Reversible pituitary enlargement in the syndrome of resistance to thyroid hormone

Cardiovascular morbidity and mortality in patients in Wales, UK with resistance to thyroid hormone β (RTHβ): a linked-record cohort study

BACKGROUND

Individuals with resistance to thyroid hormone owing to mutations in the thyroid hormone receptor β gene (RTHβ) exhibit impaired tissue sensitivity to thyroid hormones, but retain sensitivity in cardiac tissue. Long-term health and survival outcomes in this rare disorder have not been evaluated. We investigated all-cause mortality and cardiovascular event risk in a cohort of patients with RTHβ, followed-up in UK endocrine clinics.

METHODS

In a retrospective cohort design, we linked genetically confirmed patients with RTHβ and age-matched and sex-matched population controls to outcomes in datasets within the Welsh Secure Anonymised Information Linkage (SAIL) Databank. Kaplan-Meier and Cox regression models analysed associations of RTHβ with all-cause mortality and cardiovascular events.

FINDINGS

We identified 61 patients with a genetic diagnosis of RTHβ between Jan 1, 1997, and Dec 31, 2019, and matched them with 2750 controls. Compared with controls, patients exhibited increased risks for all-cause mortality (hazard ratio [HR] 2·84, 95% CI 1·59-5·08), atrial fibrillation (10·56, 4·72-23·63), heart failure (HR 6·35, 95% CI 2·26-17·86), and major adverse cardiovascular events (MACE), comprising cardiovascular death, acute myocardial infarction, heart failure, or strokes (HR 3·49, 95% CI 2·04-5·99). The median age of first occurrence of any adverse event was 11 years earlier in patients (56 years, 95% CI 44-65) compared with controls (67 years, 65-70). Cubic spline analyses showed positive associations between FT4 concentrations at diagnosis and mortality or MACE, with FT4 concentration of 30 pmol/L or greater conferring increased risk. Compared with no intervention, treatment with antithyroid drugs, surgery or radioiodine gland ablation, or thyroxine did not control thyroid hormone excess.

INTERPRETATION

We have documented reduced survival and increased cardiovascular morbidity in a cohort of patients with RTHβ for the first time. These outcomes might be driven by lifelong cardiac exposure to thyroid hormone excess; and effective therapies, targeting hormone resistant pathways, could potentially curtail this risk.

FUNDING

Royal College of Physicians, Wellcome Trust Investigator Award, and NIHR Cambridge Biomedical Research Centre.

Reduced pituitary size in subjects with mutations in the THRB gene and thyroid hormone resistance

BACKGROUND

Thyroid hormone action is mediated by two forms of thyroid hormone receptors (α, β) with differential tissue distribution. Thyroid hormone receptor β (TRβ) mutations lead to resistance to thyroid hormone action in tissues predominantly expressing the β form of the receptor (pituitary, liver). This study seeks to identify the effects of mutant TRβ on pituitary size.

METHODS

High-resolution 3D T1-weighted magnetic resonance images were acquired in 19 patients with RTHβ in comparison to 19 healthy matched controls. Volumetric measurements of the pituitary gland were performed independently and blinded by four different raters (two neuroradiologists, one neurologist, one neuroscientist).

RESULTS

Patients with mutant TRβ (resistance to thyroid hormone β, RTHβ) showed elevated free tri-iodothyronine/thyroxine levels with normal thyroid-stimulating hormone levels, whereas healthy controls showed normal thyroid hormone levels. Imaging revealed smaller pituitary size in RTHβ patients in comparison to healthy controls (F(1,35) = 7.05, P = 0.012, partial η2 = 0.17).

CONCLUSION

RTHβ subjects have impaired sensitivity to thyroid hormones, along with decreased size of the pituitary gland.

