Familial hyperthyroidism due to inappropriate thyrotropin secretion successfully treated with triiodothyronine

[Therapeutic possibilities in patients with selective pituitary resistance to thyroid hormones]

Selective pituitary resistance to thyroid hormones (SPRTH) is a non-neoplastic form of inappropriate secretion of thyrotropin (TSH). The etiology of this hormonal resistance is linked to inactivating mutations in the thyroid hormone receptor beta (TR-beta) gene. These mutations affect critical portions of the receptor's triiodothyronine (T3)-binding domain. Clinically, SPRTH is characterized by hyperthyroidism with goiter and absence of pituitary mass in the morphologic study. Laboratory data show an elevation of free T3 and free thyroxine concentrations without suppression of TSH, with normal molar subunit alpha/TSH ratio. At this time, there is no specific therapy for SPRHT. Beta blockers, such as atenolol, and benzodiazepines have been used as a symptomatic therapy. Among the drugs with the capacity for reducing TSH secretion are TR agonists, such as triiodothyroacetic acid, D-thyroxine, triiodothyropropionic acid, and L-T3.

Subclinical hypothyroidism in infertile women: the importance of continuous monitoring and the role of the thyrotropin-releasing hormone stimulation test

The aim of our study was to assess the prevalence of subclinical hypothyroidism (SH) after administering a thyrotropin-releasing hormone (TRH) stimulation test among women with normal serum thyroid-stimulating hormone (TSH) levels and various causes of infertility. Eighty-seven infertile women (39 with ovulation disorders and 48 with other causes of infertility) had a TRH stimulation test on day 3 - 7 of their cycle. Exaggerated TSH response (>30 mIU/l at 20, 40 or 60 min) following intravenous injection of 400 microg TRH was defined as SH. The TRH test was performed 2 - 4 months after the first visit to the clinic. We found that the prevalence of SH was significantly higher among women with ovulation disorders (20.5%) than among women with normal ovulation (8.3%). In addition, we found that although basal TSH levels were normal at recruitment, 2 - 4 months later these levels were abnormally high in 8% of the women. All these women had an abnormal TRH test. We recommend performing TRH stimulation testing in women suffering from ovulation disorders who have normal basal TSH levels, followed by repeat assessments of thyroid function to enable treatment with thyroxine in cases with abnormal results.

Generalized resistance to thyroid hormone associated with possible selective cardiac nonresistance

OBJECTIVE

To review the condition of generalized resistance to thyroid hormone and to report a case of generalized thyroid hormone resistance associated with atrial fibrillation.

METHODS

A case report is presented of a 52-year-old man with atrial fibrillation who was referred by a cardiologist for thyroid ablation because of "hyperthyroidism," when his free thyroxine was found to be 4.35 ng/dL (normal, 0.55 to 2.46) and his free triiodothyronine was 6.5 pg/mL (normal, 1.4 to 4.4).

RESULTS

This clinically euthyroid man with no signs or symptoms of hyperthyroidism except for the possibly related atrial fibrillation had a thyrotropin level of 3.45 mIU/L (normal, 0.46 to 4.7) in conjunction with the aforementioned increased levels of thyroid hormones. Further evaluation revealed normal 6-hour (11.7%) and 24-hour (27.6%) (123)I uptakes. Magnetic resonance imaging of the pituitary revealed a normal-sized gland with no masses.

CONCLUSION

This is a rare case of generalized resistance to thyroid hormone in a patient with only atrial fibrillation. Whether the heart was selectively nonresistant to thyroid hormone as the cause of his atrial fibrillation or whether his atrial fibrillation was due to his mitral valve prolapse documented on echocardiography could not be determined with certainty. His ventricular rate of 83 per minute and laboratory evaluation suggest that thyroid hormone was not the cause of the atrial fibrillation.

