Selenium and the thyroid.

PURPOSE OF REVIEW: To provide information on the role of the essential trace element selenium, which enables appropriate thyroid hormone synthesis, secretion, and metabolism, and to discuss supplementation with various selenium compounds, which prevent thyroid diseases such as goiter and exert beneficial effects in thyroid autoimmune diseases. RECENT FINDINGS: Selenium administration in both autoimmune thyroiditis (M. Hashimoto) and mild Graves' disease improves clinical scores and well-being of patients and reduces autoimmune antibody titres in several prospective, placebo-controlled supplementation studies. SUMMARY: Adequate nutritional supply of selenium, together with the two other essential trace elements iodine and iron, is required for a healthy thyroid during development and adolescence, as well as in the adult and aging populations.

Weight loss after therapy of hypothyroidism is mainly caused by excretion of excess body water associated with myxoedema.

CONTEXT: In hypothyroidism, resting energy expenditure (REE) is reduced and weight gain is common. Physical activity contributes to the total daily energy expenditure, and changes in physical activity might contribute to hypothyroid-associated weight changes. OBJECTIVE: The objective of the present study was to evaluate mechanisms involved in body weight changes associated with hypothyroidism. DESIGN, SETTING, AND PARTICIPANTS: We conducted a 1-yr controlled follow-up study on outpatients newly diagnosed with hypothyroidism (n = 12) and a euthyroid measurement control group (n = 10). MAIN OUTCOME AND INTERVENTIONS: Changes in body mass and composition (dual-energy x-ray analysis scan), REE (indirect calorimetry), and spontaneous physical activity (pedometers and two different questionnaires) were studied before and after 12 months of L-T(4) therapy or observation (control group). RESULTS: TSH changed from 102 (85) to 2.2 (2.1) mU/liter mean (SD) and free T(4) from 4.5 (2.1) to 18 (3.3) pmol/liter after 1 yr of treatment. Body weight decreased from 83.7 (16.4) to 79.4 (16.0) kg (P = 0.002) due to change in the lean mass subcompartment only (P = 0.001) because fat and bone mass was virtually unchanged. Significant increase was observed in REE and in physical activity measured with questionnaires but not measured as daily steps. No significant changes were observed in the control group. CONCLUSION: L-T(4) therapy of hypothyroidism associated with significant decrease in body weight and increase in REE. Physical activity measured with questionnaires increased significantly, but not number of daily steps. Despite changes in REE and body weight, fat mass was unchanged during the study. We propose that total body energy equilibrium is maintained during treatment of hypothyroidism and that weight loss observed during such treatment is caused by excretion of excess body water associated with untreated myxoedema.

Hypothyroidism and myxedema coma.

Hypothyroidism is a common endocrinopathy in dogs but is rare in cats. Lymphocytic thyroiditis and idiopathic thyroid atrophy are common causes of this condition. Specific thyroid function tests, in conjunction with clinical signs and physical examination findings, are used to help confirm a diagnosis of hypothyroidism. This disease can be managed with synthetic hormone supplementation and has an excellent prognosis. Myxedema coma is a rare and potentially fatal manifestation of severe hypothyroidism that can be successfully treated using intravenous levothyroxine.

Um caso de liquen mixedematoso e cancro da mama / A case of lichen myxedematosus breast carcinoma

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Effects of selenium deficiency on thyroid necrosis, fibrosis and proliferation: a possible role in myxoedematous cretinism.

It has been suggested that selenium deficiency is a co-factor to iodine deficiency in the pathogenesis of myxoedematous cretinism. The mechanism proposed is that the generation of hydrogen peroxide is greatly increased in iodine-deficient thyroid glands, and that selenium is involved in the control of hydrogen peroxide and its derived free radicals. This study was carried out to investigate the effect of the possibly impaired cellular defence mechanism associated with selenium deficiency on thyroid necrosis and tissue repair. For this purpose, we studied thyroid tissue from selenium- (SE-) and/or iodine-deficient (I-) rats before and after an acute toxic iodine overload. In I- thyroids, necrotic cells were numerous. Acute iodine administration increased this effect. Necrosis was associated with transient infiltration of inflammatory cells. In I-SE+ thyroids the tissue resumed its normal appearance. In I-SE- thyroid glands, the iodide toxicity was stronger, with greater necrosis and inflammatory reaction. The inflammation resolved but was replaced by fibrotic tissue. Fifteen days after the toxic overload, the connective tissue volume was twice the control value. Before iodide overload, the proportion of dividing cells was equal in I-SE+ and I-SE- thyroids. Three days after the iodide overload, this proportion was increased in I-SE+ thyroids but reduced in the I-SE- thyroids. Overall, the I-SE- thyroids had four times fewer dividing cells than the I-SE+ thyroids. In summary, selenium deficiency coupled to iodine deficiency increased necrosis, induced fibrosis and impeded compensatory epithelial cell proliferation. These results are compatible with histological and functional description of thyroid tissue from myxoedematous cretins.

Selenium deficiency as a possible factor in the pathogenesis of myxoedematous endemic cretinism.

Myxoedematous endemic cretinism is prevalent in African goitre endemies. It has been related to a thyroid 'exhaustion' atrophy occurring near birth. It is proposed that this might result from the low resistance of a fragile tissue to enhanced H2O2 generation under intense thyroid stimulation by thyrotropin. In support of this hypothesis, low selenium and glutathione peroxidase serum levels have been found in the African endemic area of the Idjwi Island (Kivu, Zaire). Serum selenium and plasma glutathione peroxidase were lower in the area of high endemicity of goitre and cretinism (Northern part of the Island). However, only the former difference is statistically significant. These data thus suggest a role of oligoelements and oxygen toxicity in the pathogenesis of endemic cretinism.

[Endocrine aspects of Steinert's disease]. / Aspects endocriniens de la maladie de Steinert

The authors report a case of Steinert's disease in a woman and discuss the endocrine profile of this disease after giving an account of the criteria of diagnosis. Disorders of gonad function are mild in women, primary testicular atrophy is very frequent in man with reduction in 17-ketosteroids and testosterone. Thyroid function was normal but, in a few cases, a low fixation curve was found (our case) corrected by TSH stimulation. The frequency of cataract emphasizes the interest of this sign for detection. Diabetes, associated with hyperinsulinism, seemed more frequent than in a population without Steinert's disease. The pathogenesis of these endocrine disorders appears secondary and is ill explained if one considers it as a single disease. Better knowledge, no doubt linked to progress in biochemistry of normal and myopathic muscle, will help to explain the pathogenesis.