Pituitary hyperplasia mimicking thyrotropin-producing pituitary adenoma in the patient with resistance to thyroid hormone: a case report

The syndrome of inappropriate thyroid-stimulating hormone (TSH) secretion is characterized by high circulating thyroid hormone concentrations in the presence of non-suppressed TSH. After exclusion of the laboratory interference, TSH-secreting pituitary adenoma (TSHoma) or resistance to thyroid hormone-beta (RTH-β) should be suspected. The presence of a pituitary adenoma on the hypothalamic-pituitary imaging supports the diagnosis of TSHoma. However, the incidental findings of non-functioning pituitary adenomas may appear in patients with RTH-β. Abnormal MRI finding in the RTH-β patient also includes pituitary enlargement from thyrotroph hyperplasia. We herein reported a patient with inappropriate TSH secretion who has pituitary hyperplasia mimicking TSHoma. This case illustrates the diagnostic tests to distinguish an RTH-β from TSHoma.

DIAGNOSIS OF ENDOCRINE DISEASE: Diagnostic approach to TSH-producing pituitary adenoma

Thyrotropin (TSH)-secreting adenomas (TSHomas) are the rarest form of pituitary adenomas, and most endocrinologists will see few cases in a lifetime, if any. In most cases, the diagnostic approach is complicated and cases may be referred after being presented as a syndrome of inappropriate TSH secretion or as a pituitary mass. This review aims to cover the past, present and possible future diagnostic approaches to TSHomas, including different clinical presentations, laboratory assessment and imaging advances. The differential diagnoses will be discussed, as well as possible coexisting disorders. By evaluating the existing reports and reviews describing this rare condition, this review aims to present a clinically practical suggestion on the diagnosic workup for TSHomas, Major advances and scientific breakthroughs in the imaging area in recent years, facilitating diagnosis of TSHomas, support the belief that future progress within the imaging field will play an important role in providing methods for a more efficient diagnosis of this rare condition.

Homozygous Resistance to Thyroid Hormone β: Can Combined Antithyroid Drug and Triiodothyroacetic Acid Treatment Prevent Cardiac Failure?

Resistance to thyroid hormone β (RTHβ) due to homozygous THRB defects is exceptionally rare, with only five kindreds reported worldwide. Cardiac dysfunction, which can be life-threatening, is recognized in the disorder. Here we describe the clinical, metabolic, ophthalmic, and cardiac findings in a 9-year-old boy harboring a biallelic THRB mutation (R243Q), along with biochemical, physiologic, and cardiac responses to carbimazole and triiodothyroacetic acid (TRIAC) therapy. The patient exhibits recognized features (goiter, nonsuppressed thyroid-stimulating hormone levels, upper respiratory tract infections, hyperactivity, low body mass index) of heterozygous RTHβ, with additional characteristics (dysmorphic facies, winging of scapulae) and more markedly elevated thyroid hormone levels, associated with the homozygous form of the disorder. Notably, an older sibling with similar clinical features and probable homozygous RTHβ had died of cardiac failure at age 13 years. Features of early dilated cardiomyopathy in our patient prompted combination treatment with carbimazole and TRIAC. Careful titration of therapy limited elevation in TSH levels and associated increase in thyroid volume. Subsequently, sustained reduction in thyroid hormones with normal TSH levels was reflected in lower basal metabolic rate, gain of lean body mass, and improved growth and cardiac function. A combination of antithyroid drug and TRIAC therapy may prevent thyrotoxic cardiomyopathy and its decompensation in homozygous or even heterozygous RTHβ in which life-threatening hyperthyroid features predominate.

Thyrotropin-secreting pituitary adenomas: epidemiology, diagnosis, and management

