Lithium-associated transient thyrotoxicosis in 4 Chinese women with autoimmune thyroiditis

Four Chinese female patients who suffered from manic-depressive disorder and underlying autoimmune thyroiditis developed transient episodes of thyrotoxicosis during maintenance lithium therapy. Endocrinologically speaking, three of them had "Hashitoxicosis", while the other had silent lymphocytic thyroiditis. Albeit rare among Western patients, such lithium-associated thyroid dysfunctions appeared to be more likely to occur in Hong Kong Chinese. They seemed to involve multiple aetiological factors, such as autoimmune thyroid disease, the toxic and immunomodulatory roles of lithium and perhaps genetic and dietary factors. Because of their self-limiting nature, the importance of avoiding unnecessary and potentially deleterious antithyroid treatment is emphasised.

Long term follow-up of treated hyperthyroid and hypothyroid patients

The objective was to assess the success rate in patients receiving surgery or radioactive iodine for primary hyperthyroidism and the incidence of subsequent hypothyroidism. A long term follow up of patients on L-thyroxine has also been performed from a cohort of patients on the Tayside Thyroid Register. The case series has been followed-up for up to 21 years. 2,038 patients were registered of whom 90.1% were female. 1,045 had had previous hyperthyroidism and 993 had hypothyroidism. Treatment for thyrotoxicosis varied with age, 80.4% of patients under the age of 40 being treated by thyroidectomy and 72.6% of patients over 50 being given the iodine. Overall 9% of patients required medical therapy alone (carbimazole), and this varied little with age. Compared to radioactive iodine, thyroidectomy was more successful (90.2% vs 82.9%, p < 0.01) and had a lower rate of subsequent hypothyroidism (22.0% vs 47.6% at 5 years, p < 0.001). Of patients treated with radioactive iodine, those who were unsuccessful had received a lower dose (mean 354MBq vs 489MBq, p < 0.001). Of patients receiving L-thyroxine (n = 1,180), 58.5% had a suppressed level of thyroid stimulating hormone, 38% had a detectable but not elevated level, and 3.5% had an elevated level (> 4.0 mU/l). Patients with a suppressed level were taking a higher dose of L-thyroxine than those with a detectable level (114.2 +/- 56.9 micrograms vs 100.4 +/- 45.9 micrograms, p < 0.01), but those with an elevated level were prescribed an even higher mean L-thyroxine dose (137.1 +/- 58.8 micrograms)); many were probably poorly compliant.(ABSTRACT TRUNCATED AT 250 WORDS)

Gestational thyrotoxicosis and hyperemesis gravidarum: possible role of hCG with higher stimulating activity

OBJECTIVE

The thyroid gland is physiologically stimulated in normal early pregnancy. However, clinical thyrotoxicosis in normal pregnancy has not been well described. In order to clarify this we examined thyroid function and thyrotoxic symptoms in relation to emesis in normal pregnancy. We also investigated the possible mechanism of gestational thyrotoxicosis.

DESIGN

Thyroid function was evaluated in view of the clinical thyrotoxic symptoms and the severity of gestational emesis in early pregnancy of 51 normal women. Two pregnant women who showed clinical thyrotoxicosis were followed serially during and after pregnancy.

MEASUREMENTS

Serum free T4, free T3 and TSH were measured by radioimmunoassay and hCG by fluoroimmunoassay. Thyroid-stimulating activity of pregnancy sera was measured by cAMP increase in cultured FRTL-5 cells.

RESULTS

Fifty-one pregnant women were divided into three groups: those without emesis (n = 24), with emesis (n = 19) and with hyperemesis (n = 8). Serum free T4 and free T3 were higher in the hyperemesis group (P < 0.01) and the emesis group (P < 0.01), and serum TSH was suppressed to less than 0.1 mU/l in both groups, while serum hCG was not significantly different among these three groups. However, serum thyroid-stimulating activity was remarkably high in the hyperemesis group (P < 0.01). Thus the ratio of thyroid-stimulating activity to hCG was higher in the hyperemesis group (P < 0.05) and the emesis group (P < 0.05) compared with that in the group without emesis. These thyroid-stimulating activities were abolished by treatment of the serum with anti-hCG antibody. Two of eight women with hyperemesis, who had the highest free T4 and thyroid-stimulating activity/hCG ratio, showed overt clinical symptoms of thyrotoxicosis; all the symptoms disappeared in association with a fall in thyroid-stimulating activity and free T4.

