The consequences of inappropriate treatment because of failure to recognize the syndrome of pituitary and peripheral tissue resistance to thyroid hormone

Hypothalamic-pituitary axis and peripheral tissue responses to TRH stimulation and liothyronine suppression tests in normal subjects evaluated by current methods

OBJECTIVE

To reevaluate the responses of thyrotropin-releasing hormone (TRH) stimulation test in baseline condition as well as after the administration of graded supraphysiological doses of liothyronine (L-T(3)) in normal subjects.

DESIGN

To assess various parameters related to the hypothalamic-pituitary axis and peripheral tissue responses to L-T(3) in 22 normal individuals (median age: 30.5 years). Subjects were submitted to an intravenous TRH test at baseline condition and also to the oral administration of sequential and graded doses of L-T(3) (50, 100, and 200 microg/day), each given over 3 days, at an outpatient clinic. Blood samples were obtained for thyrotropin (TSH) and prolactin (PRL) at basal and then 15, 30, and 60 minutes after the TRH injection. Effects of L-T(3) administration on cholesterol, creatine kinase, retinol, ferritin, and sex hormone-binding globulin (SHBG) were also measured at basal and after the oral administration of L-T(3).

MAIN OUTCOME

TRH administration resulted in an increase of 4- to 14-fold rise in serum TSH (8.3 +/- 2.5-fold), and in a slight rise in serum PRL concentrations (3.8 +/- 1.5-fold). Administration of graded doses of triiodothyronine (T(3)) resulted in a dose-dependent suppression of TSH and PRL. Basal thyroxine-binding globulin (TBG) and cholesterol levels decreased, and ferritin and SHBG increased after L-T(3) administration, while creatine kinase and retinol did not change throughout the study. There was a positive correlation between basal TSH and TSH peak response to TRH at basal condition and after each sequential L-T(3) doses. On the other hand, TSH peak response to the TRH test did not predict cholesterol, TBG, ferritin, or SHBG values.

CONCLUSION

Using the current methods on hormone and biochemical analysis, we standardized the response of many parameters to TRH stimulation test after sequential and graded T(3) suppression test in normal subjects. Our data suggest that the evaluation of the responses of the hypothalamus-pituitary axis to TRH test as well as the impact of L-T(3) on peripheral tissues were not modified by the current methods.

Resistance to thyroid hormone with missense mutation (V349M) in the thyroid hormone receptor beta gene

Resistance to thyroid hormone (RTH) is a syndrome characterized by reduced sensitivity to the thyroid hormone. It is generally caused by mutations in the thyroid hormone receptor beta (TR beta) gene. On the basis of its clinical features, two different forms of this syndrome have been described: generalized resistance and pituitary resistance. A total of 122 TR beta gene mutations have been identified thus far. A 38-year-old woman presented with intermittent palpitation. Thyroid function tests revealed elevated levels of free T4 and TSH. TSH a-subunit levels were 0.41 mlU/mL, and magnetic resonance images of the sellar region evidenced no abnormal findings. The TSH response to TRH stimulation was found to be normal. The sequence analysis of the TR beta gene verified a missense mutation in exon 11, and the observed amino acid alteration was a substitution of a valine for a methionine at codon 349. We report the first case of a woman with RTH, which was found to be caused by a missense mutation (V349M) in the TR beta gene.

[Thyroid hormone resistance syndrome]

Resistance to thyroid hormone (RTH) is a syndrome characterized by elevated serum thyroid hormone (TH) levels and elevated or inappropriately normal thyrotropin levels. In general, patients exhibit TH resistance in the pituitary and peripheral tissues. The phenotype of RTH is variable; the affected individuals are clinically euthyroid or even hypothyroid depending on the severity of the mutation, the variable hyposensitivity to TH among individuals as well as in different tissues. In almost all cases the genetic basis of RTH lies in mutation of the carboxyl-terminus of the ss-thyroid hormone receptor. RTH is a dominant disorder, except in one family; most individuals are heterozygous for the mutant allele. New standard techniques and genetically engineered mouse model systems have increased our understanding on TH receptor action, in particular, how mutant thyroid receptors from RTH patients can block wild-type thyroid receptor function (dominant negative activity), and how the mutant receptors can differently affect various tissues and individuals.

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.

