Myxoedema and thyrotoxicosis: relations between clinical state and concentrations of thyroxine and triiodothyronine in blood

Hypothyroid Symptoms Fail to Predict Thyroid Insufficiency in Old People: A Population-Based Case-Control Study

BACKGROUND

Clinic-based studies have indicated that older hypothyroid patients may present only few symptoms.

METHODS

In this population-based study of hypothyroidism, we investigated how the power of symptom presence predicts overt hypothyroidism in both young and older subjects. We identified patients newly diagnosed with overt autoimmune hypothyroidism in a population (n = 140, median thyroid-stimulating hormone, 54.5; 95% confidence interval [CI], 28.3-94.8; median total T4, 37; 95% CI, 18-52) and individually matched each patient with 4 controls free of thyroid disease (n = 560). Participants filled out questionnaires concerning the presence and duration of symptoms. We compared the usefulness of hypothyroidism-associated symptoms in predicting overt hypothyroidism in different age groups (young: <50 years, middle age: 50-59 years, old: ≥60 years) also taking various confounders into account.

RESULTS

In young hypothyroid patients, all 13 hypothyroidism-associated symptoms studied were more prevalent than in their matched controls, whereas only 3 of those (tiredness, shortness of breath, and wheezing) were more prevalent in old patients. The mean numbers of symptoms presented at disease onset were 6.2, 5.0, and 3.6 at the ages of 0 to 49 years, 50 to 59 years, and 60+ years, respectively. In young versus old people with 0 to 1 symptoms, the odds ratio for being hypothyroid was 0.04 (95% CI, 0.007-0.18) versus 0.34 (95% CI, 0.15-0.78) (reference all other groups). In young versus old subjects reporting ≥4 symptoms, the odds ratio for being hypothyroid was 16.4 (95% CI, 6.96-40.0) versus 2.22 (95% CI, 1.001-4.90). Receiver operating characteristic analyses revealed that the symptom score was an excellent tool for predicting hypothyroidism in young men (area under the receiver operating characteristic curve, 0.91; 95% CI, 0.82-0.998), whereas it was poor in evaluating older women (area under the receiver operating characteristic curve, 0.64; 95% CI, 0.54-0.75).

CONCLUSION

Hypothyroid symptom score is a good discriminating tool to identify hypothyroidism in young patients but fails to identify hypothyroidism in the elderly. Thus, thyroid function should be tested on wide indications in old age.

Treatment of paediatric hyperthyroidism but not hypothyroidism has a significant effect on weight

OBJECTIVE

Thyroid hormones are involved in metabolic regulation, but the degree to which they affect body weight and body mass index (BMI) in children is unclear. We examined the effect of hypo- and hyperthyroidism on weight and BMI at the time of diagnosis and after appropriate treatment.

DESIGN

Prospective and retrospective case series.

PATIENTS

Children referred for thyroid dysfunction were enrolled prospectively if their total or free T4 was elevated with TSH <0·05 mIU/ml (N = 57) or if they had a subnormal total or free T4 and TSH >20 (N = 29).

RESULTS

Almost all patients had at least 2 classic signs or symptoms including goitre, but hyperthyroid patients had more symptoms. Mean BMI z scores at the time of diagnosis did not significantly differ between the two groups. Males with hyperthyroidism complained of weight loss more frequently and had a lower pretreatment BMI z score than hyperthyroid females. Hypothyroid patients lost a minimal amount of weight by the first follow-up (mean of 0·3 kg) and on average gained weight by the second follow-up visit. In contrast hyperthyroid patients gained a mean of 3·4 kg at the first follow-up visit and a mean of 7·1 kg by the second.

CONCLUSIONS

Correction of hypothyroidism resulted in minimal weight loss, suggesting that hypothyroidism does not cause significant weight gain in children. In contrast, correction of the hyperthyroid state had a somewhat greater impact on weight status. These results are consistent with prior reports but surprising given the opposite metabolic effects of hypo- and hyperthyroidism.

Serum TSH is positively associated with BMI

OBJECTIVE

To investigate whether there is an association between serum thyroid-stimulating hormone (TSH) within the normal range and body mass index (BMI).

