Hyperthyroidism due to selective pituitary resistance to thyroid hormones in a 15-month-old boy: efficacy of D-thyroxine therapy

A 15-month-old boy had clinical features of hyperthyroidism. In spite of elevated serum thyroid hormone levels (mean serum T4, 230 nmol/L; T3, 4.2 nmol/L), serum TSH levels ranged between 3.3-5.6 mU/L and rose to 35.4 mU/L after TRH stimulation. There was no abnormal serum thyroid hormone binding or any evidence of a pituitary tumor. The boy was treated with carbimazole for 6 months and became euthyroid. However, his thyroid size enlarged, and serum TSH rose to 45 mU/L. In an attempt to suppress TSH secretion, 3,5,3'-triiodothyroacetic acid was added to carbimazole in daily doses from 0.7-1.4 mg. This combined therapy failed to suppress TSH secretion (serum TSH, 10.2 mU/L) and led to recurrence of symptoms of hyperthyroidism. A trial using highly purified dextrothyroxine (contamination by L-T4, 0.05%) as sole therapy then was carried out. Serum TSH levels promptly declined to normal, both basally and after TRH stimulation (basal, 2.4 mU/L; peak, 13.8 mU/L). During a 24-month follow-up period, the boy remained euthyroid. Serum TSH levels remained in the normal range, as did his serum L-T4 levels (93 nmol/L). Complete remission was achieved using a 5-mg daily dose of D-T4. Temporary discontinuation of D-T4 led to prompt relapse of hyperthyroidism. Our patient's TSH hypersecretion appears to be due to selective pituitary resistance to thyroid hormones. Purified D-T4 effectively inhibited TSH secretion in this patient, without inducing significant side-effects, even when the daily dose was high. The cause of partial pituitary unresponsiveness to thyroid hormones is not known. We suggest that transport of thyroid hormones into the thyrotroph cells could be deficient in our patient.     

Anti-iodothyronine autoantibodies in a girl with hyperthyroidism due to pituitary resistance to thyroid hormones.

In the present study, we report the uncommon case of a 9.6-yr-old girl with circulating anti-T3 autoantibodies (T3-Ab) and hyperthyroidism due to inappropriate secretion of TSH (IST). The diagnosis of IST was based on the findings of normal TSH levels (2.4 mU/L) in the presence of high free T4 (28.2 pmol/L) and free T3 (FT3) levels, as measured by direct measurement methods based on "one-step" analog tracer (28.0 pmol/L) and "two-step" Lisophase (13.3 pmol/L) techniques. The discrepancy between the two measurements suggested a methodological interference due to T3-Ab in "one-step" technique, being the "two-step" methodology unaffected by the presence of such autoantibodies. T3-Ab were documented by high nonspecific binding of serum to labeled T3 (38.0% vs 4.3 +/- 2.1% in controls). The clinical picture of hyperthyroidism, the qualitatively normal TSH responses to TRH and T3 suppression tests, the normal pituitary imaging and the values of some parameters of peripheral thyroid hormone action compatible with hyperthyroidism indicated that the patient was affected by pituitary resistance to thyroid hormones (PRTH). Chronic treatment with dopaminergic agent bromocriptine (7.5 mg/day) did not cause TSH secretion to be suppressed, while the administration of thyroid hormone analog TRIAC (1.4 mg/day) inhibited TSH release (from 2.4 to 0.2 mU/L). As a consequence, circulating thyroid hormone levels normalized and euthyroidism was restored. During TRIAC administration, FT3 levels, measured by "one-step" analog tracer technique, gave spuriously high values due to the methodological interference of T3-Ab (15.2 vs 4.3 pmol/L as measured by "two-step" Lisophase technique).(ABSTRACT TRUNCATED AT 250 WORDS)     

Hyperthyroidism due to familial pituitary resistance to thyroid hormone: successful control with 3, 5, 3' triiodothyroacetic associated to propranolol.

