The TSH secretion in the human pituitary adenomas

Diagnosis, pathology, and management of TSH-secreting pituitary tumors. A single-center retrospective study of 20 patients from 1981 to 2014

TSH (thyroid-stimulating hormone)-secreting tumors are the rarest type of pituitary tumor. The objective of this study was to describe initial presentation and follow-up in patients presenting TSH-secreting tumors and to characterize the pathological features, based on a cohort of 20 patients treated in our referral center, between 1981 and 2014. Most of the patients (75%) were female, aged around 50 years (mean: 50±13 years). Initial symptoms were hyperthyroidism (8/20) and/or tumor mass-related symptoms. Median time to diagnosis was 18 months. Biochemical hyperthyroidism was found in 15 patients. Most of the tumors were macroadenomas (75%) and 30% were invasive. Seventeen patients underwent transsphenoidal surgery. All tumors expressed TSH, with>50% positive cells. Eleven were monohormonal and 6 plurihormonal, expressing βTSH plus growth hormone (GH) and/or prolactin (PRL). Both subtypes showed high expression of Pit-1 and SSTR_2A somatostatin receptors. SSTR₅ was slightly expressed in the plurihormonal subtype. Ki-67 index was elevated (≥3%) in only one tumor. Signs of hyperthyroidism were more frequent in the plurihormonal than in the monohormonal subtype. At final follow-up (median: 34.79±66.7 months), 75% of the patients were in complete remission after surgery; persistent hyperthyroidism was controlled by somatostatin analogs, alone (n=3) or associated to radiotherapy (n=1). The multidisciplinary approach promoted early diagnosis and control of hyperthyroidism by neurosurgical treatment, associated to somatostatin analogs or not. Clinical/pathological correlations highlighted the variations in immune profiles and in clinical and biological symptoms.

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.

Subclinical hyperfunctioning pituitary adenomas: the silent tumors

Pituitary adenomas are classified by function as defined by clinical symptoms and signs of hormone hypersecretion with subsequent confirmation on immunohistochemical staining. However, positive immunostaining for pituitary cell types has been shown for clinically nonfunctioning adenomas, and this entity is classified as silent functioning adenoma. Most common in these subtypes include silent gonadotroph adenomas, silent corticotroph adenomas and silent somatotroph adenomas. Less commonly, silent prolactinomas and thyrotrophinomas are encountered. Appropriate classification of these adenomas may affect follow-up care after surgical resection. Some silent adenomas such as silent corticotroph adenomas follow a more aggressive course, necessitating closer surveillance. Furthermore, knowledge of the immunostaining characteristics of silent adenomas may determine postoperative medical therapy. This article reviews the incidence, clinical behavior, and pathologic features of clinically silent pituitary adenomas.

A patient with thyrotropinoma cosecreting growth hormone and follicle-stimulating hormone with low alpha-glycoprotein: a new subentity?

BACKGROUND

Thyrotropinomas are rare pituitary tumors. In 25 percent of cases there is autonomous secretion of a second pituitary hormone, adding to the clinical complexity. We report a patient with thyrotropin (TSH)-dependant hyperthyroidism along with growth hormone (GH) and follicle-stimulating hormone (FSH) hypersecretion but low alpha-glycoprotein (alpha-subunit) concentrations, a hitherto unique constellation of findings.

SUMMARY

A 67-year-old Scottish lady presented with longstanding ankle edema, paroxysmal atrial fibrillation, uncontrolled hypertension, fine tremors, warm peripheries, and agitation. Initial findings were a small goiter, elevated serum TSH of 7.37 mU/L (normal range, 0.30-6.0 mU/L), a free-thyroxine concentration of 34.9 pmol/L (normal range, 9.0-24.0 pmol/L), a flat TSH response to TSH-releasing hormone, and serum alpha-subunit of 3.1 IU/L (normal, <3.0 IU/L). There was no evidence of an abnormal thyroid hormone beta receptor by genotyping. Serum FSH was 56.8 U/L, but the luteinizing hormone (LH) was 23.6 U/L (postmenopausal FSH and LH reference ranges both >30 U/L) Basal insulin-like growth factor I was elevated to 487 microg/L with the concomitant serum GH being 14.1 mU/L, and subsequent serum GH values 30 minutes after 75 g oral glucose being 19.1 mU/L and 150 minutes later being 13.7 mU/L. An magnetic resonance imaging pituitary revealed a macroadenoma. Pituitary adenomectomy was performed with the histology confirming a pituitary adenoma, and the immunohistochemistry staining showed positive reactivity for FSH with scattered cells staining for GH and TSH. Staining for other anterior pituitary hormones was negative. After pituitary surgery she became clinically and biochemically euthyroid, the serum IFG-1 became normal, but the pattern of serum FSH and LH did not change.

