Subclinical hypothyroidism associated with the positive perchlorate discharge test in aged subjects (author's transl)

Abstract

To investigate the prevalence and characteristics of subclinical hypothyroidism in aged subjects, determinations of plasma TSH levels were made in 172 patients (54 males and 118 females) over the age of 55, who were examined in the out-patient clinic. Although they had one of the clinical signs of hypothyroidism such as a puffy face, dry skin, general malaise, cold intolerance, constipation, hypercholesteremia and elevated serum LDH level, they had no other clinical picture of overt hypothyroidism. Their underlying lesions were hypertension, cardiac diseases, cerebrovascular diseases, chronic obstructive lung disease, mild diabetes mellitus (type II) and mild liver diseases. All the patients were apparently in a normal nutritional state without any specific medications which could cause thyroid abnormalities. Patients with overt thyroid diseases or severe illness were not included in the present study. In addition, the occurrence of anti-thyroid antibodies were also investigated in sera from 112 of 172 patients, using the thyroglobulin-coated and microsome-coated tanned red cell hemaglutination tests.Seventeen (6 males and 11 females) subjects, aged 58 to 83, had elevated plasma TSH levels, ranging from 12.1μU/ml to 170μU/ml. Although the incidence of circulating thyroid antibodies in 112 patients examined was apparently higher (5.7% in men and 19.5% in women) than that reported previously in control subjects, 15 of 17 patients with elevated TSH levels had no detectable thyroid antibodies in repeated determinations. Previous reports have suggested that latent thyroid failure detected in aged subjects might be mainly due to Hashimoto's thyroiditis. However, the present findings suggest the existence of other factor (s) as a cause of subclinical hypothyroidism in aged subjects.Since 16 of 17 patients with elevated TSH levels had elevated 99mTc thyroid uptake, ranging from 2.5% to 12.9%, the perchlorate discharge test was performed 6 hours after the administration of 123I. In 15 of 17 cases, 123I thyroid uptake was markedly diminished immediately after the administration of 1 g perchlorate, and the discharge rates ranged from 27% to 88% (mean ± SE = 67 ± 5%). Moreover, 13 of 15 patients with positive perchlorate discharge test had markedly diminished T4 levels in serum (mean ± SE = 2.7 ± 0.5μ/dl in 15 patients), and 13 patients had almost normal T3 levels (mean ± SE = 107 ± 8ng/dl in 15 patients), indicating “T3-euthyroidism” in these patients. On the other hand, 2 patients with negative perchlorate discharge tests showed completely normal T4 and T3 levels in serum. Four patients had a very small goiter detected only by careful palpation, and the remaining 13 patients had no detectable goiters even in CT scan examination. Furthermore, the histological features of Hashimoto's thyroiditis were not found in the thyroid biopsy specimens obtained from 2 patients with a positive perchlorate discharge test.The present findings suggest that in aged subjects there exists subclinical hypothyroidism attributable to defective iodination in the thyroid, which is caused by some factor other than Hashimoto's thyroiditis. Whether or not the iodination defects in the thyroid arise from aging remains to be determined by future investigation.