We herein describe a family with thyroid hormone resistance. Thyroid hormones and basal TSH were elevated. Pituitary tumor or abnormality in thyroid hormone binding proteins were ruled out by appropriate tests. Mother and sister of the propositus presented similar abnormal hormonal features but no hyperthyroidism. Initially the patient was treated with carbimazole (30 mg/day): three months later a dramatic increase in the size of the thyroid gland and in TSH levels (12.5 to 28 mU/l) were noted. Thereafter, dextrothyroxine (D-T4) and 3, 5, 3'-triiodothyroacetic acid (TRIAC) were given consecutively and treatment was accompanied by a decrease of TSH levels (2 mU/l) but thyroid hormone remained elevated. The symptoms and signs of hyperthyroidism improved with the addition of propranolol (30-60 mg/day). In conclusion, the present report describes a new family with the syndrome of THR and variable degrees of involvement among relatives. We suggest the usefulness of TRIAC therapy to decrease TSH levels and propranolol to improve thyrotoxicosis due to pituitary resistance to thyroid hormone.     

Subtle primary hypothyroidism in patients treated for acute lymphoblastic leukemia

We evaluated serum thyroid hormone and thyroid antibody levels, the serum TSH response to TRH, and the circadian pattern of serum TSH in 10 children and adolescents after radiation therapy for acute lymphoblastic leukemia. Four patients had received central nervous system preventive cranial irradiation and intrathecal chemotherapy, and the remaining 6 patients were treated with craniospinal irradiation for central nervous system relapse. Serum total T4 and T3 concentrations were within the normal range and thyroid antibodies were negative in all patients. Four patients who had received craniospinal irradiation had low free T4 levels. Prior to TRH administration, the overall mean serum TSH concentration was 5.4 +/- 1.3 mU/l, and the mean peak response to TRH was 33 +/- 6.5 mU/l. Both were significantly increased when compared to the levels observed in our control population (p less than 0.05 and less than 0.025, respectively). The overall mean nadir diurnal TSH was 3.6 +/- 0.8 mU/l, and the mean peak nocturnal TSH was 6.9 +/- 1.3 mU/l, both significantly elevated when compared to normal children (p less than 0.025). The mean nocturnal TSH surge, however, was not significantly different from normal. Four of 6 children treated with craniospinal irradiation, and one of four children treated with cranial irradiation had increased basal and peak serum TSH concentrations in response to TRH. One of the patients treated with cranial irradiation had an abnormal nocturnal TSH surge. We conclude that subtle primary hypothyroidism is relatively common in patients with acute lymphoblastic leukemia, particularly in those who have been treated with craniospinal irradiation.     

Normal pituitary function and reserve after selective transsphenoidal removal of a thyrotropin-producing pituitary adenoma

A 37-yr-old woman with recurrent hyperthyroidism after partial thyroid ablation was found to have an enlarged sella turcica and elevated serum thyrotropin (TSH) and prolactin (PRL) levels measured by radioimmunoassay. Serum growth hormone (GH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), and cortisol levels were within normal limits and responded appropriately to provocative stimuli both before and after surgery. Preoperatively, the administration of thyrotropin-releasing hormone (TRH) (200 μg i.v.) and metoclopramide (MCP) (10 mg p.o.) induced a more than twofold increase in serum PRL levels, whereas TSH was only modestly affected. Bromocriptine (2.5 mg p.o.) and l-dopa (500 mg p.o.) suppressed TSH and PRL values to less than 50% of their initial values. After selective transsphenoidal removal of a pituitary adenoma, signs and symptoms of hyperthyroidism disappeared and TSH and PRL returned to normal. The postoperative administration of TRH and MCP produced a normal response for both PRL and TSH. Postoperatively, bromocriptine induced a parallel decrease in the serum level of both hormones, whereas l-dopa decreased PRL but had no effect on the serum TSH level. This case provides evidence that hyperthyroidism caused by a pituitary adenoma can be successfully treated by transsphenoidal surgery with preservation of normal pituitary function and reserve.     