CONCLUSION

This case of plurihormonal thyrotropinoma is unique in having hypersecretion of TSH, GH, and FSH with low alpha-subunit. Such a combination may represent a new subentity of TSHomas.

Medical management of thyrotropin-secreting pituitary adenomas

Thyrotropin-secreting pituitary tumors (TSH-omas) are a rare cause of hyperthyroidism and account for less than 1% of all pituitary adenomas. It is however noteworthy that the number of reported cases tripled in the last years as a consequence of the routine use of ultrasensitive immunometric assays for measuring TSH levels. Contrary to previous RIAs, ultrasensitive TSH assays allow a clear distinction between patients with suppressed and those with non-suppressed circulating TSH concentrations, i.e. between patients with primary hyperthyroidism (Graves' disease or toxic nodular goiter) and those with central hyperthyroidism (TSH-oma or pituitary resistance to thyroid hormone action). Failure to recognize the presence of a TSH-oma may result in dramatic consequences, such as improper thyroid ablation that may cause the pituitary tumor volume to further expand. The medical treatment of TSH-omas mainly rests on the administration of somatostatin analogs, such as octreotide and lanreotide. In fact, administration of dopamine agonists failed to persistently block TSH secretion in almost all patients and caused tumor shrinkage only in those with combined hypersecretion of TSH and PRL. On the contrary, somatostatin analogs were effective in reducing TSH and alpha-subunit secretion in more than 90% of cases with consequent normalization of FT4 and FT3 levels and restoration of the euthyroid state in the majority of them. In about one third of patients, a clear shrinkage of tumor mass and vision improvement could be demonstrated. Tachyphylaxis, cholelithiasis and carbohydrate intolerance occurred in a minority of treated patients. Whether somatostatin analog treatment may be an alternative to surgery and/or irradiation in patients with TSH-oma remains to be established. Nonetheless, the long-acting somatostatin preparations represent a useful tool for long-term treatment of such a rare pituitary tumors.

Plurihormonal pituitary adenomas: immunostaining of all pituitary hormones is mandatory for correct classification

AIMS

We studied the clinicopathological characteristics of plurihormonal pituitary adenomas.

METHODS AND RESULTS

The study material included 167 plurihormonal adenomas, which consisted of 31% of the surgically removed pituitary adenomas that we collected during a 12-year period. The mean age of patients with plurihormonal adenoma was 45.7 years (range 13-75 years). There were 86 men and 81 women. All tumours were fully classified by immunohistochemical staining for seven pituitary hormones or subunits. Thirty immunohistochemical subtypes of plurihormonal adenomas were recognized. Hormonal symptoms were present in 70% of patients, while serum hormonal levels were increased in 89% of patients. Most patients had symptoms related to only one of the hormones and only 7% of patients had symptoms related to two hormones. The most common hormonal symptom was acromegaly (50%); symptoms related to hyperprolactinaemia ranked second (20%). Double immunostaining of all the possible combinations of the hormones was performed in 30 selected tumours, and they all showed mixtures of hormones in individual adenoma cells in any hormonal combinations studied. The latter finding supported the view that plurihormonal adenomas are monomorphous adenomas.

CONCLUSIONS

Plurihormonal adenomas are common pituitary adenomas. Immunohistochemical staining of all pituitary hormones is mandatory for correct classification.

