the trachea and the thyroid. In particular, congenital malformations, rare manifestations of inflammatory laryngeal disorders, benign and malignant epithelial as well as non-epithelial tumors, laryngeal and tracheal manifestations of general diseases and, finally, thyroid disorders are discussed. The individual chapters contain an overview of the data situation in the literature, the clinical appearance of each disorder, important key points for diagnosis and therapy and a statement on the prognosis of the disease. Finally, the authors indicate on study registers and self-help groups.

USE OF THE FREE THYROXINE INDEX TO REFINE THE LOWER LIMIT OF A FREE THYROXINE IMMUNOASSAY FOR DETECTION OF SECONDARY HYPOTHYROIDISM

OBJECTIVE

To determine the utility of measuring free T4 index (FT4I) in patients with low free T4 (FT4) levels using immunoassay and normal thyroid-stimulating hormone for the evaluation of secondary hypothyroidism.

METHODS

We performed a retrospective medical chart review of patients seen at a single institution as outpatients who had a simultaneously normal thyroid-stimulating hormone level, low FT4 level, and any FT4I measured between June 2014 and October 2016. Demographic, laboratory, and imaging data were collected. Using FT4I as the reference for diagnosis of hypothyroidism, the sensitivity and specificity of the FT4 immunoassay's lower-limit thresholds were determined. Within each threshold group, available brain imaging and biochemical evaluation were categorized according to the presence or absence of pituitary disease.

RESULTS

A total of 155 sets of result pairs (FT4 and FT4I) performed on 118 subjects were analyzed. The lower limit of a normal FT4 level by immunoassay at this institution was 0.93 ng/dL, though all pairs with FT4 ≥0.89 ng/dL had a normal FT4I. All pairs with FT4 ≤0.67 ng/dL had a low FT4I. No pituitary macroadenomas were identified in any subject, though the rates of pituitary imaging in this patient sample were low.

CONCLUSION

Patients with a borderline low FT4 level by immunoassay often have normal FT4I. In such patients at our center, significant structural and biochemical pituitary pathology was uncommon.

Prevalence of Hypothyroidism in Patients With Erdheim-Chester Disease

IMPORTANCE

Erdheim-Chester disease (ECD) is a rare non-Langerhans cell histiocytosis affecting multiple organs and commonly caused by somatic pathogenic variants in BRAF V600E and mitogen-activated protein kinase genes. Clinical features of ECD result from histiocytic involvement of various tissues; while endocrine involvement in ECD occurs frequently, the prevalence of central or primary hypothyroidism has not been thoroughly investigated.

OBJECTIVE

To assess hypothalamus-pituitary-thyroid (HPT) dysfunction in patients with ECD.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional study included 61 patients with ECD who were enrolled in a natural history study at a tertiary care center between January 2011 and December 2018. ECD was diagnosed on the basis of clinical, genetic, and histopathological features. Data were analyzed in March 2020.

EXPOSURE

Diagnosis of ECD.

MAIN OUTCOMES AND MEASURES

Main outcome was the prevalence of thyroid dysfunction in adults with ECD compared with community estimates. Patients underwent baseline evaluation with a thyroid function test, including thyrotropin, free thyroxine (fT4), and total thyroxine (T4), and sellar imaging with magnetic resonance imaging or computed tomography scan. The association of HPT dysfunction was assessed for differences in age, sex, body mass index, BRAF V600E status, high sensitivity C-reactive protein level, sellar imaging, and pituitary hormonal dysfunction.

RESULTS

A total of 61 patients with ECD (46 [75%] men; mean [SD] age, 54.3 [10.9] years) were evaluated. Seventeen patients (28%) had hypothyroidism requiring levothyroxine therapy. The prevalence of both central and primary hypothyroidism were higher than community estimates (central hypothyroidism: 9.8% vs 0.1%; odds ratio, 109.0; 95% CI, 37.4-260.6; P < .001; primary hypothyroidism: 18.0% vs 4.7%; OR, 4.4; 95% CI, 2.1-8.7; P < .001). Patients with hypothyroidism (both primary and central), compared with patients with euthyroidism, had higher body mass index (median [interquartile range] 31.4 [28.3-38.3] vs 26.7 [24.4-31.9]; P = .004) and a higher prevalence of panhypopituitarism (7 [47%] vs 3 [7%]; P < .001). Among patients with hypothyroidism, those with central hypothyroidism, compared with patients with primary hypothyroidism, had a lower mean (SD) body mass index (28.3 [2.6] vs 36.3 [5.9]; P = .007) and higher frequencies of abnormal sellar imaging (5 [83%] vs 3 [27%]; P = .050) and panhypopituitarism (5 [83%] vs 3 [27%]; P = .050).

CONCLUSIONS AND RELEVANCE

In this cohort study, a higher prevalence of central and primary hypothyroidism was identified in patients with ECD compared with the community. There should be a low threshold for testing for hypothyroidism in patients with ECD, and treatment should follow standard guidelines.