The Syndrome of Resistance to Thyroid Hormone, Misdiagnosed and Treated as Thyrotoxicosis

OBJECTIVE

To report two cases of resistance to thyroid hormone and to promote increased awareness of this syndrome, which is frequently misdiagnosed and incorrectly treated.

METHODS

We describe a young woman and her father, both of whom were diagnosed at a younger age as having thyrotoxicosis and were treated with thyroidectomy and radioactive iodine. Both patients later proved to have resistance to thyroid hormone and required supraphysiologic doses of levothyroxine to normalize the thyroid-stimulating hormone (TSH) while remaining euthyroid.

RESULTS

Laboratory evaluation revealed increased serum total thyroxine and triiodothyronine levels as well as normal to increased TSH levels. The free alpha sub-unit/TSH ratio was normal, and magnetic resonance imaging of the pituitary gland showed no tumor. Metabolic studies in the daughter, with use of graded doses of triiodothyronine, supported the diagnosis.

CONCLUSION

Both patients shown to have resistance to thyroid hormone were misdiagnosed and inappropriately treated in the past. The resultant hypothyroidism has been difficult to treat, particularly in the father who has coronary artery disease.

Hyperactivity and Learning Deficits in Transgenic Mice Bearing a Human Mutant Thyroid Hormone β1 Receptor Gene

Resistance to thyroid hormone (RTH) is a human syndrome mapped to the thyroid receptor β(TRβ) gene on chromosome 3, representing a mutation of the ligandbinding domain of the TRβ gene. The syndrome is characterized by reduced tissue responsiveness to thyroid hormone and elevated serum levels of thyroid hormones. A common behavioral phenotype associated with RTH is attention deficit hyperactivity disorder (ADHD). To test the hypothesis that RTH produces attention deficits and/or hyperactivity, transgenic mice expressing a mutant TRβ gene were generated. The present experiment tested RTH transgenic mice from the PV kindred on behavioral tasks relevant to the primary features of ADHD: hyperactivity, sustained attention (vigilance), learning, and impulsivity. Male transgenic mice showed elevated locomotor activity in an open field compared to male wild-type littermate controls. Both male and female transgenic mice exhibited impaired learning of an autoshaping task, compared to wild-type controls. On a vigilance task in an operant chamber, there were no differences between transgenics and controls on the proportion of hits, response latency, or duration of stimulus tolerated. On an operant go/no-go task measuring sustained attention and impulsivity, there were no differences between controls and transgenics. These results indicate that transgenic mice bearing a mutant human TRβ gene demonstrate several behavioral characteristics of ADHD and may serve a valuable heuristic role in elucidating possible candidate genes in converging pathways for other causes of ADHD.

Hormone-nuclear receptor interactions in health and disease. Thyroid hormone resistance

The syndromes of resistance to thyroid hormone (RTH) are rare disorders characterized by elevated levels of circulating free thyroid hormones, inappropriate TSH secretion and variably reduced peripheral tissue responses to iodothyronine action. On the basis of clinical features, two major forms of RTH are recognized: generalized resistance (GRTH) in which patients are asymptomatic with few clinical signs, and pituitary resistance (PRTH) where patients present with features associated with thyrotoxicosis. However, a review of the literature and our own experience indicates that there is a wide overlap of clinical and biochemical features between individuals with GRTH or PRTH. Genetic analysis shows that both disorders are associated with a number of different mutations in the thyroid hormone receptor beta (TR-beta) gene which localize to two regions in the hormone-binding domain. The mutant proteins are transcriptionally impaired but preserve the ability to bind DNA, dimerize and inhibit the function of their wild-type counterparts in a dominant negative manner. Dominant negative effects of mutant receptors within the pituitary-thyroid feedback axis generate abnormal thyroid function test results characteristic of RTH. The variable peripheral resistance may be related to differences in tissue distribution of TR-alpha versus TR-beta receptor isoforms, variable dominant negative effects of mutant receptors on different target genes or other factors not related to the receptor mutation. Although GRTH and PRTH represent the variable phenotypic spectrum of a single genetic entity, this clinical distinction will remain useful as a guide to appropriate treatment.

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.

