COMPARATIVE SCREENING FOR THYROID-DISORDERS IN OLD-AGE IN AREAS OF IODINE DEFICIENCY, LONG-TERM IODINE PROPHYLAXIS AND ABUNDANT IODINE INTAKE

OBJECTIVE To investigate the effect of varying amounts of iodine intak e on the prevalence of thyroid dysfunction, autoimmunity and goitre in old age. DESIGN The first screening study where elderly subjects with varying amounts of iodine supply but from the same geographical and e thnographical region (Carpathian basin) were compared, and all hormone measurements and ultrasonography were performed by the same laborator y or person. PATIENTS Nursing home residents were screened for thyroid disorders from: (A) an iodine-deficient area, Northern Hungary (n=119 ; median age 81 years; median iodine excretion (MIE) 0.065 mu mol/ mmo l creatinine (equivalent to 72 mu g/g creatinine); (B) an area of obli gatory iodinated salt prophylaxis since the 1950s, Slovakia (n=135; me dian age 81 years, MIE 0.090 mu mol/mmol creatinine (equivalent to 100 mu g/g creatinine)) and (C) an abundant iodine intake area, Eastern H ungary (n=92; median age 78 years; MIE 0.462 mu mol/mmol creatinine (e quivalent to 513 mu g/g creatinine)). MEASUREMENTS TSH, T4, free T4, T 3, thyroglobulin (Tg), antibodies to Tg (AbTg) and to thyroid peroxida se (AbTPO), iodine excretion, ultrasonography of the thyroid gland. RE SULTS In regions A, B and C, the prevalence of unsuspected clinical hy pothyroidism was 0.8%, 1.5% and 7.6% (P=0.006), with all cases except one being antibody positive (Ab+). The occurrence of subclinical hypot hyroidism was 4.2% in region A, 10.4% in region a and 23.9% in region C (P<0.001), but only 3 of 22 cases with subclinical hypothyroidism fr om region C were Ab+. The overall prevalence of Ab positivity (either antiTg+ or antiTPO+) was similar in the three regions (A, 19.3%; B, 24 .4%; C, 22.8%). The occurrence of hyperthyroidism (clinical plus subcl inical) was 3.4% in region A, 3.0% in region B and 0% in region C (not significant). The rate of elevated Tg levels was similar in the three regions. The prevalence of goitre was 39.4%, 16.4% and 12.2% (P<0.001 ), respectively in regions A, B and C. In euthyroid subjects the mean ultrasonographically determined thyroid volume was 21.9 ml in region A , 13.6 ml in region B and 15.1 ml in region C (ANOVA F=5.76; P=0.0038) . There was no significant difference in the occurrence of cases with hypoechogenic echotexture of the thyroid gland. CONCLUSIONS The screen ing for hypothyroidism in nursing home residents living in iodine-rich regions is justified by the high prevalence of unsuspected clinical h ypothyroidism. The high prevalence of antibody positivity in old age i s independent of the iodine supply, but iodine supply has a determinin g role in the development of autoimmune hypothyroidism in the aged. Mo st cases of subclinical hypothyroidism in iodine-rich regions are not of autoimmune origin. In old age, hypoechogenic texture of the thyroid gland is not predictive of thyroid dysfunction.