Pituitary lactotroph adenomas develop after prolonged lactotroph hyperplasia in dopamine D2 receptor-deficient mice

Tuberoinfundibular dopamine tonically inhibits PRL expression and secretion from the pituitary gland by the activation of dopamine D2 receptors (D2R) localized on lactotrophs. Mutant female mice that lack D2Rs have persistent hyperprolactinemia but also develop extensive hyperplasia of pituitary lactotrophs and peliosis of the adenohypophysis at 9 to 12 months of age, while age-matched male D2R-deficient mice have no morphologic adenohypophysial lesion. We now report that both female and male D2R-deficient mice 17 to 20 months of age develop pituitary lactotroph adenomas. Of 12 aged female mice examined, all developed monohormonal PRL-immunoreactive neoplasms that had a characteristic juxtanuclear Golgi pattern of PRL staining and loss of the reticulin fiber network. Several of these adenomas were 50-fold larger than normal glands with marked suprasellar extension and invasion of brain but no gross evidence of distant metastases. They also had striking peliosis that was more marked than the lesion seen in the hyperplastic pituitaries of the younger females. These findings demonstrate that a chronic loss of neurohormonal dopamine inhibition promotes the hyperplasia-neoplasia sequence in adenohypophysial lactotrophs. Our results are analogous to previous data indicating that protracted stimulation of adenohypophysial cells by hormones or growth factors results in proliferation with initial hyperplasia followed by the development of neoplasia. Six aged male D2R-deficient mice had slightly enlarged anterior pituitaries similar in size to normal female glands. However, each case exhibited multifocal, microscopic lactotroph adenomas with strong nuclear immunoreactivity for estrogen receptors and Pit-1 transcription factor. The unexpected development of adenomas in males without preexisting or concomitant hyperplasia suggests that prolonged loss of dopamine inhibition may also cause neoplasia by distinct cellular mechanisms in male and female animals.

Thyrotropin-secreting pituitary adenomas

Normal or elevated thyrotropin (TSH) levels in hyperthyroid patients are characteristic of rare TSH-secreting pituitary adenoma (TSH-oma), which is easily detectable by computed tomographic (CT) scan or magnetic resonance imaging (MRI). Other diagnostic aids are an absent/impaired TSH response to thyrotropin-releasing hormone (TRH), discrepant TSH and alpha-subunit responses to TRH, high sex hormone-binding globulin (SHBG) levels, high alpha-subunit levels, and a high alpha-subunit/TSH molar ratio. Familial studies help rule out thyroid hormone resistance (RTH). Surgical removal of TSH-oma leads to clinical and biochemical remission in most patients. In surgical failures, radiotherapy and octreotide treatment have a high success rate. Undetectable TSH 1 week postsurgery suggests a definitive cure, backed up by tests for cosecreted hormones from the adenoma and dynamic tests of TSH suppression.

Novel features of tumors that secrete both growth hormone and prolactin in acromegaly

The most prominent previously reported clinical features of growth hormone (GH) and prolactin (PRL)-secreting pituitary adenomas associated with acromegaly have included the high incidence of galactorrhea in women and a generally more favorable response to dopamine agonist therapy. The authors analyzed a consecutive series of 62 acromegalic patients treated with transsphenoidal microsurgery. GH-PRL tumors were found in 30% of the patients. There was a significant difference in sex distribution between acromegalics with the GH-PRL tumor subtype and all other acromegalics. Women represented 73% of the GH-PRL immunostain subtype, as compared with the overall sex distribution of 33 women (53%) and 29 men (47%) for the entire series of acromegalic patients. Individuals with the GH-PRL subtype had significantly higher postoperative GH levels than those with the GH subtype, and significantly higher postoperative GH levels when compared with all other acromegalics with a variety of immunostain subtypes. Linear regression analysis of the pre- and postoperative GH data revealed that the increased postoperative GH levels in the GH-PRL immunostain subtype were independent of the invasiveness of the tumor and of sex of the subject. When the same linear regression technique was used, lower preoperative levels of thyroxine and thyroid-stimulating hormone were observed in the GH-PRL subtype. These data suggest inherent differences characteristic of tumors that secrete both growth hormone and prolactin.