Hyperthyroidism caused by a pituitary thyrotrophin-secreting tumour with excessive secretion of thyrotrophin-releasing hormone and subsequently followed by Graves' disease in a middle-aged woman

A 46-year-old woman had signs of thyrotoxicosis and galactorrhoea. Serum immunoreactive TSH and its alpha-subunit increased in the presence of high serum triiodothyronine (T3), thyroxine (T4), and free T4 concentrations, whereas beta-subunit TSH was undetectable. Exogenous TRH failed to increase serum TSH. Serum TSH was markedly suppressed by glucocorticoid, but was increased by antithyroid drug. L-Dopa or bromocriptine partially suppressed, but nomifensine had no influence on serum TSH. Serum prolactin (Prl) was above normal and markedly increased by TRH, but depressed by bromocriptine and not suppressed by nomifensine. Plasma TRH was normal in the hyperthyroid state, but was increased by glucocorticoid and antithyroid drug. Excess thyroid hormone depressed plasma TRH concentrations. Basal serum GH levels were constantly low. Transsphenoidal removal of the tumour normalized serum hormones (T3, T4 free T4, TSH, alpha-subunit and Prl), and eradicated the clinical signs of hyperthyroidism and galactorrhoea. Histological study of the tumour tissue demonstrated both thyrotrophes and somatotrophes. A reciprocal relationship between serum TSH and T4 concentrations shifted to a higher level before but was normalized after removal of the tumour. Ten months later, the clinical signs of thyrotoxicosis and the increase in serum thyroid hormone recurred without a concomitant increase in serum TSH and its alpha-subunit. Thyroidal auto-antibodies were slightly positive, but thyrotrophin-binding inhibitor immunoglobulin (TBII) was negative. Administration of antithyroid drug produced a euthyroid state, but 3 years later, discontinuation of the treatment resulted in recurrent hyperthyroidism without suppressed plasma TRH and with no evidence of regrowth of the pituitary tumour. It is suggested that the patient initially had hyperthyroidism owing to excessive TSH secretion from the tumour caused by abnormal TRH secretion, and subsequently had hyperthyroidism owing to Graves' disease.     

选择性垂体甲状腺激素抵抗所致TSH甲亢一例的治疗观察

本文报告１例选择性垂体对甲状腺激素抵抗所致ＴＳＨ甲亢。用ＰＴＵ治疗１３个月后，血清ＦＴ＿３、ＦＴ＿４水平持续高于正常，血清ＴＳＨ值波动于２６～６０ｍＵ／Ｌ之间，ＴＲＨ兴奋试验呈过度反应。改用溴隐亭治疗６个月后，血清基础ＴＳＨ及ＴＳＨ对ＴＲＨ反应均恢复正常，血清ＴＴ＿３、ＴＴ＿４水平也随之逐渐下降至正常，甲亢症状控制。Ｄ－Ｔ＿４治疗１１天，血清基础ＴＳＨ值保持正常，对ＴＲＨ无反应，而血清ＦＴ＿４、ＴＴ＿４水平回升至高于正常范围，甲亢复发。我们的观察说明，溴隐亭治疗这类甲亢有效，副作用小，可长期使用。     