Long-term neuroendocrine consequences of traumatic brain injury and strategies for management

Introduction: Traumatic brain injuries (TBI) are reported to cause neuroendocrine impairment with a prevalence of 15% with confirmatory testing. Pituitary dysfunction (PD) may have detrimental effects on vital parameters as well as on body composition, cardiovascular functions, cognition, and quality of life. Therefore, much effort has been made to identify predictive factors for post-TBI PD and various screening strategies have been offered.Areas covered: We searched PubMed and reviewed the recent data on clinical perspectives and long-term outcomes as well as predictive factors and screening modalities of post-TBI PD. Inconsistencies in the literature are overviewed and new areas of research are discussed.Expert opinion: Studies investigating biomarkers that will accurately predict TBI patients with a high risk of PD are generally pilot studies with a small number of participants. Anti-pituitary and anti-hypothalamic antibodies, neural proteins, micro-RNAs are promising in this field. As severity of TBI has been the most commonly associated risk factor for post-TBI PD, we suggest prospective screening based on severity of head trauma until new evidence emerges. There is also a need for more studies investigating the clinical effects of hormone replacement in TBI patients with PD.

The "slightly" abnormal thyroid test: What is the pediatrician to do?

Thyroid disorders are common in pediatrics. Tests of thyroid function are widely available and frequently ordered in the pediatric healthcare setting. This is sometimes driven by common signs or symptoms of thyroid disease. All too often, it is driven by patients and their parents requesting thyroid tests for nonspecific symptoms, such as fatigue, obesity or family history of thyroid disease. The decision to order thyroid tests, as well as which test(s) of thyroid function to order, deserves careful thought rather than a reflexive "thyroid panel" for every patient. Thyroid stimulating hormone (TSH) is the single most appropriate test of thyroid function when screening a pediatric or adolescent for thyroid disorders. Adding more tests only increases the likelihood that a minor (and often insignificant) abnormality will be found. These incidental abnormalities can create anxiety for the parent and child, and usually results in additional testing, referral to a pediatric endocrinologist, and further expense. This review will aim to guide the pediatric primary care provider on the choice of appropriate screening test(s) for acquired thyroid dysfunction in children and adolescents, as well as the proper interpretation of the test(s). Emphasis will be placed on the "slightly" abnormal thyroid screening test. Specific thyroid tests to be reviewed include TSH, (free) T4, (free) T3, and thyroid antibodies. Finally, this review will aim to guide decisions on follow-up, additional testing, and reasons for referral to a pediatric endocrinologist. Congenital hypothyroidism, including abnormalities on state newborn screening, will not be discussed.

Central hypothyroidism

Central hypothyroidism is a rare cause of hypothyroidism, consequence of various disorders affecting pituitary (secondary) or hypothalamus (tertiary hypothyroidism). Difficulties in the diagnosis and management of patients are due to the nontypical clinical picture, frequent combination with impaired function of other pituitary hormones, difficulties in laboratory assessment in high TSH levels or low - normal T4 free levels. Diagnosis is based on a confirmed decrease in the level of free T4 with a low or normal level of TSH. The standard treatment for hypothyroidism of any etiology remains monotherapy with levothyroxine, which allows to restore the euthyroid state in most patients. The criterion for the effectiveness of therapy is to maintain the level of T4 free in the upper half of the reference norm interval. The article presents a modern understanding of epidemiology, pathogenesis and strategies for managing patients with central hypothyroidism.

Endocrine Outcomes After Pituitary Surgery

Although removal of pituitary tumors yields excellent surgical outcomes, perturbations in the hypothalamic-pituitary axis are not uncommon. Careful assessment of postoperative hormone status with supplementation or further medical therapy is critical to successful outcomes. Although many centers routinely use perioperative steroids, they can be associated with worse outcomes in the absence of intact preoperative adrenal function or damage to the pituitary gland or stalk during surgery. Postoperative assessment of prolactin, cortisol, and growth hormone can be prognostic of surgical cure. Hormonal axes should be reevaluated routinely several weeks after surgery, because longitudinal monitoring is important for surgical and medical outcomes.

Thyroid Disorders in Homozygous β-Thalassemia: Current Knowledge, Emerging Issues and Open Problems

Changes in thyroid function and thyroid function tests occur in patients with β-thalassemia major (TM). The frequency of hypothyroidism in TM patients ranges from 4% to 29 % in different reports. The wide variation has been attributed to several factors such as patients’ genotype, age, ethnic heterogeneity, treatment protocols of transfusions and chelation, and varying compliance to treatment. Hypothyroidism is the result of primary gland failure or insufficient thyroid gland stimulation by the hypothalamus or pituitary gland. The main laboratory parameters of thyroid function are the assessments of serum thyroid-stimulating hor-mone (TSH) and serum free thyroxine (FT4). It is of primary importance to interpret these measurements within the context of the laboratory-specific normative range for each test. An elevated serum TSH level with a standard range of serum FT4 level is consistent with subclinical hypothyroidism. A low serum FT4 level with a low, or inappropriately normal, serum TSH level is consistent with secondary hypothyroidism. Doctors caring for TM patients most commonly encounter subjects with subclinical primary hypothyroidism in the second decade of life. Several aspects remain to be elucidated as the frequency of thyroid cancer and the possible existence of a relationship between thyroid dysfunction, on one hand, cardiovascular diseases, components of metabolic syndrome (insulin resistance) and hypercoagulable state, on the other hand. Further studies are needed to explain these emerging issues. Following a brief description of thyroid hormone regulation, production and actions, this article is conceptually divided into two parts; the first reports the spectrum of thyroid disease occurring in patients with TM, and the second part focuses on the emerging issues and the open problems in TM patients with thyroid disorders.