Generalized thyroid hormone resistance due to a deletion of the carboxy terminus of the c-erbA beta receptor

Generalized resistance to thyroid hormone (GRTH) is a disorder of thyroid hormone action which has been linked to the beta thyroid hormone receptor (TR beta) gene. A diverse array of TR beta mutations have been characterized, and these distinct genotypes have been associated with characteristic patterns of severity and tissue distribution of clinical thyroid resistance. In this report, we describe a patient with GRTH caused by a single C-->A base mutation (nucleotide 1623) in one allele of TR beta (exon 10). The mutation produces a premature translation termination signal (UGA) at codon 446 and predicts expression of a mutant TR beta which is truncated by 16 carboxyl-terminal amino acids (TR beta delta 446-461). This sequence was absent in both parents, indicative of a de novo mutation in the proband. To our knowledge, this case represents the first description of a mutation producing premature translation termination of TR beta in association with the syndrome GRTH, and emphasizes the critical role of the carboxyl terminal region of TR beta in mediating both positive and negative regulation of thyroid-responsive target genes in many tissues.

The variable clinical phenotype in thyroid hormone resistance syndrome

Thyroid hormone resistance syndrome (RTH) is a rare disorder characterized by elevated levels of circulating free thyroid hormones, inappropriate TSH secretion, and reduced peripheral tissue responses to iodothyronine action. On the basis of clinical features, at least two different forms of RTH have been described: generalized resistance (GRTH) in which patients are asymptomatic with few clinical signs and pituitary resistance (PRTH) where patients present with some signs and symptoms associated with thyrotoxicosis. However, a review of the literature and our own experience indicates that there is a wide overlap of symptoms and signs exhibited by individuals with GRTH or PRTH. Assessments using biochemical and physiological indices of thyroid hormone action are useful, but limited by their lack of precision and also show an overlap between values recorded in GRTH and PRTH. In addition, we have observed significant temporal variations in clinical signs as well as in parameters of thyroid hormone action in the same individuals, with no correlation with their subjective symptoms. Recent genetic analyses indicate that patients with either GRTH or PRTH are heterozygous for mutations in the thyroid hormone receptor beta (TR beta) gene. Indeed, different clinical features have been observed in affected individuals within a kindred harboring the same Tr beta mutation, and identical mutations have been identified in unrelated kindreds classified as GRTH or PRTH. These data support the view that GRTH and PRTH are variable manifestations of a single genetic entity. Nevertheless, this clinical distinction will remain useful as a guide to the most appropriate treatment. The variable phenotypic spectrum of thyroid hormone resistance may be related to factors other than mutations in Tr beta that have yet to be elucidated.

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.

Spectrum of serum thyroglobulin elevation in congenital thyroid disorders

Serum thyroglobulin (Tg) data are presented for 47 infants with congenital thyroid disorders. Abnormal elevation of serum Tg (> 250 micrograms/L) occurred in 17% of the population studied, whereas values in excess of 1,000 micrograms/L were demonstrated in 11% of infants. The latter group includes the first report of supraphysiologic Tg elevation in an infant with thyroid gland ectopia, and the highest reported thyroglobulin level in the syndrome of generalized thyroid hormone resistance in an infant homozygous for a novel deletion in the c-erbA beta receptor. Mechanisms involved in the pathogenesis of Tg elevation are discussed. We conclude that Tg elevation in congenital thyroid disorders is more common than previously recognized, and values > 1,000 micrograms/L identify infants with a spectrum of anatomic and biochemical abnormalities.

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)

Screening of nineteen unrelated families with generalized resistance to thyroid hormone for known point mutations in the thyroid hormone receptor beta gene and the detection of a new mutation

Generalized resistance to thyroid hormone (GRTH) is a syndrome characterized by impaired tissue responsiveness to thyroid hormone. Two distinct point mutations in the hormone binding domain of the thyroid hormone receptor (TR) beta have recently been identified in two unrelated families with GRTH. One, Mf, involves a replacement of the normal glycine-345 for arginine in exon 7 and another, Mh, replaces the normal proline-453 for histidine in exon 8. To probe for the presence of the Mf and Mh defect in 19 unrelated families with GRTH, we applied separate polymerase chain reactions using allele-specific oligonucleotide primers containing the normal and each of the two mutant nucleotides at the 3'-position. A total of 24 affected subjects and 13 normal family members were studied. The mode of inheritance was dominant in 13 families, was unknown in 5 families, and was clearly recessive in 1 family in which only the consanguineous subjects were affected. Primers containing the substitutions specific for Mf and Mh amplified exons 7 and 8, respectively, only in affected members of each of the two index families. Primers containing the normal sequences amplified exons 7 and 8 of the TR beta gene in all subjects except affected members of one family. In this family with recessively inherited GRTH, neither exon could be amplified using any combinations of primers and DNA blot revealed absence of all coding exons. These results indicate a major deletion of the TR beta gene, including both DNA and hormone binding domains. Since heterozygous members of this family are not affected, the presence of a single normal allele is sufficient for normal function of the TR beta. These data also support the hypothesis that in the dominant mode of GRTH inheritance the presence of an abnormal TR beta interferes with the function of the normal TR beta. Distinct mutations are probably responsible for GRTH in unrelated families.