Inappropriate secretion of TSH was first described in 1960 in a patient with evidence of hyperthyroidism and expanded sella on imaging. It was later found that a type of pituitary adenoma that secretes TSH (thyrotropinoma) was the underlying cause. The objective of the present review article is to summarize data on the epidemiology, pathogenesis, diagnosis, and management of thyrotropinomas. The prevalence of thyrotropinomas is lower than that of other pituitary adenomas. Early diagnosis is now possible thanks to the availability of magnetic resonance imaging and sensitive laboratory assays. As a corollary, many patients now present earlier in the course of their disease and have smaller tumors at the time of diagnosis. Treatment also has evolved over time. Transsphenoidal surgery is still considered definitive therapy. Meanwhile, radiation therapy, including radiosurgery, is effective in achieving tumor control in the majority of patients. In the past, radiation therapy was used as second line treatment in patients with residual or recurrent tumor after surgery. However, the availability of somatostatin analogs, which can lead to normalization of thyroid function as well as shrink these tumors, has led to an increase in the role of medical therapy in patients who are not in remission after pituitary surgery. In addition, dopamine agonists have shown some efficacy in the management of these tumors. Better understanding of the molecular pathogenesis of thyrotropinomas may lead to rationally designed therapies for patients with thyrotropinomas.

Characteristics of patients with late manifestation of resistance thyroid hormone syndrome: a single-center experience

Resistance to thyroid hormone (RTH) is a rare genetic disease caused by reduced tissue sensitivity to thyroid hormone. The hallmark of RTH is elevated serum levels of thyroid hormone with unsuppressed thyrotropin (TSH). However, the most common form of RTH results from minor defects in the ligand-binding domain or hinge domain of the TRβ gene, resulting in impaired T3-induced transcriptional activity, often showing mild presentation. Early diagnosis can be challenging. The objective of the current study was to characterize this specific group of RTH patients. This was a retrospective study. Patients diagnosed as RTH with TRβ mutations were enrolled in a single institute between 2004 and 2014. A total of 14 patients were diagnosed as RTH with mutation in THβ gene. The median age at diagnosis was 22.5 (IQR: 13.25-32.75). Goiter was the most common clinical finding. TSH was significantly elevated after TRH injection (median peak was 21.83 μIU/l, IQR: 13.59-31.48), 9.2-fold compared to the basal level. We found 10 mutations in TRβ gene, all located in the last four exons, and including one novel mutation, H271D. In vitro study found that H271D mutation reduced TR affinity to T3. Four patients with intact thyroid were diagnosed after 16 years old, defined as late manifestation. Compared to those diagnosed before 10 years old, patients with late manifestation presented with normal growth and mental development. Interestingly, three of them carried R438H mutation. We identified a novel p.H271D mutation in TRβ associated with RTH. Endocrinologists should be alert that RTH is frequently found in euthyroid patients with mild symptoms and often leads to misleading diagnosis as well as inappropriate treatment.

Pitfalls in the measurement and interpretation of thyroid function tests

Thyroid function tests (TFTs) are amongst the most commonly requested laboratory investigations in both primary and secondary care. Fortunately, most TFTs are straightforward to interpret and confirm the clinical impression of euthyroidism, hypothyroidism or hyperthyroidism. However, in an important subgroup of patients the results of TFTs can seem confusing, either by virtue of being discordant with the clinical picture or because they appear incongruent with each other [e.g. raised thyroid hormones (TH), but with non-suppressed thyrotropin (TSH); raised TSH, but with normal TH]. In such cases, it is important first to revisit the clinical context, and to consider potential confounding factors, including alterations in normal physiology (e.g. pregnancy), intercurrent (non-thyroidal) illness, and medication usage (e.g. thyroxine, amiodarone, heparin). Once these have been excluded, laboratory artefacts in commonly used TSH or TH immunoassays should be screened for, thus avoiding unnecessary further investigation and/or treatment in cases where there is assay interference. In the remainder, consideration should be given to screening for rare genetic and acquired disorders of the hypothalamic-pituitary-thyroid (HPT) axis [e.g. resistance to thyroid hormone (RTH), thyrotropinoma (TSHoma)]. Here, we discuss the main pitfalls in the measurement and interpretation of TFTs, and propose a structured algorithm for the investigation and management of patients with anomalous/discordant TFTs.