Endocrine Diseases and the Liver: An Update

The endocrine system is a complex interconnected system of organs that control corporeal processes and function. Primary endocrine organs are involved in hormonal production and secretion but rely on a bevy of signals from the hypothalamic-pituitary axis and secondary endocrine organs, such as the liver. In turn, proper hepatic function is maintained through hormonal signaling. Thus, the endocrine system and liver are codependent, and diseases affecting either organs can lead to alterations in function within their counterparts. This article explores the hepato-endocrine relationship, including the effects on endocrine diseases on the liver.

Central Congenital Hypothyroidism Caused by a Novel Mutation, C47W, in the Cysteine Knot Region of TSHβ

BACKGROUND

Isolated central congenital hypothyroidism (ICCH) is a rare form (1:50,000 newborns) of congenital hypothyroidism, which can present with growth and neuropsychological retardation. Unlike the more common primary CH (1:1,500-1:4,000), which presents on newborn screening with elevated serum thyroid-stimulating hormone (TSH) and low thyroxine (T4) and triiodothyronine (T3), ICCH presents with low TSH and low thyroid hormone levels. ICCH, therefore, may be missed in most newborn screens that are based only on elevated TSH. Most cases of ICCH have been associated with mutations in the TSHβ gene.

PATIENT

We present a consanguineous Sudanese family where the proband was diagnosed with "atypical" CH (serum TSH was low, not high).

INTERVENTION AND OUTCOME

The propositus underwent whole-exome sequencing, and the C47W TSHβ mutation was identified. Sanger sequencing confirmed the proband to be homozygous for C47W, and both parents were heterozygous for the same mutation. The mutation was predicted by several in silico methods to have a deleterious effect (SIFT 0.0, Damaging; Polyphen2_HDIV 0.973, probably damaging; MutationTaster 1, disease causing; and CADD 3.17, 16.62). C47W affects the first cysteine of the cysteine knot of the TSHβ subunit. The cysteine knot region of TSHβ is highly conserved across species and is critical for binding to the TSH receptor. Only two other mutations were previously reported along the cysteine knot and showed consistently low or undetectable serum TSH and low T4 and T3 levels. Other TSHβ gene mutations causing ICCH have been reported in the "seatbelt" region, necessary for TSHβ dimerization with the alpha subunit.

CONCLUSIONS

Identification of a mutation in the TSHβ gene reinforces the importance of identifying ICCH that can occur in the absence of elevated serum TSH and demonstrates the functional significance of the TSHβ cysteine knot.

Less known aspects of central hypothyroidism: Part 1 - Acquired etiologies

Central hypothyroidism (CH) is a rare cause of hypothyroidism. CH is frequently overlooked, as its clinical picture is subtle and includes non-specific symptoms; furthermore, if measurement of TSH alone is used to screen for thyroid function, TSH concentrations can be normal or even above the upper normal reference limit. Indeed, certain patients are at risk of developing CH, such as those with a pituitary adenoma or hypophysitis, those who have been treated for a childhood malignancy, have suffered a head trauma, sub-arachnoid hemorrhage or meningitis, and those who are on drugs capable to reduce TSH secretion.

Subclinical hypothyroidism or central hypothyroidism-The danger of thyroid function misinterpretation

Correct interpretation of thyroid function tests is critical to providing appropriate care to patients with suspected thyroid disease. It is particularly important to distinguish central hypothyroidism from other types due to the potential of concurrent secondary adrenal insufficiency and thus the need for immediate steroid replacement prior to commencing thyroxine.

The frequency of hypothyroidism and its relationship with HCV positivity in patients with thalassemia major in southern Iran

INTRODUCTION

Hypothyroidism is one the most complication due to iron overload in patients with β-thalassemia major (TM). On the other hand these patients are prone to Hepatitis C virus (HCV) infection that can cause  thyroid dysfunction by itself or as the side effect of treatment with interferon (INF) or IFN plus ribavirin. The aim of this study is to evaluate the association of hypothyroidism with HCV positivity and serum ferritin levels in patients with TM.

METHODS

In this cross-sectional study, 201 randomly selected patients with TM who were registered at the Thalassemia Clinic of a tertiary hospital in Shiraz, southern Iran were investigated. Thyroid function tests and serologic screening assays for HCV seropositivity (HCV Ab and HCV-RNA) were conducted for all patients.

RESULTS

Frequency of hypothyroidism was 22.9% including 19.9% subclinical hypothyroidism, 2% primary overt hypothyroidism and 1% central hypothyroidism. Eighty six patients (42.8%) were HCV Ab positive and 60 patients (29.9%) were HCV RNA positive. No significant relationship was found between hypothyroidism and HCV positivity or receiving IFN-α (P>0.05). Hypothyroidism showed a borderline significant association with high serum ferritin levels in TM patients (P=0.055).

CONCLUSION

Our results showed no significant association between hypothyroidism and HCV infection in TM patients. It seems that the main mechanism of hypothyroidism in our patients is iron overload; however, for better evaluation a larger multicenter study is recommended.  Also due to the importance of consequences of HCV infection, more careful pre-transfusional screening of blood should be considered in TM patients.