Erythrocyte zinc in hyperthyroidism: reflection of integrated thyroid hormone levels over the previous few months

Red blood cell (RBC) zinc (Zn) concentration was measured by atomic absorption spectrophotometry in 28 healthy volunteers, in 46 patients with hyperthyroidism, and in 6 patients with hypothyroidism. The mean (+/- SD) RBC Zn concentration in euthyroid controls was 11.4 +/- 1.5 mg/L RBC, and the normal range defined as the mean +/- 2 SD was 8.5 to 14.3 mg/L RBC. The mean RBC Zn in patients with hyperthyroidism was decreased to 6.4 +/- 1.6 mg/L RBC, and 43 (93%) had low values. The mean RBC Zn in patients with hypothyroidism was not different from that in the controls. There was a significant negative correlation between the concentrations of RBC Zn and those of both plasma thyroxine (T4; r = -0.73) and plasma 3,5,3'-triiodothyronine (T3; r = -0.70). After the treatment of 17 hyperthyroid patients with antithyroid drugs, both mean plasma T4 and T3 levels became normal within 4 weeks, but the normalization of RBC Zn lagged about 2 months behind them. The RBC Zn levels significantly correlated with both the plasma T4 and T3 levels obtained 0, 4, 8, and 12 weeks prior to the RBC sampling, and the highest correlation was observed between the RBC Zn levels and plasma T4 and T3 levels measured 8 weeks previously. These data suggest that RBC Zn concentration in hyperthyroid patients reflects a patient's mean thyroid hormone level over the preceding several months as glycosylated hemoglobin level does in diabetic patients.

Generalized resistance to thyroid hormone associated with a mutation in the ligand-binding domain of the human thyroid hormone receptor beta

The syndrome of generalized resistance to thyroid hormone is characterized by elevated circulating levels of thyroid hormone in the presence of an overall eumetabolic state and failure to respond normally to triiodothyronine. We have evaluated a family with inherited generalized resistance to thyroid hormone for abnormalities in the thyroid hormone nuclear receptors. A single guanine----cytosine replacement in the codon for amino acid 340 resulted in a glycine----arginine substitution in the hormone-binding domain of one of two alleles of the patient's thyroid hormone nuclear receptor beta gene. In vitro translation products of this mutant human thyroid hormone nuclear receptor beta gene did not bind triiodothyronine. Thus, generalized resistance to thyroid hormone can result from expression of an abnormal thyroid hormone nuclear receptor molecule.

Interpretation of thyroid function tests

The development of radioimmunoassays over the past 20 years has expanded our knowledge of thyroid physiology and improved our management of thyroid disease. The use of these tools in neonatal screening for congenital hypothyroidism alone has reduced the incidence of mental retardation in the industrialized world. Based on an accurate physical examination, the judicious use of immunoassays for thyroxine, triiodothyronine, and thyrotropin and the use of thyroglobulin and thyroid microsomal antibodies will allow the general physician to confidently delineate common thyroid disorders in the great majority of patients. The additional use of an ultrasensitive thyrotropin assay, thyroid scans, and fine-needle aspiration biopsy will complete the accurate diagnosis of the great majority of thyroid diseases. The ultrasensitive thyrotropin assay may become the universal thyroid function test. The major pitfalls in the use of these tests lies in the variable effect chronic illness has on the most frequently used tests: thyroxine and triiodothyronine. Tests for these thyroid hormones, which in the relatively well outpatient are highly accurate, may in the ill, hospitalized patient become very misleading.

Thyroid hormone resistance in a large kindred: physiologic, biochemical, pharmacologic, and neuropsychologic studies

PURPOSE

Thyroid hormone resistance affects the pituitary gland and a variety of other tissues. We studied a large kindred with this disorder and measured a number of clinical markers of tissue metabolism to determine if these markers were useful in elucidating the sites and degree of resistance.