CONCLUSION

Clinical thyrotoxicosis is caused by circulating hCG with higher biological activity in pregnant women with hyperemesis. A new clinical entity of 'gestational thyrotoxicosis' is proposed and tentative characteristics are discussed.

[Lithium and hyperthyroidism]

The development of hypothyroidism and the forming of a goiter are well-known complications associated with lithium medications. But there are also occasional references to cases of hyperthyroidism in the wake of both continual and of discontinued lithium medication. In the case being reported on here of a lady patient aged 64 and suffering from a toxic adenoma not recognized at the time, thyrotoxicosis accompanied by above-normal FT-3 results and the characteristic clinical symptoms developed when lithium medication was discontinued. Medical literature consulted in the context discussed pharmacological mechanisms which may be responsible for the said complications.

Serum markers of type I collagen formation and degradation in metabolic bone disease: correlation with bone histomorphometry

Type I collagen makes up more than 90% of bone matrix. Therefore, analysis of antigens related to collagen formation and degradation in bone should provide good and specific estimates of both bone resorption and bone formation rates. In this study we measured serum levels of the pyridinoline cross-linked telopeptide domain of type I collagen (ICTP) as a marker of bone resorption and serum carboxy-terminal propeptide of type I procollagen (PICP) as a marker of bone formation. Serum levels of the two antigens were correlated to histomorphometric indices of bone resorption and bone formation calculated from iliac crest bone biopsies in a group of 18 individuals with high- and low-turnover bone disease (myxedema, primary hyperparathyroidism, and thyrotoxicosis). After logarithmic transformation the regression of S-ICTP on volume-referent resorption rate (BRs/R/BV) was significant (r = 0.61, p < 0.01, SEM/Y = 56%). S-ICTP also showed a significant regression on the volume-referent cancellous bone balance (r = -0.45, p < 0.05, SEM/Y = 412%). S-PICP was significantly correlated to the mineral appositional rate (r = 0.53, p < 0.05) and volume-referent bone formation rate (r = 0.61, p < 0.01, SEM/Y = 48%). The correlation to bone turnover as expressed in the activation frequency was also highly significant (r = 0.61, p < 0.01, SEM/Y = 51%). No significant correlation with wall thickness or bone balance was demonstrable per remodeling cycle. Thus, assays employing antigens that reflect collagen formation and degradation are useful instruments for the evaluation of rates of bone remodeling in metabolic bone disease.

[Cytochemical definition of oxidation-reduction enzyme activity peripheral blood lymphocytes in patients with thyrotoxic goiter]

In patients with thyrotoxic goiter (TTG), a significant decrease in the activity of alpha-glycerophosphate-dehydrogenase and adenosinetriphosphatase of the peripheric blood lymphocytes was revealed. The lowest indices were noted in patients with a severe form of TTG, who underwent strumectomy. After conservative and operative treatment of TTG, a tendency for normalization of the enzyme activity was observed. Study of changes in the activity of the oxidation-reduction lymphocytic enzymes in dynamics permits to assess the severity of the course of TTG and to control and predict the effectiveness of treatment as well.

Adjunctive cholestyramine therapy for thyrotoxicosis

OBJECTIVE

Initial therapy of thyrotoxicosis usually includes beta-blockade for symptom relief and thionamides to block new thyroid hormone synthesis. In view of the increased enterohepatic circulation of thyroxine (T4) and triiodothyronine (T3) in thyrotoxicosis, we proposed that cholestyramine, an anion exchange resin which binds iodothyronines, when used adjunctively with thionamides and a beta-blocker, would lower serum iodothyronine levels faster than would standard therapy alone.