Resistance to thyroid hormone and its molecular basis

Generalized resistance to thyroid hormone (GRTH) is an inherited syndrome characterized by hyposensitivity of target tissues to thyroid hormone. The clinical presentation is variable. The syndrome is usually suspected when elevated serum thyroid hormone levels are associated with a non-suppressed thyroid-stimulating hormone (TSH). While goiter and thyroid test abnormalities have more often led to the suspicion of thyroid gland dysfunction, short stature, hyperactivity, learning disability and goiter in children or adolescents and recalcitrant goiter in adults, should raise the suspicion of GRTH. Hypothyroidism has been considered when growth or mental retardation was the presenting symptom and thyrotoxicosis when confronted with attention deficit, hyperactivity or tachycardia. Failure to recognize the inappropriate persistence of TSH secretion in spite of elevated thyroid hormone levels has commonly resulted in erroneous diagnosis leading to antithyroid treatment. More than 300 subjects with this syndrome have been identified. The mode of inheritance in the majority of families is autosomal dominant. Recessive transmission has been found in only one family. It has long been speculated that this defect is likely to be caused by an abnormal thyroid hormone receptor (TR), but this hypothesis could not be directly tested until the isolation of two TR genes, TR alpha and TR beta. Mutations in the TR beta gene have been identified in 42 families with GRTH. All are located in the T3-binding domain straddling the putative dimerization region and exhibit various degrees of hormone-binding impairment. This finding, and the fact that heterozygous subjects with complete TR deletion are not affected while those with point mutations are, indicates that interactions of a mutant TR with normal TR and with other factors are responsible for the dominant inheritance of GRTH and its heterogeneity. Elucidation of the etiology of GRTH has not only added a new means for the early diagnosis of the syndrome but provided new insights in the understanding of the mechanism of hormone action.

Thyroid hormone resistance syndromes

The thyroid hormone resistance syndromes are disorders in which the body's tissues are resistant to the effects of thyroid hormone. Generalized resistance to thyroid hormone (GRTH) is characterized by resistance in the pituitary gland and in most or all of the peripheral tissues. Affected individuals have elevated serum thyroid hormone levels and inappropriately normal or elevated thyroid-stimulating hormone (TSH) but are usually clinically euthyroid and require no treatment. Selective pituitary resistance to thyroid hormone (PRTH) is characterized by resistance in the pituitary gland but not in peripheral tissues. Patients have elevated serum thyroid hormone levels and normal or elevated TSH levels and are clinically thyrotoxic. Therapy is usually necessary, but current choices are not completely satisfactory. Selective peripheral resistance to thyroid hormone (PerRTH) is characterized by resistance in peripheral tissues but not in the pituitary. The only patient thus far described had normal serum thyroid hormone and TSH levels but was clinically hypothyroid and improved with thyroid hormone administration. All of these disorders are probably more common than is generally recognized and are often misdiagnosed and inappropriately treated. GRTH, in most cases studied, results from a mutation in the thyroid hormone receptor beta gene causing an amino acid substitution in or a partial or complete deletion of the thyroid hormone-binding domain of the receptor. The causes of PRTH and PerRTH remain to be determined.

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 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.

Dextrothyroxine in the treatment of generalized thyroid hormone resistance in a boy homozygous for a defect in the T3 receptor

The dextroisomer of thyroxine (D-T4) has been shown to have suppressive effects on pituitary TSH secretion in euthyroid individuals and patients with mild thyroid hormone resistance. We treated a 3-year-old boy with D-T4 who was homozygous for a T3 receptor defect, resulting in a complex clinical picture of tissue-specific hyperthyroidism and hypothyroidism. There was no evidence of significant alteration in thyroid physiology, including serum concentrations of basal and TRH stimulated TSH or echocardiographic parameters measuring systolic time interval. We conclude that D-T4 at a daily dose of 6 mg (0.65 mg/kg) was ineffective in this boy with homozygous dominant negative thyroid hormone resistance.

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.

Molecular diagnosis and characterization of thyroid hormone resistance syndromes

The genetic basis of generalized resistance to thyroid hormones (GRTH) is now well understood. In the majority of patients, diverse mutations in the T3-binding domain of the c-erbA beta thyroid hormone receptor gene result in variable clinical presentations. These mutations are dominant negative in that the mutant receptors inhibit the function of normal beta-receptor (from one allele) and normal alpha-receptor (from two alleles). Several mutant c-erbA beta receptors have been cloned and synthesized in vitro; these receptors display a wide range of T3-binding affinities from only a two-fold reduction to no detectable T3-binding activity. Recent transfection studies with T3-regulated reporter genes and these mutant receptors have confirmed the dominant negative function of the mutations in patients with GRTH. Two unique patients, the Refetoff and Bercu patients, display the clinical (phenotypic) results of total absence of beta-receptor and homozygous expression of a dominant negative mutant beta-receptor, respectively. Further clinical and molecular studies of GRTH should lead to greater insights of the nature of thyroid hormone action in man.