Familial thyroid hormone resistance

Eight patients with thyroid hormone resistance were found in four generations of a kindred containing 19 members. Results of studies in this family are consistent with an autosomal dominant mode of inheritance for this disorder. The affected family members were clinically euthyroid but all had goiters and markedly increased serum thyroid hormone levels: thyroxine (T4) = 21.1 +/- 2.1 microgram/dl; triiodothyronine (T3) = 323 +/- 60 ng/dl; free T4 = 5.4 +/- 0.9 ng/dl; and free T3 = 1,134 +/- 356 pg/dl (mean +/- SD). Serum thyrotropin (TSH) levels were normal or slightly elevated in six patients and responded normally to the administration of thyrotropin-releasing hormone (TRH) and L-triiodothyronine. Two patients who had previously undergone subtotal thyroidectomy had elevated baseline serum TSH levels and exaggerated TSH responses to the administration of TRH suggesting subclinical hypothyroidism despite elevated total and free thyroid hormone levels. The absence of thyrotoxicosis and normal serum TSH levels despite elevated serum free T3 and T4 levels in the untreated members of this family are consistent with resistance of pituitary and peripheral tissues to the actions of thyroid hormones. In addition, the absence of hypothyroidism and normal responsiveness of serum TSH to TRH and L-triiodothyronine administration in untreated family members suggest that the thyroid has compensated for the hormone resistance by increased secretory activity under the control of pituitary TSH secretion.     

Peripheral resistance to thyroid hormone in an infant

Peripheral resistance to thyroid hormone, a syndrome characterized by elevated serum total and free thyroid hormone levels and abnormal TSH suppression without manifestations of hyperthyroidism, was studied in a clinically euthyroid 6-month-old infant. Initial serum concentrations of T4, T3, and TSH were 22.1 micrograms/dl, 334 ng/dl, and 7.6 microunits/ml, respectively; infusion of synthetic TRH increased the serum TSH to 47.4 microunits/ml, an exaggerated response. Pituitary insensitivity to T3 was investigated by measuring these parameters in response to consecutive 7-day courses of increasing doses of T3. Four times the calculated replacement dose of T3 (40 micrograms/day) was required to normalize the serum T4 and the serum TSH response to TRH. After administration of 80 micrograms/day T3, the serum TSH response to TRH was virtually abolished, but no clinical signs of thyroid hormone excess were observed. High doses of T4 blunted the serum TSH response to TRH in a manner similar to T3. Prednisone also decreased the TSH response to TRH but had no effect on serum thyroid hormone concentrations. In an attempt to determine the mechanism of thyroid hormone resistance, specific nuclear T3 binding was compared in cultured skin fibroblasts from the patient and a normal infant. Normal fibroblast nuclei had a single binding site with a Ka of 3.1 X 10(9) M-1. In contrast, the Scatchard plot of the patient's T3 binding was curvilinear, compatible with a high affinity site that had a Ka (4.2 X 10(9) M-1) similar to that of the normal fibroblasts and a second low affinity site (Ka = 2.7 X 10(8) M-1). Supraphysiological concentrations of T3 elicited a dose-related increase in fibroblast glucose consumption, which was similar in cells from both the patient and from a normal infant. In conclusion, pituitary and peripheral resistance to thyroid hormone has been demonstrated in this infant, but despite the abnormality of nuclear T3 binding, the cellular mechanisms remain unclear.     

A TSH secreting pituitary tumour causing hyperthyroidism: presentation of a case and review of the literature.

A 45 year old male with a 12 year history of mild hyperthyroidism and a pituitary tumour is presented. He had both clinical and laboratory evidence of hyperthyroidism and his serum TSH was persistently and markedly elevated. A TRH test resulted in no further rise in serum TSH. No evidence of pituitary or peripheral endocrine deficiencies existed and prolactin levels were normal. Craniotomy was performed and a pituitary adenoma was removed. On light microscopy, it was mostly composed of chromophobes. However, occasional granulated cells were observed, and on electron microscopy, most of the cells contained fine granules, which suggested possible thyrotroph origin of the tumour. One week post-operatively the patient's serum TSH returned to normal. Again, TRH produced no response in TSH. The patient became hypothyroid by clinical and laboratory findings and is currently on thyroid replacement therapy. The previously reported TSH secreting tumours associated with hyperthyroidism are reviewed.     