DESIGN

A double blind placebo-controlled cross-over design was used with patients randomly assigned to either the treatment or control groups. They received their initial treatment for two weeks (Phase 1) followed by a one-week washout period, and then crossed to the opposite treatment for two weeks (Phase 2). Standard therapy included atenolol 50 mg daily, individualized dosages of methimazole and either 4 g of cholestyramine or 4 g of placebo powder four times per day.

PATIENTS

Fifteen patients with thyrotoxicosis (14 Graves' disease, 1 toxic adenoma) participated in this study.

MEASUREMENTS

Total and free thyroxine and triiodothyronine, as well as thyroid-stimulating immunoglobulin and thyrotrophin-binding inhibitory immunoglobulin, were measured weekly.

RESULTS

Seven patients received cholestyramine and eight patients received placebo during Phase 1. A more rapid decline in all thyroid hormone levels was seen in the cholestyramine-treated group (F = 4-7, P < 0.01) than in the placebo group (F = 2-3.1, P = 0.05). In Phase 2, the eight patients who received cholestyramine showed an additional decline in free thyroxine from weeks one to two, but the overall rate of decline in hormone levels was not different between the groups. Immunoglobulin levels remained unaffected regardless of group, treatment, or time.

CONCLUSIONS

We conclude that cholestyramine is a safe and effective adjunctive agent in the treatment of thyrotoxicosis and that its greatest efficacy may be during the first few weeks of treatment.

Crucial role of serum human chorionic gonadotropin for the aggravation of thyrotoxicosis in early pregnancy in Graves' disease

Thyrotoxicosis in Graves' disease is often aggravated in early pregnancy and is closely associated with postpartum recurrence of stimulative thyrotoxicosis. To examine whether thyroid-stimulating TSH receptor antibody (TSAb) or human chorionic gonadotropin (hCG), which also has thyroid-stimulating activity (TSA), was responsible for this early aggravation, the respective TSA due to TSAb or hCG was evaluated by a highly sensitive cAMP accumulation assay using FRTL-5 cells. TSA was detectable in all of 11 women in normal early pregnancy, correlated positively with serum hCG concentration, and was abolished completely by the pretreatment of serum sample with the solid-phase hCG antibody coupled with Sepharose 4B. The model serum samples of Graves' disease with pregnancy were made by the mixture of normal pregnant and Graves' sera, and their TSA were reduced by the pretreatment with the solid-phase hCG antibody, just corresponding with the reduction in hCG-induced TSA. TSA of early pregnant sera in 20 patients with Graves' disease decreased significantly but were still positive even after the pretreatment with the hCG antibody. Serial changes in TSAb and hCG-induced TSA were measured in 5 of these 20 pregnant patients. hCG-induced TSA increased associated with the increase in free thyroxine, while TSAb did not show striking change in early pregnancy. These data indicate that (1) respective TSA due to TSAb or hCG can be measured distinctively by using the solid-phase hCG antibody and (2) hCG plays a crucial role in the aggravation of Graves' thyrotoxicosis in early pregnancy.

A simple method for quantitation of insulin sensitivity and insulin release from an intravenous glucose tolerance test

Both insulin secretion and insulin sensitivity are important in the development of diabetes but current methods used for their measurements are complex and cannot be used for epidemiological surveys. This study describes a simplified approach for the estimation of first phase insulin release and insulin sensitivity from a standard 40-min intravenous glucose tolerance test (IVGTT), and compares these parameter estimations with the sophisticated minimal model analysis of a frequently sampled 3-h IVGTT and the euglycaemic clamp technique. For the simplified IVGTT, first phase insulin release was measured as the insulin area above basal post glucose load unit-1 incremental change (i.e. peak rise) in plasma glucose over 0-10 min, and insulin sensitivity as a rate of glucose disappearance (Kg) unit-1 insulin increase above basal from 0-40 min post-glucose load in 18 subjects who were studied twice, either basally or in a perturbed pathophysiological state (i.e. pre- and post-ultramarathon race, n = 5; pre- and post-20 h pulsatile hyperinsulinaemia, n = 8; pre- and post-thyrotoxic state, n = 5). A further 12 subjects were compared by IVGTT, and glucose clamp. In addition, seven dogs were studied three times by IVGTT during normal saline infusion and after short-term (1/2 hour) or long-term (72 hour) adrenaline infusions. First phase insulin release and insulin sensitivity estimated from the simplified IVGTT as calculated by the two methods correlated closely (rs = 0.89 and rs = 0.87, respectively), although less precisely in markedly insulin-resistant subjects and the slopes and y intercepts of the linear regression lines were similar in the basal and perturbed states.(ABSTRACT TRUNCATED AT 250 WORDS)