Cytokeratin distribution and functional properties of growth hormone-producing pituitary adenomas

In addition to its structural function, cytokeratin may have other important roles within cells. We have reported that in growth hormone-producing adenomas (GH cell adenomas), two distinct types can be recognized by their cytokeratin distribution patterns (dot-like or perinuclear pattern) and that each type has different clinicopathological and endocrinological properties. To confirm these phenomena in a larger series and to clarify the significance of different cytokeratin distribution patterns, we studied cytokeratin localization in 70 GH cell adenomas from acromegalic patients. Type I adenomas ( 15) almost exclusively (>98%) composed of cells with a prominent, dot-like distribution; type 2 adenomas (36) comprised of cells with perinuclear cytokeratin; and type 3 adenomas (11) comprised of both cell types were separated. The remaining 8 did not exhibit a distinct distribution pattern. By electron microscopic immunocytochemistry for cytokeratin, dot-like distribution corresponded to fibrous bodies, whereas perinuclear distribution represented immune deposition in the perinuclear zone. Immunohistochemistry for GH, prolactin, β-thyrotropin, and α-subunit of glycoprotein hormones revealed a reduced expression of these hormones in type 1 adenomas, compared with types 2 and 3 adenomas. In normal pituitary glands, almost all GH cells showed a perinuclear cytokeratin distribution, and only a few GH cells exhibited a dot-like pattern. These findings suggest that a dot-like cytokeratin distribution in GH cells may be pathological (a change from physiological perinuclear distribution) and that adenomas with such a distribution may reduce endocrine activities as a result of unknown factors.

Growth hormone-producing pituitary adenomas: correlations between clinical characteristics and morphology

In this study, we compared the clinical and endocrinological characteristics, neuroimaging findings, surgical outcome, and conventional histological findings (including immunohistochemistry) with the electron microscopic appearance of 31 growth hormone (GH)-producing adenomas. By electron microscopy, these 31 tumors were divided into 23 densely granulated somatotroph adenomas (DG adenomas) and 8 sparsely granulated somatotroph adenomas (SG adenomas). SG adenomas more frequently affected younger women, but no significant correlation was found between the adenoma type and the characteristic signs and symptoms of acromegaly, the incidence of diabetes mellitus or hypertension, or the basal serum GH and insulin-like growth factor I levels. A distinct response of GH to thyrotropin-releasing hormone, bromocriptine, or GH-releasing hormone was significantly more common in patients with DG adenomas than in those with SG adenomas, whereas the incidence of a response to gonadotropin-releasing hormone or oral glucose was not significantly different between the two groups. An analysis of neuroimaging findings and surgical results indicated that SG adenomas were more likely to be macroadenomas with suprasellar extension or invasive tumors and had a lower surgical cure rate. However, postoperative radiotherapy seemed to be similarly effective in both types of adenoma to prevent a tumor recurrence and to reduce postoperative GH basal level in serum. Light microscopy showed that DG adenomas were mainly acidophilic and were immunopositive not only for GH but also for prolactin (43%), the beta subunit of thyroid-stimulating hormone (26%), and the alpha subunit of glycoprotein hormone (87%), whereas SG adenomas were almost all chromophobic and only revealed immunopositivity for GH.(ABSTRACT TRUNCATED AT 250 WORDS)

Polymorphism of thyrotropin and alpha subunit in human pituitary adenomas

To understand better why patients with TSH-secreting pituitary tumors exhibit variable degree of hyperthyroidism, we analyzed the various isoforms of TSH and alpha-subunit secreted by 4 TSH-secreting adenomas in primary culture. All patients had macrodenomas clinically associated with hyperthyroidism with normal to elevated TSH plasma levels. The in vivo molar alpha/TSH ratio ranged from 18.4 to 3.8. The hormone material secreted over 4 to 48 h in culture was separated by gel isoelectrofocusing, eluted and estimated by immunoassays. The release of free alpha-subunit was noticeably different among adenomas. Three tumors were found to release an homogeneous and acidic (pI = 5.4-4.5) species totally unrelated to the alpha-subunit dissociated from intrapituitary TSH (5 isoforms, pI = 8.8-5.8) while another was more heterogeneous (pI = 8.8, 8.4, 7.6, 6.8, 5.8, 5.4-4.5). Tumoral TSH exhibited at least six detectable isoforms (pI = 8.6, 8.3-8.0, 7.5, 7.0, 6.5, 6.0) very similar to those present in a purified intrapituitary hormone preparation. While intrapituitary TSH was composed of 70% of alkaline (pI = 8.6-7.5), 25% of neutral (pI = 7.0-6.0) and 5% (pI = 5.8-4.5) of acidic forms, these species were found to be more evenly distributed in adenomatous secretion (43%/42%/15%). The TSH-secreting tumors thus appeared to relase preferentially neutral and acidic forms of TSH than alkaline components but for one tumor, this ratio could be modified by chronic incubation with TRH. When assayed for their capacity to stimulate 3H-thymidine incorporation in FRTL-5 cells, neutral TSH appeared definitely less potent than the alkaline and acidic isohormones. Altogether, these data show that pituitary adenomas synthesize normal forms of TSH but release them in variable amount in the medium. When circulating in the blood, the ratio between active and inactive isoforms of TSH may thus be responsible for the variable stimulation of the thyroid gland observed in the patients.

