Difficulty in differentiating thyrotropin secreting pituitary microadenoma from pituitary-selective thyroid hormone resistance accompanied by pituitary incidentaloma

Challenging diagnosis of resistance to thyroid hormone in a patient with pituitary adenoma

The elevation of thyroid hormone with a normal or elevated thyroid-stimulation hormone (TSH) occurs uncommonly. This set a diagnosis challenge between TSH-secreting pituitary adenoma and resistance to thyroid hormone (RTH). We report a case of a young female patient with palpitations, with elevated thyroid hormone and non-suppressed TSH. TSH receptor antibody was undetectable. Thyroid ultrasound revealed mild heterogeneous goitre, and MRI revealed a microadenoma with 7.5 mm length in pituitary's left lobe. Pituitary hormones were within normal ranges. The thyrotropin-releasing hormone stimulation test showed normal TSH elevation, consistent with RTH. The genetic test revealed a mutation in heterozygosity in THRB gene (G344R) confirming RTH-beta. No pituitary surgery or thyroidectomy was performed nor were prescribed any antithyroid drugs. Inappropriate secretion of TSH requires a high level of clinical suspicion and the proper laboratory, genetic and radiological studies to conduct a correct diagnosis and prevent unnecessary and potential harmful therapies.

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.

Management of nonfunctioning pituitary incidentaloma

Prevalence of pituitary incidentaloma is variable: between 1.4% and 27% at autopsy, and between 3.7% and 37% on imaging. Pituitary microincidentalomas (serendipitously discovered adenoma <1cm in diameter) may increase in size, but only 5% exceed 10mm. Pituitary macroincidentalomas (serendipitously discovered adenoma>1cm in diameter) show increased size in 20-24% and 34-40% of cases at respectively 4 and 8years' follow-up. Radiologic differential diagnosis requires MRI centered on the pituitary gland. Initial assessment of nonfunctioning (NF) microincidentaloma is firstly clinical, the endocrinologist looking for signs of hypersecretion (signs of hyperprolactinemia, acromegaly or Cushing's syndrome), followed up by systematic prolactin and IGF-1 assay. Initial assessment of NF macroincidentaloma is clinical, the endocrinologist looking for signs of hormonal hypersecretion or hypopituitarism, followed up by hormonal assay to screen for hypersecretion or hormonal deficiency and by ophthalmologic assessment (visual acuity and visual field) if and only if the lesion is near the optic chiasm (OC). NF microincidentaloma of less than 5mm requires no surveillance; those of≥5mm are not operated on but rather monitored on MRI at 6months and then 2years. Macroincidentaloma remote from the OC is monitored on MRI at 1year, with hormonal exploration (for anterior pituitary deficiency), then every 2years. When macroincidentaloma located near the OC is managed by surveillance rather than surgery, MRI is recommended at 6months, with hormonal and visual exploration, then annual MRI and hormonal and visual assessment every 6months. Surgery is indicated in the following cases: evolutive NF microincidentaloma, NF macroincidentaloma associated with hypopituitarism or showing progression, incidentaloma compressing the OC, possible malignancy, non-compliant patient, pregnancy desired in the short-term, or context at risk of apoplexy.

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.

Incidentalomas hipofisários

Lesões hipofisárias clinicamente inaparentes são demonstradas através da ressonância magnética em aproximadamente 10% da população geral adulta, caracterizando os chamados incidentalomas hipofisários. A história natural dessas lesões ainda não está completamente estabelecida. Embora sejam tipicamente pequenos (< 10mm no seu maior diâmetro) e clinicamente silenciosos, alguns incidentalomas hipofisários podem secretar hormônios ou causar efeitos de massa por compressão sobre estruturas vizinhas. Além disso, uma minoria dessas lesões, principalmente aquelas com mais de 10mm (macroincidentalomas) podem crescer com o tempo; assim, o seguimento a longo prazo se faz necessário. Intervenções terapêuticas estão indicadas para os incidentalomas funcionantes (uso de agonistas dopaminérgicos ou ressecção transesfenoidal) ou para aqueles que causem efeitos de massa ou aumentem de tamanho durante o seguimento (ressecção transesfenoidal). Significante extensão supra-selar ou hipopituitarismo podem ser indicações adicionais para o tratamento cirúrgico, mesmo na ausência de compressão quiasmática.