[Analysis of circulating thyroid-stimulating activities in pregnant women with Graves' disease: differential measurement of activities induced by TSH receptor antibody and hCG]

Thyrotoxicosis in Graves' disease is often aggravated in early pregnancy and this aggravation is associated with postpartum relapse of thyrotoxicosis. To examine whether thyroid-stimulating TSH receptor antibody (TSAb) or human chorionic gonadotropin (hCG), which also has thyroid-stimulating activity (TSA), is responsible for this early aggravation, the respective TSA due to TSAb or hCG were evaluated with a sensitive cAMP accumulation assay using FRTL-5 cells. TSA, which was detectable in all of 11 women in normal early pregnancy, correlated positively with serum hCG level, but was abolished completely by the pretreatment of serum samples with the solid-phase hCG antibody coupled with Sepharose-4B. Total TSA in the model samples of mixture of Graves' and pregnant sera (Gr + Preg), was reduced by the pretreatment with the solid-phase antibody, just corresponding with the reduction in hCG-induced TSA. Total TSA in early pregnant sera in 15 patients with Graves' disease, decreased significantly but was still positive even by the pretreatment with the hCG antibody. Pregnancy-associated changes in TSA was examined serially in a patient with Graves' disease, and hCG-induced TSA increased predominantly along with the serum thyroid hormone in early aggravation period. These data indicate that (1) the respective TSA due to TSAb or hCG can be differentially measured by using the solid-phase hCG antibody and (2) hCG plays an important role for aggravation of Graves' thyrotoxicosis in early pregnancy.

Thyrotoxicosis with low serum total T3 level in patients with destructive thyroiditis and non-thyroidal illness

The serum total T3 level, evaluated in 687 patients with thyrotoxicosis diagnosed by an elevated serum free T4 level and suppressed serum TSH level, was found to be high in 98.1% and normal in 1.9% of 592 patients with Graves' hyperthyroidism, and high in 75.8%, normal in 21.1% and low in 3.2% of 95 patients with destructive thyroiditis. Non-thyroidal illness was found in about a third of the patients with thyrotoxicosis and a normal serum total T3 level. The serum total T3 level was low with elevated serum thyroglobulin and reverse T3 levels in three patients with severe non-thyroidal illness, in whom the thyroidal radioactive iodine uptake was suppressed and the thyrotoxicosis resolved spontaneously with a normalization of the serum total T3 level after recovery from the destructive thyroiditis and non-thyroidal illness. It is therefore concluded that thyrotoxicosis with a low serum total T3 level, partially due to associated non-thyroidal illness, is more frequently found in patients with destructive thyroiditis than in those with Graves' hyperthyroidism.

Increased plasma 5 alpha-androstane-3 alpha,17 beta-diol glucuronide concentration in clinically euthyroid women with suppressed plasma thyrotropin levels: further evidence for generalized tissue overexposure to thyroid hormones in these subjects