Thyrotrophic status in patients with pituitary stalk interruption syndrome

Pituitary stalk interruption syndrome (PSIS) is associated with simultaneous or subsequent pituitary hormone deficiencies (PHDs). Although the clinical features of multiple PHDs are well known, the status of the thyrotrophic axis in PSIS has not been thoroughly investigated.The clinical data of 89 PSIS patients and 34 Sheehan syndrome (SS) patients were retrospectively analyzed.The prevalence of central hypothyroidism in the PSIS patients and the SS patients was 79.8% and 70.6%, respectively. The thyroid-stimulating hormone (TSH) levels in the PSIS patients were significantly higher in comparison with the SS patients (5.13 ± 3.40 vs 1.67 ± 1.20 mU/L, P < .05). TSH elevation (8.79 ± 3.17 mU/L) was noticed in 29 of 71 (40.85%) hypothyroid PSIS patients but not in the 24 hypothyroid SS patients. The TSH levels in the hypothyroid PSIS patients were significantly higher in comparison with the euthyroid PSIS patients (5.42 ± 3.67 vs 3.66 ± 1.50 mU/L). Thyroid hormone replacement significantly reduced the TSH levels in the PSIS patients with elevated TSH levels from 7.24 ± 0.98 to 1.67 ± 1.51 mU/L (P < .05). The logistic regression analysis suggested that TSH level was not significantly associated with pituitary stalk status and height of the anterior pituitary gland.PSIS is a newly recognized cause of central hypothyroidism. The proportion and amplitude of TSH elevations are higher in PSIS than in other causes of central hypothyroidism.

Lessons learnt from a case of missed central hypothyroidism

We present the case of a 57-year-old lady who had a delayed diagnosis of central hypothyroidism on a background of Grave's thyrotoxicosis and a partial thyroidectomy. During the twenty years following her partial thyroidectomy, the patient developed a constellation of symptoms and new diagnoses, which were investigated by numerous specialists from various fields, namely rheumatology, renal and respiratory. She developed significantly impaired renal function and raised creatine kinase (CK). She was also referred to a tertiary neurology service for investigation of myositis, which resulted in inconclusive muscle biopsies. Recurrently normal TSH results reassured clinicians that this did not relate to previous thyroid dysfunction. In 2015, she developed increased shortness of breath and was found to have a significant pericardial effusion. The clinical biochemist reviewed this lady's blood results and elected to add on a free T4 (fT4) and free T3 (fT3), which were found to be <0.4 pmol/L (normal range (NR): 12-22 pmol/L) and 0.3 pmol/L (NR: 3.1-6.8 pmol/L), respectively. She was referred urgently to the endocrine services and commenced on Levothyroxine replacement for profound central hypothyroidism. Her other pituitary hormones and MRI were normal. In the following year, her eGFR and CK normalised, and her myositis symptoms, breathlessness and pericardial effusion resolved. One year following initiation of Levothyroxine, her fT4 and fT3 were in the normal range for the first time. This case highlights the pitfalls of relying purely on TSH for excluding hypothyroidism and the devastating effect the delay in diagnosis had upon this patient.

Learning points

Isolated central hypothyroidism is very rare, but should be considered irrespective of previous thyroid disorders.If clinicians have a strong suspicion that a patient may have hypothyroidism despite normal TSH, they should ensure they measure fT3 and fT4.Laboratories that do not perform fT3 and fT4 routinely should review advice sent to requesting clinicians to include a statement explaining that a normal TSH excludes primary but not secondary hypothyroidism.Thyroid function tests should be performed routinely in patients presenting with renal impairment or a raised CK.

Regulatory aspects of the human hypothalamus-pituitary-thyroid axis

Thyroid hormones are essential for growth, differentiation and metabolism during prenatal and postnatal life. The hypothalamus-pituitary-thyroid (HPT)-axis is optimized for these actions. Knowledge of this hormonal axis is derived from decades of experiments in animals and man, and more recently from spontaneous mutations in man and constructed mutations in mice. This review examines the HPT-axis in relation to 24 h TSH profiles in men in various physiological and pathophysiological conditions, including obesity, age, longevity, and primary as well as central hypothyroidism. Hormone rhythms can be analyzed by quantitative methods, e.g. operator-independent deconvolution, approximate entropy and fitting the 24-h component by Cosinor analysis or related procedures. These approaches have identified some of the regulatory components in (patho)physiological conditions.

Central hypothyroidism - a neglected thyroid disorder

Central hypothyroidism is a rare and heterogeneous disorder that is characterized by a defect in thyroid hormone secretion in an otherwise normal thyroid gland due to insufficient stimulation by TSH. The disease results from the abnormal function of the pituitary gland, the hypothalamus, or both. Moreover, central hypothyroidism can be isolated or combined with other pituitary hormone deficiencies, which are mostly acquired and are rarely congenital. The clinical manifestations of central hypothyroidism are usually milder than those observed in primary hypothyroidism. Obtaining a positive diagnosis for central hypothyroidism can be difficult from both a clinical and a biochemical perspective. The diagnosis of central hypothyroidism is based on low circulating levels of free T₄ in the presence of low to normal TSH concentrations. The correct diagnosis of both acquired (also termed sporadic) and congenital (also termed genetic) central hypothyroidism can be hindered by methodological interference in free T₄ or TSH measurements; routine utilization of total T₄ or T₃ measurements; concurrent systemic illness that is characterized by low levels of free T₄ and normal TSH concentrations; the use of the sole TSH-reflex strategy, which is the measurement of the sole level of TSH, without free T₄, if levels of TSH are in the normal range; and the diagnosis of congenital hypothyroidism based on TSH analysis without the concomitant measurement of serum levels of T₄. In this Review, we discuss current knowledge of the causes of central hypothyroidism, emphasizing possible pitfalls in the diagnosis and treatment of this disorder.

