RECOGNITION OF A SUBGROUP OF ADOLESCENTS WITH RAPIDLY GROWING THYROIDS UNDER IODINE-REPLETE CONDITIONS - 7 YEAR FOLLOW-UP

Objective: To evaluate whether small iodine supplements decrease the i ncidence of adolescent thyroid hypertrophy in an iodine-sufficient pop ulation or whether such thyroid enlargement should be considered an in evitable physiological phenomenon. Design: Beginning in September 1991 (after an initial examination in September 1990), 54 11-year-old chil dren in Bardejov, Slovakia were given small iodine supplements (Thyroj od depot tablets containing 1530 mu g iodide) every 2 weeks for 2 year s followed by once weekly for 2 years. A second group of 63 children s erved as controls. In June 1995, there were still 52 treated and 60 co ntrol children in the study and these were examined; 44 treated and 48 control children remained in the study until June 1997. Methods: In 1 990, 1993, 1995, 1996 and 1997 the thyroid volume (ThV) was measured b y ultrasound. Serum levels of TSH, thyroglobulin, total and free thyro xine and tri-iodothyronine and anti-thyroid peroxidase (anti-TPO), ant i-thyroglobulin (anti-TG) and anti-TSH receptor (TSR) antibodies were estimated in 1990 and 1994, while only TSH, and anti-TPO and anti-TSR antibodies were measured in 1997. Results: There was no difference bet ween the groups at any interval in the serum levels of the hormones me asured. Marginally increased TSH was found in two treated and two cont rol children. Anti-TSR antibodies were negative in all children, while anti-TPO and anti-TG antibodies were found in one treated and four co ntrol children. At the age of 10 years (1990), 84% of all ThVs were le ss than 4 ml, indicating a previous life-long sufficient iodine intake . After the treatment was completed (June 1995), a significant differe nce in ThV (P < 0.04) was found between the whole treated (5.78 +/- 0. 19 ml) and the whole control group (6.56 +/- 0.30 ml), However, there was already a marked difference in the 75th percentile (6.4 ml in trea ted vs 8.5 ml in controls) due to more rapid thyroid growth in certain children of the control group (ThV >7.0 ml in 6/52 treated children v s 24/60 controls: P < 0.01). Since such differences were much higher i n 1997, the children in each group whose ThV was in the range of the u pper 25% in 1997 were retrospectively evaluated as arbitrary separate subgroups in all the time intervals and compared with the remaining 75 % of children who showed moderate thyroid growth rate, Two years after the termination of treatment (June 1997), excessive thyroid growth co ntinued in the upper quarter of 12 controls with the highest ThV (13.6 0 +/- 0.40 ml or 7.60 +/- 0.29 ml/m(2); 12/12 with ThV >11.0 ml), and a similar subgroup now also appeared in 11 previously treated children (10.79 +/- 0.51 ml or 6.19 +/- 0.30 ml/m(2); 5/11 with ThV >11.0 ml), At the same time, ThV in the remaining 75% of both control (8,12 +/- 0.38 ml or 4.82 +/- 0.17 ml/m(2); 3/36 with ThV >11.0 ml) and treated (7.20 +/- 0.30 ml or 4.39 +/- 0.17 ml/m(2); 0/33 with ThV >11.0 ml) ch ildren was significantly less (P < 0.01 to P < 0.001) than that in the appropriate rapidly growing subgroups. During the whole observation p eriod (1990-1997), no difference was found between treated and control subgroups with moderate thyroid growth. Conclusions: Since iodine int ake in Slovakia has been adequate for decades and sporadic iodine defi ciency is highly unlikely, the observed excessive thyroid growth in ce rtain adolescents may result from causes other than simple iodine defi ciency (e.g. hereditary), which are nevertheless ameliorated by small iodine supplements. The question remains whether such a subgroup with rapidly growing thyroids should be included in the range of normal thy roid volumes in adolescents.