INAPPROPRIATE THYROTROPHIN SECRETION, INCREASED DOPAMINERGIC TONE AND PRESERVATION OF THE DIURNAL RHYTHM IN SERUM TSH

A patient presented with mild hyperthyroidism, elevated serum T4 and T3, and an inappropriately raised serum thyrotrophin (TSH). There was no evidence of pituitary tumour (alpha-subunit secretion and CT scan of the pituitary were normal). The TSH response to TRH was greater than normal. The elevated TSH was suppressed by oral triiodothyronine (100 micrograms daily for 10 d). The normal diurnal variation of TSH was preserved. Intravenous injection of the dopamine receptor blocking agent domperidone led to a greater than normal elevation in TSH (maximum increments 18-20 mU/l). This increased dopaminergic tone was similar in studies carried out in the morning and late evening. The dopamine agonist bromocriptine (2.5 mg twice daily) failed to suppress serum TSH either acutely or over 6 weeks. The circadian rhythm was unaltered by this treatment. Basal serum prolactin levels were normal, and responded appropriately to TRH, domperidone and bromocriptine. These observations indicate that dopamine does not control the diurnal variation of TSH in nontumoral TSH-mediated hyperthyroidism. The increased dopaminergic tone demonstrated may be secondary to the primary failure of pituitary-thyroid feedback in the condition.     

TSH secretion in Cushing's syndrome: relation to glucocorticoid excess, diabetes, goitre, and the 'sick euthyroid syndrome'

Thyrotrophin (TSH) secretion was studied in 63 patients with Cushing's syndrome (53 patients with pituitary dependent Cushing's disease, eight with adrenocortical tumours, and two with the ectopic ACTH syndrome). Prior to treatment, TSH response to 200 micrograms of TRH intravenously was significantly decreased compared to controls; TSH response was 'flat' (increment less than 2 mU/l) in 34 patients (54%). Patients with a flat response to TRH had significantly higher morning and midnight cortisol levels than patients with a TSH response of 2 mU/l and more; this was not due to differences in serum thyroid hormone levels. Basal TSH, TSH increment after TRH, and stimulated TSH value, but not serum triiodothyronine, were correlated with cortisol measurements (0800 h serum cortisol, midnight cortisol, and urinary free corticoid excretion). After exclusion of 40 patients with additional disease (severe systemic disease, diabetes mellitus, or goitre), cortisol-TSH correlations were even more pronounced (r = -0.73 for midnight cortisol and stimulated TSH levels), while in the patients with additional complications, these correlations were slight or absent. Successful treatment in 20 patients was associated with a rise in thyroid hormone levels and the TSH response to TRH. These results indicate that (1) the corticoid excess but not serum T3 is the principal factor regulating TSH secretion in Cushing's syndrome, (2) a totally flat response to TRH is rare, and (3) TSH suppression and lower than normal serum thyroid hormone levels are reversible after treatment. Since factors like severe systemic disease, diabetes mellitus and goitre also affect TSH secretion, they tend to obscure the statistically significant correlations between cortisol excess and TSH secretion.     

CLINICAL USEFULNESS OF A HIGHLY SENSITIVE ENZYME-IMMUNOASSAY OF TSH

Using a recently developed sensitive enzyme immunoassay (EIA) for TSH, serum TSH levels in normal subjects and patients with various thyroid disorders were measured. The minimum detectable concentration was less than 0.005 mU/l. An excellent correlation was observed between TSH values measured by EIA and by sensitive radioimmunoassay (r = 0.932). In 26 normal subjects, serum TSH ranged from 0.30 to 2.65 mU/l (geometric mean 0.97 mU/l). In 27 untreated hyperthyroid Graves' patients, serum TSH was detected in all but one, ranging from 0.005 to 0.19 mU/l (geometric mean 0.040). These values were proved to be specific for human TSH by absorption, recovery, cross-reactivity and dilution studies; non-specific serum effects were also ruled out. In 10 patients with destructive thyroiditis, similar TSH values (0.005-0.20 mU/l, mean 0.032) were observed. However, no significant correlations between TSH and circulating thyroid hormone levels were observed in these thyrotoxic conditions. Furthermore, 9 untreated Graves' patients did not respond to a single i.v. injection of TRH. In 13 hypothyroid patients with hypothalamo-pituitary disorders, 10 had basal TSH levels of less than 0.4 mU/l, and TRH tests in five gave peak TSH values of more than 0.8 mU/l, which were associated with significant increases in serum T3. In three patients with Sheehan's syndrome, elevated basal TSH levels were observed. Two of them responded to TRH, but these TSH elevations were not associated with T3 increases. In conclusion, this sensitive EIA could measure TSH levels in most patients with thyrotoxicosis and central hypothyroidism. However, the true significance of these measured values needs to be elucidated by future studies.     