TRH Action Is Impaired in Pituitaries of Male IGSF1-Deficient Mice

Loss-of-function mutations in the X-linked immunoglobulin superfamily, member 1 (IGSF1) gene cause central hypothyroidism. IGSF1 is a transmembrane glycoprotein of unknown function expressed in thyrotropin (TSH)-producing thyrotrope cells of the anterior pituitary gland. The protein is cotranslationally cleaved, with only its C-terminal domain (CTD) being trafficked to the plasma membrane. Most intragenic IGSF1 mutations in humans map to the CTD. In this study, we used CRISPR-Cas9 to introduce a loss-of-function mutation into the IGSF1-CTD in mice. The modified allele encodes a truncated protein that fails to traffic to the plasma membrane. Under standard laboratory conditions, Igsf1-deficient males exhibit normal serum TSH levels as well as normal numbers of TSH-expressing thyrotropes. However, pituitary expression of the TSH subunit genes and TSH protein content are reduced, as is expression of the receptor for thyrotropin-releasing hormone (TRH). When challenged with exogenous TRH, Igsf1-deficient males release TSH, but to a significantly lesser extent than do their wild-type littermates. The mice show similarly attenuated TSH secretion when rendered profoundly hypothyroid with a low iodine diet supplemented with propylthiouracil. Collectively, these results indicate that impairments in pituitary TRH receptor expression and/or downstream signaling underlie central hypothyroidism in IGSF1 deficiency syndrome.

Hypothyroidism risk compared among nine common bipolar disorder therapies in a large US cohort

OBJECTIVES

Thyroid abnormalities in patients with bipolar disorder (BD) have been linked to lithium treatment for decades, yet other drugs have been less well studied. Our objective was to compare hypothyroidism risk for lithium versus the anticonvulsants and second-generation antipsychotics commonly prescribed for BD.

METHODS

Administrative claims data on 24,574 patients with BD were analyzed with competing risk survival analysis. Inclusion criteria were (i) one year of no prior hypothyroid diagnosis nor BD drug treatment, (ii) followed by at least one thyroid test during BD monotherapy on lithium carbonate, mood-stabilizing anticonvulsants (lamotrigine, valproate, oxcarbazepine, or carbamazepine) or antipsychotics (aripiprazole, olanzapine, risperidone, or quetiapine). The outcome was cumulative incidence of hypothyroidism per drug, in the presence of the competing risk of ending monotherapy, adjusted for age, sex, physician visits, and thyroid tests.

RESULTS

Adjusting for covariates, the four-year cumulative risk of hypothyroidism for lithium (8.8%) was 1.39-fold that of the lowest risk therapy, oxcarbazepine (6.3%). Lithium was non-statistically significantly different from quetiapine. While lithium conferred a higher risk when compared to all other treatments combined as a group, hypothyroidism risk error bars overlapped for all drugs. Treatment (p = 3.86e-3), age (p = 6.91e-10), sex (p = 3.93e-7), and thyroid testing (p = 2.79e-87) affected risk. Patients taking lithium were tested for hypothyroidism 2.26-3.05 times more frequently than those on other treatments.

CONCLUSIONS

Thyroid abnormalities occur frequently in patients with BD regardless of treatment. Therefore, patients should be regularly tested for clinical or subclinical thyroid abnormalities on all therapies and treated as indicated to prevent adverse effects of hormone imbalances on mood.

Recent advances in central congenital hypothyroidism

Central congenital hypothyroidism (CCH) may occur in isolation, or more frequently in combination with additional pituitary hormone deficits with or without associated extrapituitary abnormalities. Although uncommon, it may be more prevalent than previously thought, affecting up to 1:16 000 neonates in the Netherlands. Since TSH is not elevated, CCH will evade diagnosis in primary, TSH-based, CH screening programs and delayed detection may result in neurodevelopmental delay due to untreated neonatal hypothyroidism. Alternatively, coexisting growth hormones or ACTH deficiency may pose additional risks, such as life threatening hypoglycaemia. Genetic ascertainment is possible in a minority of cases and reveals mutations in genes controlling the TSH biosynthetic pathway (TSHB, TRHR, IGSF1) in isolated TSH deficiency, or early (HESX1, LHX3, LHX4, SOX3, OTX2) or late (PROP1, POU1F1) pituitary transcription factors in combined hormone deficits. Since TSH cannot be used as an indicator of euthyroidism, adequacy of treatment can be difficult to monitor due to a paucity of alternative biomarkers. This review will summarize the normal physiology of pituitary development and the hypothalamic-pituitary-thyroid axis, then describe known genetic causes of isolated central hypothyroidism and combined pituitary hormone deficits associated with TSH deficiency. Difficulties in diagnosis and management of these conditions will then be discussed.

Do children with congenital hypothyroidism exhibit abnormal cortical morphology?

BACKGROUND

Given thyroid hormone (TH)'s essential role in multiple aspects of early brain development, children with congenital hypothyroidism (CH) detected and treated early may still display subtle cognitive and behavioral impairments as well as brain abnormalities. However, effects on their cortical development are not yet known. We used an automated neuroimaging technique to determine if these children differ in cortical thickness (CT) from typically developing controls (TDC) and if the regions showing CT differences reflect severity of initial hypothyroidism and predict later neuropsychological functioning.

METHODS

FreeSurfer Image Analysis Suite was used on archived MRI scans from 41 CH and 42 TDC children aged 9-16 y. Vertex-based procedures were used to compare groups and perform correlations between CT and indices of disease severity and neuropsychological outcome.

