Prevalence of Autoimmune Thyroiditis in School Children 10 Years After Normalized Iodine Intake

Iodine deficiency has been identified as a significant public health problem in Iran. The main strategy for control of iodine deficiency was country wide salt iodination. 10 years after starting this program, goiter is still endemic in some school children. The most important differential diagnosis is autoimmune thyroiditis. The aim of the present study was to evaluate prevalence of autoimmune thyroiditis in school children with normalized iodine intake. 1188 school children, aged 8-13 years, were selected by cluster random sampling to evaluate prevalence of goiter. From a total of 1188, 500 school children were chosen to assess urinary iodine excretion, free T4, free T3, TPO anti body (TPOAb) and TSH. Goiter was endemic in 39.6 %(95% CI 36/3%-41/7%) but majority of them had grade I thyromegaly. Median urinary iodine excretion (18/8 µg/ dl) indicated normal iodine intake. Mean (95%CI) free T4, free T3 and TSH concentration were 13.1(12.8-13.3) pg/ml, 3.7(3.6-3.8)pg/ml and 2.5 (2.2-2.8) IU/ml respectively. TPOAb was positive in 3.7% of children with a higher prevalence in girls(P< 0.001). The prevalence of hypothyroidism and hyperthyroidism was 9% and 0.2% respectively but only 0.8% of school children had TSH>10. There was a significant relationship between detection of positive TPOAb, prevalence of goiter and hypothyroidism however no relation was seen between urinary iodine excretion status and detection of positive TPOAb, hypothyroidism and prevalence of goiter. Despite median urinary iodine excretion being normal, persistence of goiter suggested presence of goiterous factors alhought the autoimmune mechanisms of thyroid may to some extent autoimmune of thyroid explain some part of the goiter prevalence it is however necessary to evaluate other factors.