DESIGN AND SUBJECTS

The study was performed in 6164 subjects (2813 males) who attended the fifth Tromsø study in 2001, and in 1867 subjects (873 males) that attended both the fourth Tromsø study in 1994/1995 as well as the fifth Tromsø study.

MEASUREMENTS

Height, weight, and serum TSH were measured in all subjects, and smoking status was recorded.

RESULTS

Smokers and nonsmokers were analyzed separately. In the fifth Tromsø study, serum TSH was positively and significantly associated with BMI in the nonsmokers. Within the normal TSH range (defined as the 2.5-97.5 percentile), nonsmoking males in the highest TSH quartile had a mean BMI 0.4 kg/m(2) higher compared to those in the lower quartile, whereas the difference for nonsmoking women was 1.4 kg/m(2). Similarly, in nonsmokers in the longitudinal study, there was a significant and positive association between delta serum TSH (serum TSH in 2001 minus serum TSH in 1994) and delta BMI in those with serum TSH within the normal range both in 1994 and 2001. In these subjects, the quartile with the highest delta serum TSH had a mean increase in BMI from 1994 to 2001 that was 0.3 kg/m(2) higher compared to those in the quartile with the lowest delta serum TSH. For the smokers, relations between serum TSH and BMI were not statistically significant.

CONCLUSION

In nonsmokers there is a positive association between serum TSH within the normal range and BMI.

Reversal of decreased hepatic lipase and lipoprotein lipase activities after treatment of hypothyroidism

Plasma lipoprotein concentrations, activities of hepatic lipase and lipoprotein lipase in post-heparin plasma, and the removal rate of exogenous triglyceride were measured in fourteen patients with severe primary hypothyroidism before and after 4 months substitution therapy with 1-thyroxine. Before treatment plasma LDL cholesterol concentrations were markedly increased while HDL cholesterol and plasma triglycerides were in the upper reference range. Thyroxine substitution led to a normalization of LDL cholesterol in all patients. Plasma triglycerides and HDL cholesterol decreased moderately. Hepatic lipase and lipoprotein lipase activities were initially reduced but increased significantly after treatment, by about 170% and 55%, respectively. The increase in hepatic lipase activities was significantly correlated to the increase in serum triiodothyronine levels and also to the reduction in LDL cholesterol concentrations. The decrease in LDL cholesterol was also significantly correlated to the increase in serum triiodothyronine concentration. In two patients initially treated with triiodothyronine, the activity of hepatic lipase, but not that of lipoprotein lipase, increased after 24 and 48 h, while LDL cholesterol levels decreased substantially. We suggest that the reduced activities of hepatic lipase as well as of lipoprotein lipase are important pathogenetic factors for the dyslipoproteinaemia occurring in hypothyroidism and that the low serum triiodothyronine concentration is of major importance for the alterations in lipid transport.

Effect of experimental thyrotoxicosis on oxidative phosphorylation in rat liver, kidney and brain mitochondria

Coupled phosphorylation was examined in liver, kidney and brain mitochondria from rats made thyrotoxic by injecting repeated doses of triiodothyronine. Liver and kidney mitochondria were maximally affected under these conditions, whereas effects on brain mitochondria were marginal. State-3 respiration rates with succinate decreased considerably in all the tissues, whereas glutamate oxidation increased in liver, but decreased in kidney and brain mitochondria. Oxidation rates of beta-hydroxybutyrate decreased in kidney and brain mitochondria but were not significantly affected in liver mitochondria. Oxidation of ascorbate + TMPD was not affected. State-4 respiration rates increased in general with all the substrates resulting in lowering of the RCI. The ADP/O ratios decreased in a site-specific manner in the mitochondria from the three tissues. The content of cytochrome b decreased in all three tissues, whereas the content of cytochrome c + c1 increased in liver and kidney but decreased in brain. The content of cytochrome a, however, was not significantly affected. Basal and Mg2+-stimulated ATPase activities increased in mitochondria of liver and kidney but not in those of brain; total ATPase activities, however, were not altered. The results imply that excessive levels of thyroid hormones over normal in the serum can lead to impairment of mitochondrial energy metabolism in a tissue-specific manner.