Clinical hyperthyroidism due to non-neoplastic inappropriate thyrotrophin secretion

We report a case of hyperthyroidism due to inappropriate thyrotrophin (TSH) secretion in a patient with selective pituitary resistance to thyroid hormone action. Symptoms of hyperthyroidism in patients with this disorder are usually mild, implying some peripheral tissue resistance to the metabolic effects of thyroid hormone. Our patient had unusually severe symptoms, including marked weight loss and cardiac arrythmias which required carbimazole and beta-blocker therapy for control. Somatostatin was ineffective in suppressing TSH secretion. The introduction of sensitive thyrotrophin assays should facilitate the accurate diagnosis of TSH-induced hyperthyroidism and avoid inappropriate treatment.

Thyrotoxicosis due to pituitary resistance to thyroid hormones. Successful control with D thyroxine: a study in three patients

Selective pituitary resistance to thyroid hormone (PRTH) is responsible for thyrotoxicosis due to inappropriate secretion of TSH. The TSH suppressive action of D-thyroxine (DT4) has been previously documented in euthyroid and hypothyroid subjects. This prompted us to treat with DT4 three patients with PRTH uncontrolled by anti-thyroid drugs (ATD) alone or supplemented with bromocriptine, and whose follow-up had been complicated by atrial fibrillation in two patients. Because of 100% cross-reactivity between the D and L isomers of T4 and T3 in our RIAs, thyroglobulin (Tg) was used as an index of thyroid secretion. Under ATD, TSH and Tg levels were respectively: 35 mIU/l and 670.5 pmol/l (patient 1), 87 mIU/l and 453 pmol/l (patient 2) and 110 mIU/l and 906 pmol/l (patient 3). When DT4 was added (patient 1, 3 mg daily; patients 2 and 3, 2 mg daily) to the same dose of ATD, plasma TSH and Tg levels fell but were still over the upper limit of normal and thyrotoxicosis persisted as illustrated by a recurrence of atrial fibrillation in one patient. When ATD were withdrawn and DT4 given alone (2 mg daily) all symptoms subsided within 1 month while TSH and Tg levels fell within the normal range. TSH normalization was documented within 1 week in one patient.(ABSTRACT TRUNCATED AT 250 WORDS)

A base mutation of the C-erbA beta thyroid hormone receptor in a kindred with generalized thyroid hormone resistance. Molecular heterogeneity in two other kindreds

Generalized thyroid hormone resistance (GTHR) is a disorder of thyroid hormone action that we have previously shown to be tightly linked to one of the two thyroid hormone receptor genes, c-erbA beta, in a single kindred, A. We now show that in two other kindreds, B and D, with differing phenotypes, there is also linkage between c-erbA beta and GTHR. The combined maximum logarithm of the odds score for all three kindreds at a recombination fraction of 0 was 5.77. In vivo studies had shown a triiodothyronine (T3)-binding affinity abnormality in nuclear receptors of kindred A, and we therefore investigated the defect in c-erbA beta in this kindred by sequencing a major portion of the T3-binding domain in the 3'-region of fibroblast c-erbA beta cDNA and leukocyte c-erbA beta genomic DNA. A base substitution, cytosine to adenine, was found at cDNA position 1643 which altered the proline codon at position 448 to a histidine. By allelic-specific hybridization, this base substitution was found in only one allele of seven affected members, and not found in 10 unaffected members of kindred A, as expected for a dominant disease. Also, this altered base was not found in kindreds B or D, or in 92 random c-erbA beta alleles. These results and the fact that the mutation is predicted to alter the secondary structure of the crucial T3-binding domain of the c-erbA beta receptor suggest this mutation is an excellent candidate for the genetic cause of GTHR in kindred A. Different mutations in the c-erbA beta gene are likely responsible for the variant phenotypes of thyroid hormone resistance in kindreds B and D.

Congenital hypothyroidism and partial thyroid hormone unresponsiveness of the pituitary in a patient with congenital thyroxine binding albumin elevation

We describe a girl who presented at the age of 6 weeks with cardiogenic shock due to congenital hypothyroidism (serum thyroxine (T4) less than 12 nmol/l). Thyroxine replacement therapy was instituted. In spite of high total serum T4 levels, thyroid stimulating hormone (TSH) serum values remained elevated. The raised serum T4 levels were the result of congenital elevation of thyroid binding albumin (TBA). Toxic doses of both T4 and triiodothyronine (T3) normalized the elevated TSH levels indicating that the pituitary is responsive to thyroid hormone, albeit at a higher threshold. In patients with congenital TBA elevation and an altered T4 pituitary response requiring thyroid replacement therapy, the measurement of serum free T4 levels is the parameter of choice to monitor treatment.