It has been reported that plasma levels of 5 alpha-androstane-3 alpha,17 beta-diol glucuronide (ADG) are increased in thyrotoxic patients. The present study was carried out to determine whether in clinically euthyroid subjects with suppressed TSH levels, ADG plasma levels would also be increased, suggesting a more generalized tissue overexposure to thyroid hormones. The latter has been suggested from increased sex hormone-binding globulin levels (SHBG) in these subjects. ADG and SHBG levels were measured in a group of 20 euthyroid postmenopausal women, 20 postmenopausal women with clinically evident thyrotoxicosis, and 16 euthyroid postmenopausal women with suppressed TSH levels. The mean ADG level in the thyrotoxic group was 4 times the mean level in the control group, whereas in the group with isolated TSH suppression the mean level was about twice the level in the control group. As levels of dehydroepiandrosterone sulfate, the major precursor of plasma ADG, were not significantly increased in these subjects, these data suggest an increased conversion of dehydroepiandrosterone sulfate to ADG. Together with the increased SHBG levels observed in both thyrotoxic and euthyroid subjects with suppressed serum TSH concentrations, these data support the concept that the TSH-suppressed euthyroid subjects have generalized increased thyroid hormone effects on peripheral tissues.

Biogenic amines and thyrotoxicosis

Circulating levels of T3, T4, gamma-amino-butyric acid, glutamate, 5-hydroxytryptamine, histamine, monoamine oxidase and histaminase were studied in 45 (25M, 20F) hyperthyroid patients and 46 (25M, 21F) normal healthy volunteers. Increased levels of blood 5-hydroxytryptamine, histamine and glutamic acid were observed along with elevated T3 and T4, whereas plasma gamma-aminobutyric acid, monoamine oxidase and histaminase activities were found to be low in both male and female patients. After three months of treatment, circulating levels of 5-hydroxytryptamine, histamine and glutamic acid decreased significantly along with normalization of thyroid hormones and with an increase in the concentrations of gamma-aminobutyric acid, monoamine oxidase and histaminase. There was a positive correlation between these amines and thyroid hormone levels. The findings thus suggest that alterations in the metabolism of biogenic amines may be related to an altered metabolism in thyrotoxicosis, and these parameters may prove to be useful markers for diagnosis and follow-up of these patients.

[The clinical significance of the sulfhydryl groups in the peripheral blood lymphocytes of patients with thyrotoxic goiter]

A study of 42 patients with thyrotoxic goiter revealed a reduction of SH groups in the peripheral blood lymphocytes. The reduction depended on the severity of the pathological process. Changes of the SH groups are an informative criterion of the severity of the disease and treatment efficacy.

Occupational thyroid disease

A case of thyrotoxicosis due to the occupational exposure to cosmetics in a 35-year-old beautician is reported. The hormonal pattern was consistent with exogenous thyroid hormone administration, but not with iodine hyperthyroidism. The patient denied she was using thyroid hormones; also, she lacked the typical features of patients with thyrotoxicosis factitia. Her occupational history was carefully reviewed: A heavy exposure of the unprotected skin to cosmetic creams containing iodine, thyroid hormones, and thyroid extracts had occurred in the previous months. The patient was advised to refrain from the exposure, and a persistent remission of thyrotoxicosis was observed thereafter. This case suggests that percutaneous absorption of thyromimetic substances though never described before, may occur in an occupational setting. We advise that such cosmetics be handled with care, not only by patients with thyroid disease but by euthyroid subjects as well; close medical surveillance over the use of such preparations seems appropriate.

Increase of serum somatomedin C in hyperthyroid patients with pregnancy

In thyrotoxic women with pregnancy, serum somatomedin C (SmC) concentration was markedly elevated (mean +/- SD 13.57 +/- 4.66 U/ml) compared to thyrotoxic women without pregnancy (1.24 +/- 1.09 U/ml), non-pregnant euthyroid women previously treated for hyperthyroidism (0.87 +/- 0.30 U/ml), normal subjects with pregnancy (6.08 +/- 3.36 U/ml) and pregnant euthyroid women previously treated for hyperthyroidism (5.98 +/- 1.52 U/ml). Since SmC/growth hormone ratio was significantly more in thyrotoxic pregnant women than in normal pregnant women and euthyroid pregnant women previously treated for hyperthyroidism, and since human placental lactogen (HPL), human chorionic gonadotropin (HCG) and prolactin (PRL) do not crossreact with SmC antibody, it is suggested that excess thyroid hormone during pregnancy results in excessive hepatic somatomedin C production.