TSH-Secreting Pituitary Macroadenoma in a Girl with Lingual Thyroid

Patients with long-standing hypothyroid are, in some cases, reported to develop pituitary gland hyperplasia due to loss of feedback inhibition of thyroxine in hypothalamus—the condition of which typically regresses after thyroxine replacement. Herein, a 15-year-old girl—with long-standing untreated lingual hypothyroid—presents with a pathologically proven TSH pituitary macroadenoma and bilateral large ovarian cysts. Although MR imaging may differentiate between hyperplasia and macroadenoma of the pituitary gland, pathological examination is still a cornerstone to correct diagnosis.

Resistance to thyroid hormone associated with a novel mutation of the thyroid β receptor gene in a four-year-old female

Resistance to thyroid hormone (RTH) is a rare syndrome of reduced responsiveness of target tissues to thyroid hormone and is caused mutation in the thyroid β receptor gene. We report a novel mutation, E445X, causing RTH in a 4-year old girl. The patient exhibited extreme signs and symptoms of RTH at an early age, and had a large compressive goiter. Following total extracapsular thyroidectomy, upper airway compression was relieved and symptoms of hyperthyroidism improved. This case appears to be the youngest child recorded to have undergone total thyroidectomy for RTH. Post-operative TSH elevations were managed with every-other-day triiodothyronine therapy.

What should be done when thyroid function tests do not make sense?

Interpretation of thyroid function tests (TFTs) is generally straightforward. However, in a minority of contexts the results of thyroid hormone and thyrotropin measurements either conflict with the clinical picture or form an unusual pattern. In many such cases, reassessment of the clinical context provides an explanation for the discrepant TFTs; in other instances, interference in one or other laboratory assays can be shown to account for divergent results; uncommonly, genetic defects in the hypothalamic-pituitary-thyroid axis are associated with anomalous TFTs. Failure to recognize these potential 'pitfalls' can lead to misdiagnosis and inappropriate management. Here, focusing particularly on the combination of hyperthyroxinaemia with nonsuppressed thyrotropin, we show how a structured approach to investigation can help make sense of atypical TFTs.

Atypical thyrotropin-secreting pituitary microadenoma revealed by severe osteoporosis in a young man

For 10 years, a young man was followed for a severe osteoporosis associated with a considerable reduction in height and a massive weight loss. The constant increase of signs of tissue impregnation with thyroid hormones and the molar ratios of alpha-TSH suggested an inappropriate secretion of thyrotropin. Magnetic resonance imaging finally revealed a thyrotropic microadenoma of the pituitary gland. This case gives some new additional information on thyrotropin-induced osteoporosis. To our knowledge such a case has never been reported in the literature.

Thyroid hormone resistance and pituitary enlargement after thyroid ablation in a woman on levothyroxine treatment

We report a patient with inappropriate secretion of thyrotropin (TSH) and a pituitary mass. Although she had been treated for biochemical hyperthyroidism with thyroid surgery and radioiodine ablation, she had never complained of specific symptoms or demonstrated signs of overt thyroid dysfunction. On evaluation, she had increased free thyroxine and TSH levels, normal serum glycoprotein alpha-subunit levels, and a significant TSH over-response to exogenous thyrotropin-releasing hormone stimulation. Magnetic resonance imaging with gadolinium enhancement showed a pituitary enlargement with suprasellar extension. An indium In 111 pentetreotide scan showed an abnormal focus of radionuclide accumulation in the pituitary area. Sequencing of the TRbeta gene showed that the patient was heterozygous for a new single nucleotide substitution resulting in the replacement of the normal arginine with a serine at amino acid 320 (R320S). We review the difficulties encountered in establishing a correct diagnosis in patients with inappropriate secretion of TSH in combination with pituitary enlargement. Due to its possible false-negative results, we do not recommend the use of indium In 111 pentetreotide as a tool in the differential diagnosis of inappropriate secretion of TSH.

Interferon-induced hypothyroidism causing reversible pituitary enlargement

OBJECTIVE

To present the first reported case of interferon-induced hypothyroidism with radiographic confirmation of secondary pituitary hyperplasia.

METHODS

We describe the case of a woman with recurrent malignant melanoma, outline the details of her endocrine work-up, and illustrate the serial findings on magnetic resonance imaging of the head.