RESULTS

The CH group showed multiple regions of cortical thinning or cortical thickening within right and left hemispheres relative to TDC. CT values were significantly correlated with early T4 and thyroid-stimulating hormone (TSH) levels and current neuropsychological test indices.

CONCLUSION

The developing cortex is sensitive to early TH loss in CH. Different patterns of cortical thinning or cortical thickening among brain regions may reflect timing of TH deficiency relative to timing of cortical development.

Central hypothyroidism in adults: better understanding for better care

Central hypothyroidism (CH) is a rare cause of hypothyroidism generally related to a hypothalamic-pituitary disorder or arising as an iatrogenic complication. In adults, CH may be secondary to quantitative and/or qualitative alterations in thyroid-stimulating hormone (TSH) secretion. The disease is difficult to diagnose clinically because it lacks specific clinical signs and these may be masked by other anterior pituitary hormone secretion deficiencies. In patients with long-standing and marked CH, a diagnosis may be made based on low free T4 levels and normal, low or moderately increased TSH levels. In patients with early-stage or moderate CH, exploration of the circadian TSH cycle, determination of TSH response after a TRH test or recombinant TSH injection, estimation of TSH index, or evaluation of peripheral indexes of thyroid hormone metabolism may be required to establish a diagnosis. Regarding treatment, patients should receive levothyroxine replacement therapy, but hormone objectives during follow-up need to be precisely determined in order to reduce cardiovascular risks and to improve the quality of life of patients.

Guidelines for the treatment of hypothyroidism: prepared by the american thyroid association task force on thyroid hormone replacement

BACKGROUND

A number of recent advances in our understanding of thyroid physiology may shed light on why some patients feel unwell while taking levothyroxine monotherapy. The purpose of this task force was to review the goals of levothyroxine therapy, the optimal prescription of conventional levothyroxine therapy, the sources of dissatisfaction with levothyroxine therapy, the evidence on treatment alternatives, and the relevant knowledge gaps. We wished to determine whether there are sufficient new data generated by well-designed studies to provide reason to pursue such therapies and change the current standard of care. This document is intended to inform clinical decision-making on thyroid hormone replacement therapy; it is not a replacement for individualized clinical judgment.

METHODS

Task force members identified 24 questions relevant to the treatment of hypothyroidism. The clinical literature relating to each question was then reviewed. Clinical reviews were supplemented, when relevant, with related mechanistic and bench research literature reviews, performed by our team of translational scientists. Ethics reviews were provided, when relevant, by a bioethicist. The responses to questions were formatted, when possible, in the form of a formal clinical recommendation statement. When responses were not suitable for a formal clinical recommendation, a summary response statement without a formal clinical recommendation was developed. For clinical recommendations, the supporting evidence was appraised, and the strength of each clinical recommendation was assessed, using the American College of Physicians system. The final document was organized so that each topic is introduced with a question, followed by a formal clinical recommendation. Stakeholder input was received at a national meeting, with some subsequent refinement of the clinical questions addressed in the document. Consensus was achieved for all recommendations by the task force.

RESULTS

We reviewed the following therapeutic categories: (i) levothyroxine therapy, (ii) non-levothyroxine-based thyroid hormone therapies, and (iii) use of thyroid hormone analogs. The second category included thyroid extracts, synthetic combination therapy, triiodothyronine therapy, and compounded thyroid hormones.

CONCLUSIONS

We concluded that levothyroxine should remain the standard of care for treating hypothyroidism. We found no consistently strong evidence for the superiority of alternative preparations (e.g., levothyroxine-liothyronine combination therapy, or thyroid extract therapy, or others) over monotherapy with levothyroxine, in improving health outcomes. Some examples of future research needs include the development of superior biomarkers of euthyroidism to supplement thyrotropin measurements, mechanistic research on serum triiodothyronine levels (including effects of age and disease status, relationship with tissue concentrations, as well as potential therapeutic targeting), and long-term outcome clinical trials testing combination therapy or thyroid extracts (including subgroup effects). Additional research is also needed to develop thyroid hormone analogs with a favorable benefit to risk profile.

Treatment with thyroid hormone

Thyroid hormone deficiency can have important repercussions. Treatment with thyroid hormone in replacement doses is essential in patients with hypothyroidism. In this review, we critically discuss the thyroid hormone formulations that are available and approaches to correct replacement therapy with thyroid hormone in primary and central hypothyroidism in different periods of life such as pregnancy, birth, infancy, childhood, and adolescence as well as in adult patients, the elderly, and in patients with comorbidities. Despite the frequent and long term use of l-T4, several studies have documented frequent under- and overtreatment during replacement therapy in hypothyroid patients. We assess the factors determining l-T4 requirements (sex, age, gender, menstrual status, body weight, and lean body mass), the major causes of failure to achieve optimal serum TSH levels in undertreated patients (poor patient compliance, timing of l-T4 administration, interferences with absorption, gastrointestinal diseases, and drugs), and the adverse consequences of unintentional TSH suppression in overtreated patients. Opinions differ regarding the treatment of mild thyroid hormone deficiency, and we examine the recent evidence favoring treatment of this condition. New data suggesting that combined therapy with T3 and T4 could be indicated in some patients with hypothyroidism are assessed, and the indications for TSH suppression with l-T4 in patients with euthyroid multinodular goiter and in those with differentiated thyroid cancer are reviewed. Lastly, we address the potential use of thyroid hormones or their analogs in obese patients and in severe cardiac diseases, dyslipidemia, and nonthyroidal illnesses.