Thyroid-stimulating antibodies and thyroid stimulation-blocking antibodies during the pregnancy and postpartum period: a case report

This report describes a unique pattern of changes in thyroid function and thyroid antibodies in a woman during the course of two pregnancies and two postpartum periods. A 25-year-old woman developed hypothyroidism in the postpartum period after the delivery of her first child. She was found to have potent thyroid stimulation-blocking antibodies (TSBAb) in the serum. One year later, she became pregnant again, and during the pregnancy, TSBAb had decreased to an undetectable level. She gave birth to the second healthy child and developed postpartum thyrotoxicosis, probably due to destruction of the thyroid gland, which gradually resolved. In this postpartum period, serum TSBAb levels increased. Eight months postpartum, she developed what appeared to be Graves' disease with an elevated 123I-thyroid uptake. Serum thyroid-stimulating antibodies (TSAb) were found at that time, and the TSBAb had disappeared from her serum.

Thyrotoxicosis and hyperemesis gravidarum associated with a serum activity which stimulates human thyroid cells in vitro

OBJECTIVE

To investigate in-vitro thyroid stimulatory activity in the serum of patients with hyperemesis gravidarum and thyrotoxicosis.

DESIGN

Serum from hyperthyroid patients was incubated with cultures of human thyroid cells. Attempts were made to neutralize stimulatory activity with antisera to hCG.

PATIENTS

Five patients presenting in early pregnancy with hyperemesis and thyrotoxicosis.

MEASUREMENTS

Serum concentrations of thyroid hormones (total and free), TSH and hCG. Accumulation of extracellular cAMP in response to serum.

RESULTS

All five patients had biochemical hyperthyroidism with no evidence of an underlying autoimmune disease. The mean cAMP accumulation over 4 hours with sera from 12 non-pregnant controls was 130.6 (121.8-142.8), from 12 pregnant controls 132.4 (118.1-143.8), compared with values of 144.7, 159.1, 166.2, 178.9 and 320.5 for the thyrotoxic patients. The stimulatory activity could not be neutralized by addition of anti-hCG or by depleting the sera of hCG.

CONCLUSIONS

Thyrotoxicosis may present with hyperemesis in early pregnancy. Clinical and biochemical features may be masked by the pregnancy or by the intercurrent illness. The hypothesis that hCG is a thyroid stimulator in patients with hyperemesis gravidarum is not supported by the immuno-neutralization data in this study.

The effects of common matrices for assay standards on performance of 'ultra sensitive' immunometric assays for TSH. Report of a joint WHO/IFCC collaborative study

This report describes the results of a collaborative study organized by a joint working group of IFCC and WHO and involving nine manufacturers of TSH immunometric assay kits. The study was designed to determine whether a calibrator with a common matrix gives better between-laboratory agreement for calibration of serum samples than the various kit calibrators, and to assess various materials for their suitability for use as common matrices. Kit calibrators or calibrators consisting of the IRP for TSH made up in two common matrices, (1) serum from patients with untreated thyrotoxicosis or (2) serum taken from subjects treated with suppressive doses of triiodothyronine, gave similar results for the between-laboratory variation of estimates of TSH concentration for a range of serum samples. Dose-response curves for the two calibrators in 'common' matrices were similar to one another and to those for the kit calibrator. However, the occurrence of non-specific serum effects is shown by the comparison of results for these calibrators with results for calibrators made up in a third common matrix, serum treated with wheat germ lectin. Dose-response curves for this calibrator were dissimilar to those for the other calibrators and between-laboratory variation for estimates in terms of this latter calibrator showed a substantial increase. Moreover, although the between-laboratory variances for estimates of the TSH concentration in terms of each of these calibrators (except those made up in serum treated with in the wheat germ lectin) were similar for any one sample from five hyperthyroid patients, the variances were not consistent between samples, even for samples with similar mean TSH concentrations. These results suggest that a major factor in the between-laboratory variation, especially in the region near 'zero dose', is sample-related, and is caused by particular samples interacting differently with different assay systems. In general, it would appear that for the well controlled 'ultra-sensitive' TSH immunometric assay kits, included in this study, between-laboratory agreement of estimates of the TSH concentration in serum samples is not likely to be substantially improved by use of a common matrix for the standards.