Pituitary-thyroid relationships in hypothyroidism

The pituitary gland is undoubtedly a target for thyroid hormone. It is the tissue with the highest density of T3 receptors and contains Type II T4 5' deiodinase which are involved in the secretion of TSH and other pituitary hormones. In the case of TSH, this knowledge has resulted in a better understanding of a number of conditions such as the adaptation to reduced thyroid reserve, and in an improvement in the way we treat hypothyroidism. But the pituitary being a target tissue for thyroid hormones has additional consequences. A direct effect of T3 on various secretions of the gland has been documented, and in the case of other pituitary hormones, directly or indirectly, thyroid hormone has some effect. T3 has a broad spectrum of metabolic and physiological effects that may, by themselves, account for a large proportion of the variability of the clinical presentation of hypothyroidism. The multiplicity of pituitary hormones and the multiplicative action of these various hormones through their target glands make the pituitary gland another key element in the variability of clinical manifestations of hypothyroidism. While this variability poses a diagnostic challenge in that hypothyroidism should be considered in a large number of conditions, the abnormalities resulting from the lack of thyroid hormone in the pituitary are equally challenging from a therapeutic point of view, since they respond promptly to the correction of the hypothyroidism. We should try to identify and treat those that are both life-threatening and not corrected rapidly by the administration of thyroid hormone.

Effects of thyroid hormones (T4,T3), bromocriptine and Triac on inappropriate TSH hypersecretion

Inappropriate TSH hypersecretion was diagnosed in a 38-year-old woman (case 1) and in a 38-year-old man (case 2). Both of them had earlier been treated by ablative therapy for hyperthyroidism. The present diagnosis was based on elevated basal serum TSH levels despite elevated serum free thyroid hormone levels. Both of them had exaggerated TSH responses to TRH (peak value 240 mU/l in case 1 and 408 mU/l in case 2). Their albumin and prealbumin levels were normal. The serum TBG level was normal in case 1 but was elevated in case 2. Serum levels of alpha-subunits of TSH, and pituitary CT scans were normal. Despite mild clinical hyperthyroidism, peripheral indices of thyroid hormone action were normal. They had also relatives with apparent resistance to thyroid hormones. In view of the possibility that prolonged pituitary thyrotrophic stimulation is detrimental, various therapeutic approaches to suppress TSH levels were tried. Both T3 and T4 treatments lowered serum TSH levels, but were poorly tolerated. Acute administration of L-dopa or bromocriptine reduced serum TSH levels, but this was not seen during long-term therapy. TRIAC treatment lowered serum TSH levels, and the drug was well tolerated. Serum TSH responses to TRH were not blunted during T3, T4 or TRIAC treatments. Somatostatin also reduced serum TSH levels, but did not potentiate the effect of low dose T3 therapy. Our results suggest that the patients had unbalanced pituitary and peripheral thyroid hormone resistance, predominantly at the pituitary level. Of the drugs studied, TRIAC seemed to be the most suitable therapy.

Non-adenomatous inappropriate TSH hypersecretion and euthyroidism requires no treatment

The syndrome of inappropriate TSH secretion is described in a euthyroid girl and her father. Based on nuclear T3 binding studies in fibroblasts, generalized tissue resistance was associated with a lower binding affinity for T3 in nuclear extracts suggestive of a structurally abnormal receptor for T3. Early recognition of the syndrome and observation of the short-term response to thyroid medication prevented unnecessary trials of antithyroid medication and later radical ablative thyroid treatment.

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.