Thyrotropin isoforms: implications for thyrotropin analysis and clinical practice

Serum thyrotropin (TSH) is considered the single most sensitive and specific measure of thyroid function in the general population owing to its negative logarithmic association with free triiodothyronine and free thyroxine concentrations. It is therefore often the test of choice for screening, diagnosis, and monitoring of primary hypothyroidism. Serum TSH concentrations can be analyzed quantitatively using third-generation immunoassays, whereas its bioactivity can be measured by TSH activity assays in cell culture. Theoretically, if serum TSH concentrations are directly related to TSH activity, the two tests should yield comparable results. However, on occasion, the results are discordant, with serum concentrations being higher than TSH biological activity. This review focuses on the dissociation between the clinical state and serum TSH concentrations and addresses clinically important aspects of TSH analysis.

Thyrotropin secretion patterns in health and disease

Thyroid hormones are extremely important for metabolism, development, and growth during the lifetime. The hypothalamo-pituitary-thyroid axis is precisely regulated for these purposes. Much of our knowledge of this hormonal axis is derived from experiments in animals and mutations in man. This review examines the hypothalamo-pituitary-thyroid axis particularly in relation to the regulated 24-hour serum TSH concentration profiles in physiological and pathophysiological conditions, including obesity, primary hypothyroidism, pituitary diseases, psychiatric disorders, and selected neurological diseases. Diurnal TSH rhythms can be analyzed with novel and precise techniques, eg, operator-independent deconvolution and approximate entropy. These approaches provide indirect insight in the regulatory components in pathophysiological conditions.

Clinical review: Central hypothyroidism: pathogenic, diagnostic, and therapeutic challenges

CONTEXT

Central hypothyroidism (CH) is a particular hypothyroid condition due to an insufficient stimulation by TSH of an otherwise normal thyroid gland. This condition raises several challenges for clinicians; therefore, a review of the most relevant findings on CH epidemiology, pathogenesis, and clinical management has been performed.

METHODOLOGY

The relevant papers were selected by a PubMed search using appropriate key words.

MAIN FINDINGS

CH can be the consequence of various disorders affecting either the pituitary gland or the hypothalamus, but most frequently affecting both of them. CH is about 1000-fold rarer than primary hypothyroidism. Except for the neonatal CH due to biallelic TSHβ mutations, the thyroid hormone defect is rarely as profound as can be observed in some primary forms. In contrast with primary hypothyroidism, CH is most frequently characterized by low/normal TSH levels, and adequate thyroid hormone replacement is associated with the suppression of residual TSH secretion. Thus, CH often represents a clinical challenge because physicians cannot rely on the systematic use of the "reflex TSH strategy." The clinical management of CH is further complicated by the frequent combination with other pituitary deficiencies and their substitution.

Diagnostic and therapeutic challenges of acquired thyrotropic deficiency

The acquired thyrotropic deficiency (TD) is a hypothyroid condition due to an insufficient stimulation by thyrotropin (TSH) of an otherwise normal thyroid gland. This disease can be the consequence of disorders affecting either the pituitary gland or the hypothalamus, but most frequently both of them, and is generally called central hypothyroidism (CH). CH is about one thousand folds rarer than primary hypothyroidism (PH) and the thyroid hormone defect is often less severe than in primary forms. Differently to PH, the TD is most frequently characterized by low/normal TSH levels and thyroid hormone replacement is associated with the suppression of residual TSH secretion. Thus, CH diagnosis and management often represent a clinical challenge because physicians cannot rely on the systematic use of the reflex TSH determination. The clinical challenge of CH is further amplified by the frequent combination with other pituitary deficiencies.

Overt and subclinical hypothyroidism: who to treat and how

Hypothyroidism denotes deficient production of thyroid hormone by the thyroid gland and can be primary (abnormality in thyroid gland itself) or secondary/central (as a result of hypothalamic or pituitary disease). The term 'subclinical hypothyroidism' is used to define that grade of primary hypothyroidism in which there is an elevated thyroid-stimulating hormone (TSH) concentration in the presence of normal serum free thyroxine (T4) and triiodothyronine (T3) concentrations. Subclinical hypothyroidism may progress to overt hypothyroidism in approximately 2-5% cases annually. All patients with overt hypothyroidism and subclinical hypothyroidism with TSH >10 mIU/L should be treated. There is consensus on the need to treat subclinical hypothyroidism of any magnitude in pregnant women and women who are contemplating pregnancy, to decrease the risk of pregnancy complications and impaired cognitive development of the offspring. However, controversy remains regarding treatment of non-pregnant adult patients with subclinical hypothyroidism and serum TSH values ≤10 mIU/L. In this subgroup, treatment should be considered in symptomatic patients, patients with infertility, and patients with goitre or positive anti-thyroid peroxidase (TPO) antibodies. Limited evidence suggests that treatment of subclinical hypothyroidism in patients with serum TSH of up to 10 mIU/L should probably be avoided in those aged >85 years. Other pituitary hormones should be evaluated in patients with central hypothyroidism, especially assessment of the hypothalamic-pituitary-adrenal axis, since hypocortisolism, if present, needs to be rectified prior to initiating thyroid hormone replacement. Levothyroxine (LT4) monotherapy remains the current standard for management of primary, as well as central, hypothyroidism. Treatment can be started with the full calculated dose for most young patients. However, treatment should be initiated at a low dose in elderly patients, patients with coronary artery disease and patients with long-standing severe hypothyroidism. In primary hypothyroidism, treatment is monitored with serum TSH, with a target of 0.5-2.0 mIU/L. In patients with central hypothyroidism, treatment is tailored according to free or total T4 levels, which should be maintained in the upper half of the normal range for age. In patients with persistently elevated TSH despite an apparently adequate replacement dose of LT4, poor compliance, malabsorption and the presence of drug interactions should be checked. Over-replacement is common in clinical practice and is associated with increased risk of atrial fibrillation and osteoporosis, and hence should be avoided.