PATIENTS

A kindred of 89 persons in four generations was identified; 44 had thyroid function tests, and 14 (five to 67 years old) were found to have thyroid hormone resistance.

RESULTS

The inheritance pattern was autosomal dominant, with no common HLA haplotype. Physiologic measurements in five affected members showed marked heterogeneity. Four patients had normal baseline cardiac contractility, but only two experienced a shortening of their QKd interval into the hyperthyroid range with triiodothyronine (T3) therapy. Intrathyroidal 127I content was increased in two patients and was normal in two. Bone mineral content was normal in two men, but two women had marked osteopenia. The propositus, hypothyroid after inappropriate 131I therapy, had a hypothyroid ventilatory response to hypercapnea. This response became low normal during T3 (100 micrograms/day) administration but not during long-term thyroxine (T4) (300 micrograms/day) administration. Three other patients had values within normal limits and one had a hyperthyroid ventilatory response. Peripheral biochemical markers of thyroid hormone action were measured in 13 affected and 19 unaffected family members. Sex hormone-binding globulin was increased in zero of 13 affected patients (versus 19 of 20 hyperthyroid, chi 2:p less than 0.001); ferritin was elevated in two of 13 patients (versus 11 of 20 hyperthyroid, p less than 0.02); angiotensin converting enzyme activity was increased in one of 13 patients (versus 12 of 20 hyperthyroid, p less than 0.025). The eldest patient had marked cardiac sensitivity despite normal biochemical markers. We attempted to suppress the integrated thyroid-stimulating hormone (TSH) response to thyrotropin-releasing hormone (TRH) using T3 (72 and 100 percent suppression in two patients), dopamine (40 percent suppression in one), 3,5,3'-triiodothyroacetic acid (TRIAC) (94 percent suppression in one), and verapamil (10 percent and 40 percent suppression in two). Neuropsychologic function was studied in 14 individuals (11 affected, three unaffected). Although mild impairments were detected, they were not specific for thyroid hormone resistance.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Familial generalized resistance to thyroid hormones: report of three kindreds and correlation of patterns of affected tissues with the binding of [125I] triiodothyronine to fibroblast nuclei

We here report three kindreds with a total of 19 persons affected with central and peripheral resistance to thyroid hormones: one kindred with 10 affected persons is the largest reported to date. Male to male transmission of the syndrome was evident in two kindreds, consistent with an autosomal dominant mode of inheritance. During several years of follow up, the degree of resistance to thyroid hormones did not ameliorate. Within a given kindred, a given tissue or tissues was consistently more resistant to thyroid hormone than other tissues. The pattern of tissues most affected in one kindred differed from that of another kindred, perhaps reflecting the inherited underlying molecular defects. Members of kindred A frequently had bone involvement, and several had learning disabilities and recurring infections, while most members of kindreds B and C had little bone involvement, but marked hepatic and cardiac resistance to thyroid hormones. Kinetic studies of the binding of [125I] triiodo-L-thyronine to nuclei from skin fibroblasts from affected patients from each of the kindreds demonstrated decreased maximum binding as compared to normal fibroblasts, but there was no correlation between this parameter and other features of the disease. Four of the 19 patients had previously been treated inappropriately with antithyroid therapies, demonstrating how the syndrome may be readily confused with Graves' disease by some clinicians. Behavior or school performance improved in all children treated with thyroid hormones, and a growth spurt was documented in six children, but objective improvement in IQ scores was not demonstrated, suggesting that initiation of hormone therapy at an early age may be important for maximum benefit.

Hyperthyroidism. Causes, clinical features, and diagnosis

The usual patient with hyperthyroidism has Graves' disease: If serum levels of thyroid hormone are clearly elevated, the presence of infiltrative ophthalmopathy or pretibial myxedema is probably sufficient for establishing the diagnosis. However, if the ancillary findings of Graves' are not present, the radioactive iodine uptake should be determined to rule out other possible etiologies of hyperthyroidism. Signs of hyperthyroidism may be subtle or misleading, particularly in the elderly; the well-informed clinician keeps the diagnosis in mind, and if the initial thyroid hormone tests are not definitive, employs additional tests that are cost-effective in the individual clinical situation.

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.