CLINICAL STUDY Evolution of thyroid autoimmunity during iodine prophylaxis – the Sri Lankan experience

Objective: To study the evolution of thyroid autoimmunity, in relation to the change in goitre prevalence, during 3 years of iodine prophylaxis in Sri Lanka. Methods: Two groups of Sri Lankan schoolgirls between the ages of 10.8 and 17.5 years were studied in 1998 (401 girls) and 2001 (282 girls). A prospective study was performed in 42 schoolgirls who were thyroid autoantibody (Ab)-positive (þve) in 1998. Anthropometric measures, urinary iodine excretion (UIE), thyroid volume, free thyroxine, free tri-iodothyronine, TSH, and thyroglobulin (Tg) and thyroid peroxidase (TPO) Ab were evaluated in all 683 girls. Results: Goitre prevalence was significantly lower in 2001 compared with 1998 related to age (2.9% compared with 20.2%) and body surface area (11.6 % compared with 40.8%), although UIE was unchanged. Prevalence of thyroid Ab in 2001 was also lower (23.4 % compared with 49.9%); among those with the Ab, 34.8 % had TgAb alone and 46.9 % had a combination of TgAbþTPOAb, compared with 82.0 % TgAb alone in 1998. In 2001, subclinical hypothyroidism was more frequent in Abþve (6.3%) than Ab-negative girls (1.0%). A cohort of 42 Abþve schoolgirls in 1998 (34 with TgAb alone, eight with TgAb þ TPOAb) were evaluated again in 2001. Only 10 of them (23.8%