Clinical and molecular features of a TSH-secreting pituitary microadenoma

We describe a case of a thyroid stimulating hormone (TSH)-secreting pituitary microadenoma, and report the systematic gene expression profile of the surgically- removed tumor. A 50-year-old woman was referred to our hospital because she had high TSH, free-T4, and free-T3 levels, and a pituitary tumor that was visualized with magnetic resonance imaging. Her basal TSH level was high even after a high T3 loading dose, and increased following administration of thyroid releasing hormone (TRH) even after administration of a high dose of exogenous T3. Her clinical symptoms and peripheral markers for T3 were responsive to exogenous T3. There was no thyroid hormone receptor (TR) beta gene mutation. The patient was diagnosed with a TSH-secreting pituitary adenoma, and trans-sphenoid surgery was performed. The histologic features and immunophenotype were consistent with a TSH-secreting pituitary adenoma. Reverse transcription-polymerase chain reaction analysis of pituitary hormones, pituitary-specific transcription factors, receptors, and transcriptional cofactors of clinical significance was performed on the removed tumor. The tumor expressed TSH, growth hormone, prolactin, alpha-subunit, pituitary transcription factor-1 (pit-1) but not proopiomelanocortin (POMC), prophet of pit-1 (prop-1) and pituitary cell-restricted T box factor (Tpit). TRbeta and TRH-receptor gene expression was normal. Three steroid receptor coactivators (SRC)-1, SRC-2, and SRC-3 were expressed. Nuclear receptor corepressor (N-CoR)2 was absent in the tumor, whereas nuclear receptor corepressor (N-CoR1) was expressed. Somatostatin receptor type 1 expression was significantly decreased, whereas type 4 receptor was expressed, which are unusual characteristics for pituitary tumors. The gene expression pattern in the tumor might have a role in the clinical features of this case.

Diagnostic and Therapeutic Approach to Pituitary Incidentalomas

OBJECTIVE

To review data on epidemiology, differential diagnosis, clinical, laboratory, and imaging findings, natural history, and management of incidentally discovered pituitary lesions (pituitary incidentalomas).

METHODS

A nonsystematic review was conducted, including articles indexed in Index Medicus that contained reference to incidentally discovered pituitary masses (pituitary incidentalomas).

RESULTS

Both autopsy and sensitive neuroimaging studies (including magnetic resonance imaging) suggest that pituitary incidentalomas are common, affecting approximately 10% of the general population. Although typically small (less than 10 mm in greatest diameter) and clinically silent, some pituitary incidentalomas may be hormonally active or cause mass effects by compressing neighboring structures. In addition, a minority of these lesions may grow over time; hence, long-term follow-up is necessary. Therapeutic interventions, including dopamine agonist therapy (in the case of prolactin-secreting adenomas) or transsphenoidal resection, are indicated in the case of pituitary lesions that are hormonally active, cause mass effects, or increase in size.

CONCLUSION

Pituitary incidentalomas are common and constitute a heterogeneous group with regard to pathologic features, clinical, laboratory, and imaging characteristics, natural history, and growth potential. Currently available evidence suggests that many hormonally nonfunctioning pituitary incidentalomas causing no mass effects can be safely managed by follow-up surveillance. Nonetheless, more data are needed for further elucidation of the natural history of these lesions and for improvement in accurate and noninvasive diagnosis and in prediction of growth potential of pituitary incidentalomas. Improved understanding of the pathogenesis of this heterogeneous group of lesions may also lead to the development of novel, noninvasive therapeutic agents, rationally designed to interact with well-characterized molecular targets.

Thyrotropin-secreting Pituitary Tumor and Hashimotoʼs Disease: A Novel Association

A 69-year-old man was referred for elevated thyroid hormone levels. He had no symptoms apart from mild hyperhidrosis and heat intolerance with occasional headaches. Past medical history included a right hemithyroidectomy for a multinodular goiter and Hashimoto's disease. At presentation the patient had a firm, slightly enlarged left thyroid lobe. There were no visual abnormalities, and the rest of the physical findings were unremarkable. Laboratory findings included elevated values of free T4, free T3, total T3, thyrotropin-secreting hormone (TSH), antithyroglobulin, and antimicrosomal antibodies. Normal values were found for cortisol, prolactin, testosterone, follicle-stimulating hormone, luteinizing hormone, alpha-subunit, and thyroid-stimulating immunoglobulin. Thyroid 123I scan showed an increased 5-hour uptake of 23% and a 24-hour uptake of 53% with a diffuse uniform enlargement of the left side. TSH level did not increase after a thyrotropin-releasing hormone stimulation test. Serum sex hormone binding globulin was elevated. Magnetic resonance imaging of the pituitary revealed a pituitary macroadenoma with suprasellar extension to the optic chiasm. Histologic examination of the adenoma after transsphenoidal hypophysectomy showed cells that stained positive for TSH. TSH-secreting pituitary adenomas account for 1% of functioning pituitary tumors and are an exceedingly rare cause of hyperthyroidism. To our knowledge, this is the first report of pituitary tumor inducing hyperthyroidism in the setting of Hashimoto's disease. There is a possibility that TSH elevation related to Hashimoto's disease might have contributed to the development of a TSH-secreting pituitary adenoma.

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.