Serum thyrotropin and prolactin in the syndrome of generalized resistance to thyroid hormone: responses to thyrotropin-releasing hormone stimulation and short term triiodothyronine suppression

Serum TSH and PRL levels and their response to TRH were measured in 11 patients with generalized resistance to thyroid hormone (GRTH), 6 euthyroid subjects, and 6 patients with primary hypothyroidism. TSH and PRL levels and their response to TRH were also measured after the consecutive administration of 50, 100, and 200 micrograms T3 daily, each for a period of 3 days. Using a sensitive TSH assay, all GRTH patients had TSH values that were elevated or within the normal range. On the basis of a normal or elevated TSH level, GRTH patients were classified as GRTH-N1 TSH (5 patients) or GRTH-Hi TSH (6 patients), respectively. Only GRTH patients with previous thyroid ablative therapy had basal TSH values greater than 20 mU/L. TSH responses, in terms of percent increment above baseline, were appropriate for the basal TSH level in all subjects. No GRTH patient had an elevated basal PRL level. PRL responses to TRH were significantly increased only in the hypothyroid controls compared to values in all other groups. On 50 micrograms T3, 7 of 12 (58%) nonresistant (euthyroid and hypothyroid) and 1 of 11 (9%) resistant subjects had a greater than 75% suppression of the TSH response to TRH. On the same T3 dose, 2 of 12 (17%) nonresistant and 4 of 11 (36%) resistant subjects had a greater than 50% suppression of the PRL response to TRH. On 200 micrograms T3, all subjects, except for 1 with GRTH, had a greater than 75% suppression of the TSH response to TRH. On the same T3 dose, while 11 of 12 (92%) nonresistant subjects had a greater than 50% reduction of the PRL response to TRH, only 3 of 10 (30%) resistant patients showed this degree of suppression (P less than 0.005). Without previous ablative therapy, serum TSH in patients with GRTH is usually normal or mildly elevated. The TSH response to TRH is proportional to the basal TSH level and is suppressed by exogenous T3. However, on 200 micrograms T3 basal TSH was not detectable (less than 0.1 mU/L) in all euthyroid subjects, but it was measurable in three of four GRTH patients with normal TSH levels before T3 treatment. PRL levels in GRTH are normal even when TSH is elevated. The PRL response to TRH is not increased in GRTH. In all subjects, exogenous T3 suppresses the PRL response to TRH to a lesser degree than the TSH response, but this difference is much greater in patients with GRTH.     