Central hypothyroidism in a patient with pituitary autoimmunity: evidence for TSH-independent thyroid hormone synthesis

CONTEXT

Acquired central hypothyroidism is rare, especially when isolated, and is typically associated with detectable, although biologically inactive, serum TSH.

OBJECTIVE

We describe a 56-yr-old woman with profound central hypothyroidism and partial central hypoadrenalism, in the absence of other endocrine abnormalities. In contrast to most cases of central hypothyroidism, serum TSH remained undetectable for 9 months before the initiation of thyroid hormone and hydrocortisone treatment. A test for pituitary autoantibody was moderately positive. Serum free T(4), serum T(3), and neck radioiodine uptake were low but detectable. The thyroid and pituitary glands appeared morphologically normal on neck ultrasound and head magnetic resonance imaging, respectively.

SETTINGS

The study was conducted in a tertiary academic medical center.

CONCLUSIONS

This case illustrates the variable clinical presentation of pituitary autoimmunity. The persistence of low but detectable thyroid hormone levels and radioiodine neck uptake in the absence of TSH suggests that significant TSH-independent thyroid hormone synthesis may occur in the normal thyroid.

Free thyroxine level in the high normal reference range prescribed for nonpregnant women may reduce the preterm delivery rate in multiparous

Preterm birth is the most common reason for perinatal morbidity and mortality in the western world. It has been shown that in euthyreotic pregnant women with thyroid autoimmune antibodies, L-Thyroxine replacement reduces preterm delivery rate in singleton pregnancies. We investigated in a nonrandomized retrospective observational study whether L-Thyroxine replacement, maintaining maternal free thyroxine serum level in the high normal reference range prescribed for nonpregnant women also influences the rate of preterm delivery in women without thyroid autoimmune antibodies. As control group for preterm delivery rate, data from perinatal statistics of the State of Baden-Württemberg from 2006 were used. The preterm delivery rate in the study group was significantly reduced. The subgroup analysis shows no difference in primiparous but a decline in multiparous by approximately 61% with L-Thyroxine replacement. Maintaining free thyroxine serum level in the high normal reference range prescribed for nonpregnant women may reduce the preterm delivery rate.

Thyroid hormones as modulators of immune activities at the cellular level

BACKGROUND

Increasing evidence suggests that thyroid hormones, L-thyroxine (T(4)) and 3,3',5-triiodo-L-thyronine (T(3)), are modulators of the immune response. In monocytes, macrophages, leukocytes, natural killer cells, and lymphocytes, a wide range of immune functions such as chemotaxis, phagocytosis, generation of reactive oxygen species (ROS), and cytokine synthesis and release are altered under hypo- and hyperthyroid conditions.

SUMMARY

Hyperthyroidism decreases the proinflammatory activities of monocytes and macrophages, whereas enhancement of phagocytosis and increased levels of ROS may occur during hypothyroidism. The expression of proinflammatory molecules such as macrophage inflammatory protein-1α and interleukin-1β increases in hypothyroidism. However, in Kupffer cells, proinflammatory activities such as the respiratory burst, nitric oxide synthase activity, and tumor necrosis factor-α expression may result from increased T(3) levels. Thyroid hormones also affect natural killer cell activity and cell-mediated immune responses. Still, for many immune cells no clear correlation has been found so far between abnormally high or low T(3) or T(4) levels and the effects observed on the immune responses.

CONCLUSIONS

In this review we outline the contributions of thyroid hormones to different aspects of innate and adaptive immune responses. The relationship between thyroid hormones and immune cells is complex and T(3) and T(4) may modulate immune responses through both genomic and nongenomic mechanisms. Future studies of the molecular signaling mechanisms involved in this cross-talk between thyroid hormones and the immune system may support development of new strategies to improve clinical immune responses.

Central hypothyroidism

Central hypothyroidism is defined as hypothyroidism due to insufficient stimulation by thyroid stimulating hormone (TSH) of an otherwise normal thyroid gland. It has an estimated prevalence of approximately 1 in 80,000 to 1 in 120,000. It can be secondary hypothyroidism (pituitary) or tertiary hypothyroidism (hypothalamus) in origin. In children, it is usually caused by craniopharyngiomas or previous cranial irradiation for brain tumors or hematological malignancies. In adults, it is usually due to pituitary macroadenomas, pituitary surgeries or post-irradiation. Fatigue and peripheral edema are the most specific clinical features. Diagnosis is established by the presence of normal to low-normal TSH on the background of low-normal thyroid hormones, confirmed by the thyrotropin releasing hormone stimulation test. Therapy includes use of levothyroxine titrated to improvement in symptomology and keeping free T4 in the upper limit of normal reference range.