Central hypothyroidism and hyperthyroidism

Thyroid function is maintained by tonic secretion of TSH by the pituitary. TSH secretion, in turn, is dependent on hypothalamic TRH production. Therefore, diseases of the hypothalamus and pituitary are frequently associated with TSH deficiency, producing central hypothyroidism. All patients with hypothalamic or pituitary disease should have thyroid function tests including a serum TSH by radioimmunoassay (RIA). In central hypothyroidism the TSH RIA is inappropriately low in relationship to the degree of hypothyroxinemia but is not always undetectable. In fact, because of the production of biologically inactive TSH, the TSH RIA may be in the high range of normal. Therapy of central hypothyroidism includes the management of associated pituitary hormone deficiencies, particularly secondary adrenal failure, and neurologic defects. A rare cause of hyperthyroidism is excessive TSH secretion. This may be due to a TSH-secreting pituitary tumor or to a functional disturbance in TSH secretion. TSH-secreting pituitary tumors are often large and locally invasive. Selective pituitary resistance to thyroid hormone is the most common cause of functional TSH-induced hyperthyroidism. It is important to rule out generalized thyroid hormone resistance before use of antithyroid drugs or thyroid surgery in patients suspected of this disorder. This is because antithyroid treatment is contraindicated in generalized thyroid hormone resistance.

The diagnostic challenge of euthyroid hyperthyroxinemia

In euthyroid hyperthyroxinemia high levels of thyroxine (T4) may be either transient or persistent, associated with high, normal, or low levels of tri-iodothyronine (T3). Euthyroid hyperthyroxinemia may occur: as a response to abnormal plasma binding (thyroxine binding globulin, albumin, prealbumin, or autoantibodies), because of hormone resistance, after exposure to drugs such as amiodarone, cholecystographic contrast agents, or propranolol, during acute psychiatric illness or stress, and in hyperemesis gravidarum. In some instances the cause of persistent hyperthyroxinemia still remains obscure. No single investigation (including free hormone measurement and the response of thyrotropin to its releasing hormone) can distinguish all of these entities from true hyperthyroidism. Hence, re-evaluation in cases of diagnostic uncertainty should begin with clinical reassessment. Techniques are now available to identify easily some causes of euthyroid hyperthyroxinemia, allowing us to recognise patients and relatives who are at risk of inappropriate treatment. Because measurement of serum T4 remains the key investigation for diagnosis of thyroid dysfunction, it is important to appreciate the full range of conditions that compromise its specificity.

Hyperthyroidism due to inappropriate TSH secretion with associated hyperprolactinaemia--a case report and review of the literature

A patient with inappropriate thyrotrophin (TSH) secretion is described. She initially presented with classical hyperthyroidism during pregnancy, responded to propylthiouracil and, subsequently, had a normal delivery. Hyperthyroidism persisted and 7.5 months later a subtotal thyroidectomy was performed. After a further 16 months, mild symptoms of hyperthyroidism recurred. She again responded to propylthiouracil, but developed galactorrhoea. At that stage, it was noted that she had persistently elevated circulating TSH in the presence of elevated T4 and T3 levels. Her symptomatology was mild, although objective indices of thyroid activity, including pulse rate, BMR, sex hormone binding globulin and cholesterol, were indicative of hyperthyroidism. CT scan and tomography of the sella were normal. She had a markedly exaggerated TSH response to thyrotrophin releasing hormone (TRH). Basal TSH and responsiveness to TRH was suppressed by high dose dexamethasone. The TSH response to TRH was partially suppressed by exogenous T3, but there was no effect on basal TSH levels. TSH also decreased slightly with L-dopa and bromocriptine. Circulating TSH rose markedly during methimazole administration. TSH alpha and beta subunits were elevated and appropriate for the high TSH. In addition, both subunits increased following TRH. The patient had basal hyperprolactinaemia with an impaired prolactin (PRL) response to TRH and metoclopramide. PRL suppressed with L-dopa and bromocriptine. The remaining anterior pituitary function was intact. Most of the laboratory findings argue against the presence of a TSH producing pituitary tumour and the most likely cause for inappropriate TSH secretion in this patient is selective resistance of the thyrotroph to thyroid hormones. A mild element of peripheral resistance might also be present. The hyperprolactinaemia could be related to lactotroph resistance to thyroid hormone. The complexities of treatment in this patient are stressed. Therapy was initially attempted with low dose dexamethasone, but this had no effect. T3 treatment produced an exacerbation of her symptomatology and did not influence basal TSH, thyroid hormones, or 131I uptake. Bromocriptine administration for 11 months partially suppressed basal TSH without influencing T3 and there was an increase in T4. Methimazole did decrease her T4 and T3, but TSH and PRL rose to even greater levels. Her hyperthyroidism was eventually controlled with an ablative dose of 131I. Thyroid hormone will be given in an attempt to suppress her TSH.