Prenatal diagnosis of thyroid hormone resistance

A 29-yr-old woman with pituitary resistance to thyroid hormones (PRTH) was found to harbor a novel point mutation (T337A) on exon 9 of the thyroid hormone receptor beta (TRbeta) gene. She presented with symptoms and signs of hyperthyroidism and was successfully treated with 3,5,3'-triiodothyroacetic acid (TRIAC) until the onset of pregnancy. This therapy was then discontinued in order to prevent TRIAC, a compound that crosses the placental barrier, from exerting adverse effects on normal fetal development. However, as the patient showed a recurrence of thyrotoxic features after TRIAC withdrawal, we sought to verify, by means of genetic analysis and hormone measurements, whether the fetus was also affected by RTH, in order to rapidly reinstitute TRIAC therapy, which could potentially be beneficial to both the mother and fetus. At 17 weeks gestation, fetal DNA was extracted from chorionic villi and was used as a template for PCR and restriction analysis together with direct sequencing of the TRbeta gene. The results indicated that the fetus was also heterozygous for the T337A mutation. Accordingly, TRIAC treatment at a dose of 2.1 mg/day was restarted at 20 weeks gestation. The mother rapidly became euthyroid, and the fetus grew normally up to 24 weeks gestation. At 29 weeks gestation mild growth retardation and fetal goiter were observed, prompting cordocentesis. Circulating fetal TSH was very high (287 mU/L) with a markedly reduced TSH bioactivity (B/I: 1.1 +/- 0.4 vs 12.7 +/- 1.2), while fetal FT4 concentrations were normal (8.7 pmol/L; normal values in age-matched fetuses: 5-22 pmol/L). Fetal FT3 levels were raised (7.1 pmol/L; normal values in age-matched fetuses: <4 pmol/L), as a consequence of 100% cross-reactivity of TRIAC in the FT3 assay method. To reduce the extremely high circulating TSH levels and fetal goiter, the dose of TRIAC was increased to 3.5 mg/day. To monitor the possible intrauterine hypothyroidism, another cordocentesis was performed at 33 weeks gestation, showing that TSH levels were reduced by 50% (from 287 to 144 mU/L). Furthermore, a simultaneous ultrasound examination revealed a clear reduction in fetal goiter. After this latter cordocentesis, acute complications occured, prompting delivery by cesarean section. The female neonate was critically ill, with multiple-organ failure and respiratory distress syndrome. In addition, a small goiter and biochemical features ofhypothyroidism were noted transiently and probably related to the prematurity of the infant. At present, the baby is clinically euthyroid, without goiter, and only exhibits biochemical features of RTH. In summary, although further fetal studies in cases of RTH are necessary to determine whether elevated TSH levels with a markedly reduced bioactivity are a common finding, our data suggest transient biochemical hypothyroidism in RTH during fetal development. Furthermore, we advocate prenatal diagnosis of RTH and adequate treatment of the disease in case of maternal hyperthyroidism, to avoid fetal thyrotrope hyperplasia, reduce fetal goiter, and maintain maternal euthyroidism during pregnancy.     

Thyrotropin-secreting pituitary adenomas: report of seven cases.

Seven patients with hyperthyroidism due to a TSH-secreting pituitary macroadenoma have been observed of a total of 800 patients with pituitary tumors over a period of 15 yr. Serum TSH levels varied between 1.1-36.3 mU/L. The serum alpha-subunit level was low in 1 case, while in 4 other cases the concentration was elevated and varied between 3.7-7.8 micrograms/L. Serum TSH beta levels were normal in the 4 cases in which it was determined. Serum GH or PRL levels were elevated in 5 cases. In 1 patient the cosecretion of TSH, GH, and PRL was confirmed by immunocytochemical examination. Serum TSH and alpha-subunit responses to TRH, GnRH, CRF, GRF, dexamethasone, methimazole, T3, and bromocriptine administration were variable when studied. Serum TSH and alpha-subunit circadian rhythms were absent in 1 case and inverted in another. A serum alpha-subunit pulsatility without TSH pulses was observed in 1 patient. Five patients underwent transsphenoidal adenomectomy. Three of 4 patients operated on in our center were cured, but a recurrence of the adenoma was found in 1 of them after 5 yr. The fifth patient was not cured. Treatment with octreotide in 3 patients resulted in normalization of serum TSH, GH, and thyroid hormones levels. Cosecretion of PRL in 1 case and alpha-subunit in 2 cases was also inhibited. Partial tachyphylaxis occurred in 1 patient. In summary, heterogeneity in clinical presentation, hormonal expression, and therapeutic response appears to characterize these TSH-secreting adenomas.     