In vivo and in vitro sodium pump activity in subjects with thyrotoxic periodic paralysis

OBJECTIVE

To examine whether sodium pump activity plays a part in the pathogenesis of thyrotoxic periodic paralysis.

DESIGN

Measurement of platelet sodium-potassium ATPase and in vivo sodium pump activities in healthy subjects and thyrotoxic subjects with and without paralysis.

SETTING

University hospital in Hong Kong.

SUBJECTS

21 healthy subjects, 23 untreated thyrotoxic subjects, 13 untreated men with periodic paralysis, seven treated thyrotoxic subjects, and six treated men with periodic paralysis.

MAIN OUTCOME MEASURES

Platelet Na+, K(+)-ATPase activity and plasma rubidium concentration after oral loading.

RESULTS

Median (range) platelet Na+, K(+)-ATPase activity in thyrotoxic subjects was 253 (169-821) mumol inorganic phosphate/h/g protein--significantly higher than that in healthy subjects (134 (81-180) mumol/h/g protein; p less than 0.001). Na+, K(+)-ATPase activity in those with periodic paralysis was 374 (195-1196) mumol/h/g protein, again significantly higher than that in healthy subjects (p less than 0.001) and that in other thyrotoxic subjects (p less than 0.01) despite similar degrees of hyperthyroidism. Activities in treated thyrotoxic subjects with and without periodic paralysis were 148 (110-234) and 131 (86-173) mumol/h/g protein respectively. Mean (95% confidence interval) plasma rubidium concentration five hours after oral administration in thyrotoxic subjects (7.0 (6.6 to 7.5) mumol/l) was significantly lower than in healthy subjects (10.2 (9.5 to 10.9) mumol/l; p less than 0.001) and higher than in those with periodic paralysis (6.0 (5.7 to 6.3) mumol/l; p less than 0.01).

CONCLUSIONS

Sodium pump activity in untreated subjects with periodic paralysis is higher than in other thyrotoxic subjects, and this may be responsible for the hypokalaemia.

Incidence, predictability, and pathogenesis of amiodarone-induced thyrotoxicosis and hypothyroidism

PURPOSE

To determine the incidence and predictability and to elucidate the pathogenesis of amiodarone-induced thyrotoxicosis (AIT) and hypothyroidism (AIH).

PATIENTS AND METHODS

A prospective study was performed in 58 consecutive euthyroid patients living in an area with moderately sufficient iodine intake, who had never been treated for thyroid disease and who started amiodarone therapy for the first time.

MAIN OUTCOME MEASURES

Development of thyrotoxicosis or hypothyroidism.

RESULTS

The follow-up period was 6 to 54 months (mean, 21 months). The incidence of AIT was 12.1%. A steady occurrence of new cases was observed. The development of AIT was unpredictable and of unexplained sudden onset. The incidence of AIH was 6.9%. All AIH cases occurred early in the course of amiodarone therapy. The development of AIH was related to pre-existent thyroid disease: the relative risk for women with microsomal and/or thyroglobulin autoantibodies prior to treatment was 13.5 (95% confidence interval 3.2 to 57.4). The development of AIT or AIH was not related to the extent of iodine overload or to the occurrence of de novo thyroid autoantibodies. When a decreased thyrotropin (TSH) response to thyrotropin-releasing hormone occurred (in the absence of AIT), continuation of amiodarone medication was associated with a normalization of the TSH response in eight of 11 cases (73%); in contrast, an increased TSH response (in the absence of AIH) returned to normal in one of four cases (25%).

CONCLUSION

In euthyroid subjects living in an area with a moderately sufficient intake of iodine, there is a higher incidence of AIT than of AIH. AIH is an early event, occurring especially in women with thyroid autoantibodies prior to treatment. Cases of AIT continue to occur during amiodarone therapy; its development is unpredictable and of unexplained sudden onset. The value of regular thyroid function testing is therefore limited during amiodarone administration.