RESULTS

A 26-year-old woman underwent surgical excision of a melanoma of the left thigh and 10 years later had a second melanoma removed from her right knee. Metastatic work-up revealed evidence of tumor involvement in the cervical and mediastinal lymph nodes. After treatment with interferon for 1 year, persistent fatigue and menstrual irregularities led to the laboratory diagnosis of hypothyroidism, and magnetic resonance imaging revealed pituitary enlargement. Both her endocrinopathy and the pituitary hyperplasia resolved with discontinuation of the interferon treatment and with institution of thyroid replacement therapy.

CONCLUSION

Clinicians should be aware of the potential adverse effects of interferon therapy to avoid inappropriate diagnosis of a pituitary adenoma or metastatic lesion in patients with cancer who are treated with interferon. In addition, screening for hypothyroidism should be performed in patients receiving interferon.

Different responses to chronic somatostatin analogues in patients with central hyperthyroidism

OBJECTIVE

Central hyperthyroidism is mainly due to two different causes, TSH-secreting pituitary adenoma (TSH-oma) and resistance to thyroid hormone in its pituitary variant, i.e. patients presenting with signs and symptoms of hyperthyroidism (PRTH). Because therapeutic approach and the clinical follow-up are extremely different in these two disorders, a correct differential diagnosis is mandatory. Unfortunately, no definite pathognomonic tool is presently available and an extensive biochemical and instrumental workup is frequently needed in order to reach the correct diagnosis. Aim of the present study was to investigate the use of somatostatin analogues in the differential diagnosis between TSH-omas and PRTH, as well as the possible treatment of PRTH with these analogues.

DESIGN AND PATIENTS

Eight patients with TSH-oma and four with PRTH underwent the acute test with somatostatin analogue Octreotide (0.1 mg subcutaneously), as well as long-acting Octreotide-LAR (30 mg intramuscularly every 28 days) for two months.

MEASUREMENTS

Serum TSH, FT3 and FT4 were evaluated in basal condition, at time 0 and every hour for 6 h during acute test, and every 15 days for 2 months during chronic treatment.

RESULTS

During acute test, in both patients with PRTH and TSH-oma, a similar reduction in immunoreactive TSH and FT3 levels was observed, while no variations were found in FT4 concentrations. In contrast, during the administration of Octreotide-LAR, no significant variations of all tested parameters were observed in PRTH group, whereas FT3 and FT4 concentrations normalized or presented a significant reduction (> 30% of pretreatment values) in seven of eight patients with TSH-oma, despite minor variation of immunoreactive TSH levels.

CONCLUSIONS

Chronic administration of long-acting somatostatin analogues in patients with central hyperthyroidism caused a marked decrease of FT3 and FT4 levels in all patients but one with TSH-oma, while patients with PRTH did not respond at all. Thus, administration of long acting somatostatin analogues for at least 2 months can be useful in the differential diagnosis in problematic cases of central hyperthyroidism. Furthermore, the present findings exclude the possibility of a beneficial effect of chronic administration of somatostatin analogues in controlling thyrotoxic symptoms in PRTH patients.

Germline and somatic thyroid hormone receptor mutations in man

Thyroid hormone plays important roles in metabolism, growth, and differentiation. Germline mutations in thyroid hormone receptor beta (TRbeta) have been identified in many individuals with resistance to thyroid hormone (RTH), a syndrome of hyposensitivity to T3. However, it has become increasingly apparent that somatic mutations can also occur in individual tissues, and are associated with tumors and malignancies in man. Herein we review the occurrence and identification of germline and somatic TR mutations and characterization of their pathological effects on hormone resistance and tumorigenesis.