Hyperthyroidism due to inappropriate secretion of thyrotropin in 10 patients

PURPOSE

The syndrome of inappropriate thyroid-stimulating hormone (TSH) secretion, characterized by elevated serum free thyroxine and triiodothyronine levels in association with measurable serum TSH concentrations, remains an uncommon cause of hyperthyroidism that is being recognized with increasing frequency. The hyperthyroidism may be due to either neoplastic pituitary TSH secretion or selective pituitary resistance to thyroid hormone. In an effort to better understand this rare cause of hyperthyroidism, we undertook a retrospective analysis of our institution's experience with this condition.

PATIENTS

We reviewed our cumulative experience (10 patients) with hyperthyroidism due to the syndrome of inappropriate secretion of TSH.

RESULTS

Six patients were diagnosed with TSH-secreting pituitary adenomas and four were found to have selective pituitary resistance to thyroid hormone. One patient with tumor had a TSH-secreting pituitary adenoma in the setting of multiple endocrine neoplasia syndrome. In all patients with tumor, hyperthyroidism was successfully treated with transsphenoidal adenomectomy with or without pituitary radiotherapy. All four patients with pituitary resistance had thyroid ablation or resection prior to their correct diagnosis. Therefore, therapy for this group of patients involved thyroid hormone replacement and efforts to suppress TSH hypersecretion. All 10 patients have done well clinically, with follow-up ranging from 2 weeks to 13 years.

CONCLUSIONS

Adequate treatment exists for the two primary causes of TSH hypersecretion. TSH-secreting pituitary adenomas are treated with surgery and, if necessary, adjuvant pituitary radiotherapy. The results are generally good if the tumor is diagnosed and treated at an early stage. Primary therapy for hyperthyroidism due to selective pituitary resistance to thyroid hormone is aimed at suppression of pituitary TSH hypersecretion. The evaluation of any patient with hyperthyroidism must be thorough and, in some cases, should include measurement of TSH to determine the presence of inappropriate secretion. Eliminating this diagnosis will help avoid improper and potentially harmful treatment of hyperthyroid patients.

Expression of glycoprotein hormones and intracytoplasmic distribution of cytokeratin in growth hormone-producing pituitary adenomas

Sixteen growth hormone (GH)-producing pituitary adenomas were studied for the expression of glycoprotein hormone subunits and cytokeratin by light microscopic immunohistochemistry. Cytokeratin immunoreactivity was demonstrated in all adenomas, but its intracytoplasmic distribution showed two distinct patterns; a prominent, dot-like pattern and a diffuse, perinuclear pattern. Seven adenomas (type 1) were exclusively composed of cells with cytokeratin in a dot-like pattern, whereas 9 adenomas (type 2) comprised of cells with cytokeratin of perinuclear distribution. The expression of alpha-subunit of glycoprotein hormone was significantly different between the two types of adenomas; 8 of 9 adenomas of type 2 contained many alpha-subunit immunoreactive cells but none of type 1 adenomas showed any immunoreactivity. Only a small number of adenoma cells were positive for beta-subunit of thyrotropin stimulating hormone in 3 adenomas of type 2. beta-subunits of follicle stimulation hormone and luteinizing hormone were negative in all adenomas. These findings suggest that the expression of glycoprotein hormone subunits in GH-producing adenomas may be closely linked to their types distinguishable by the cytokeratin distribution pattern.