Syndrome of 'inappropriate secretion of thyroid-stimulating hormone' by partial target organ resistance to thyroid hormones

A 74 year old woman was found to have elevated serum thyroid-stimulating hormone (TSH) levels and elevated serum thyroid hormone levels, with clinical euthyroidism. There was no evidence of a pituitary tumor. TSH levels increased substantially during methimazole therapy. Administration of dexamethasone was followed by a prompt fall in serum TSH levels. Triiodothyronine (T3) was administered over a period of 20 days in doses from 25 micrograms to as much as 100 micrograms daily causing a rise in serum T3 above 700 ng/100 ml, a decline of T4 and a blunting of the response to thyrotrophin-releasing hormone (TRH), with normal metabolic responses (pulse rate, photomotogram, cholesterol). These results suggest that the patient's disorder is due to partial target organ resistance to thyroid hormones.     

3,5,3'-triiodothyroacetic acid therapy for thyroid hormone resistance

3,5,3'-Triiodothyroacetic Acid (Triac) is reputed to suppress pituitary secretion of TSH with minimal metabolic effects. Triac has been used successfully to treat eight patients with thyroid hormone resistance. We gave Triac to a woman with selective pituitary resistance for treatment of hyperthyroidism (patient 1) and to a man with generalized resistance and chronic schizophrenia to determine whether it would improve his schizophrenia (patient 2). Patient 1 was given 0.35-3.5 mg Triac/day; patient 2 was given 0.7-4.2 mg/day. Dosages were increased by 0.7 mg/day every 2 weeks. Serum T3, T4, free T4, TSH, TSH response to TRH, systolic time intervals (STI), angiotensin-converting enzyme (ACE), and lipids were monitored bimonthly. In both patients, there was no change in symptoms, weight, lipids, or STI. In patient 1, basal TSH suppressed from 16.3 to 1.5 mU/L; in patient 2, from 2.0 to 0.5 mU/L. The peak TSH response to TRH stimulation decreased from 144 to 12.5 mU/L in patient 1 and from 14.2 to 2.8 mU/L in patient 2. Serum T4 decreased from 160 to 109 nmol/L in patient 1 and from 270 to 192 nmol/L in patient 2. ACE levels were persistently elevated in both patients. Resting energy expenditure, measured by oxygen consumption, was increased by Triac in both patients (12% in patient 1 and 9% in patient 2). Although Triac suppressed TSH and T4 secretion in both patients, it did not reduce peripheral action of thyroid hormone as expressed in STI, resting energy expenditure, and ACE. We conclude that in these two patients with resistance to thyroid hormone, at the doses used to suppress TSH and T4 secretion, the intrinsic peripheral action of Triac offset whatever decrease in thyroid hormone secretion it produced.     

Hyperthyroidism due to a TSH-secreting pituitary tumor

A 28-year-old female with a 12-year history of goiter is presented. She had both clinical and laboratory evidence of hyperthyroidism, and her serum TSH was persistently and markedly elevated after treatment with antithyroid drugs. A TRH stimulation test resulted in no further rise in serum TSH after cessation of medication. Menses were regular and serum prolactin levels were normal. Serum LH and FSH responses to LHRH stimulation test were normal. No other evidence of pituitary or peripheral endocrine deficiencies existed. She underwent a subtotal thyroidectomy followed by 131I therapy three years later. A pituitary adenoma with sphenoidal and suprasellar extension was completely removed by transphenoidal approach. On light microscopy, it was mostly composed of chromophobic cells with occasional calcification showing sinusoidal pattern. On electron microscopy, most of the cells contained fine granules, which suggested thyrotroph. The immunoperoxidase technique revealed TSH beta in the cytoplasm of some adenoma cells. Three days postoperatively the patient's serum TSH levels returned to normal. TRH stimulation test produced a normal response in serum TSH. The patient was diagnosed hypothyroid by laboratory findings and is currently on thyroid replacement therapy. The patient became pregnant and delivered twice prior to the operation for pituitary adenoma. The previously reported TSH secreting adenomas associated with hyperthyroidism were reviewed.