Aberrant alternative splicing of thyroid hormone receptor in a TSH-secreting pituitary tumor is a mechanism for hormone resistance

Patients with TSH-secreting pituitary tumors (TSHomas) have high serum TSH levels despite elevated thyroid hormone levels. The mechanism for this defect in the negative regulation of TSH secretion is not known. We performed RT-PCR to detect mutations in TRbeta from a surgically resected TSHoma. Analyses of the RT-PCR products revealed a 135-bp deletion within the sixth exon that encodes the ligand-binding domain of TRbeta2. This deletion was caused by alternative splicing of TRbeta2 mRNA, as near-consensus splice sequences were found at the junction site and no deletion or mutations were detected in the tumoral genomic DNA. This TRbeta variant (TRbeta2spl) lacked thyroid hormone binding and had impaired T3-dependent negative regulation of both TSHbeta and glycoprotein hormone alpha-subunit genes in cotransfection studies. Furthermore, TRbeta2spl showed dominant negative activity against the wild-type TRbeta2. These findings strongly suggest that aberrant alternative splicing of TRbeta2 mRNA generated an abnormal TR protein that accounted for the defective negative regulation of TSH in the TSHoma. This is the first example of aberrant alternative splicing of a nuclear hormone receptor causing hormonal dysregulation. This novel posttranscriptional mechanism for generating abnormal receptors may occur in other hormone-resistant states or tumors in which no receptor mutation is detected in genomic DNA.

A pituitary tumor in a patient with thyroid hormone resistance: a diagnostic dilemma

Resistance to thyroid hormone (RTH) is due to mutations in the beta-isoform of the thyroid hormone receptor (TR-beta). RTH patients display inappropriate secretion of thyrotropin-releasing hormone (TRH) from the hypothalamus and thyrotropin (TSH) from the anterior pituitary, despite elevated levels of thyroid hormone thyroxine (T4) and triiodothyronine (T3). Thyrotropin-secreting tumors are presumed to represent clonal expansion of abnormal cells. Because the diagnosis of TSH-secreting tumors tends to be delayed and curative surgical resection remains under 50%, early diagnosis is paramount. Current diagnostic strategies suggest that RTH patients are distinguishable from patients with TSH-secreting pituitary tumors by the use of standard laboratory tests and imaging. Here, we present a woman in whom the standard evaluation for inappropriate TSH secretion was insufficient to distinguish these entities. The patient had a low-normal TRH stimulation test and an unmeasurable alpha-glycoprotein subunit level; however, a pituitary magnetic resonance imaging (MRI) revealed an adenoma. More testing using a T3 suppression test supported a RTH diagnosis and a R438H mutation was found in the TR-beta gene. To our knowledge, this represents the first report of an apparently incidental pituitary adenoma in the setting of documented resistance to thyroid hormone. As such, it raises the question of whether RTH predisposes to pituitary hyperplasia and adenoma development.

[Thyroid hormone resistance syndromes: clinical aspects]

INTRODUCTION

Syndromes of resistance to thyroid hormone correspond to variable clinical states which are usually transmitted as autosomal dominant traits and characterized by the lack of sensitivity of target tissues to triiodothyronine (T3). The diagnosis has to be performed in order to offer an appropriate therapy.

CURRENT KNOWLEDGE AND KEY POINTS

Clinical states range between two extremes: the generalized form, with global euthyroidism, and the predominantly pituitary form, with thyrotoxicosis. Surprisingly, these various clinical situations are usually determined by the same genetic defect, i.e., an anomaly of one of the two alleles of the gene encoding the thyroid hormone receptor TR beta. High levels of circulating thyroid hormones in the presence of detectable thyroid stimulating hormone (TSH) levels is the characteristic biological feature. Pituitary thyreotropic adenoma, another etiology of inappropriate secretion of TSH, needs thus to be ruled out. No treatment is required in case of generalized resistance to thyroid hormone, whereas two specific drugs (TRIAC and D-T4) appear to be useful in the predominantly pituitary form.

FUTURE PROSPECTS AND PROJECTS

Mechanisms of resistance have been well documented, therefore allowing better understanding of T3 action on its nuclear receptor. Several transcriptional cofactors or corepressors have been identified and have to be investigated to explain the intriguing inter- and intra-familial, and even intra-individual, phenotypic variability. New insights should, furthermore, be gained from these studies to precisely determine how therapeutic agents work in resistance to thyroid hormone.