Profile of Hypothyroidism in Down's Syndrome

Objective: Although the association between Down's syndrome (DS) and thyroid dysfunction is well recognized, the cause of this condition is not known. Methods: Hospital records of patients with DS and hypothyroidism referred to our clinic were retrospectively reviewed. Initial thyroid hormone and thyrotropin (TSH) levels, age at admission, initial anthropometric measurements, age at the beginning of therapy, initial L-thyroxine (L-T4) doses, time to normalization of the thyroid function tests, and L-T4 dose at last visit were recorded. Thyroid ultrasound imaging was used to measure the size of the gland. Descriptive data were expressed as mean +/- SD values. Skewed data were shown as median and interquartile ranges (IQR). Results: There were 62 patients with DS (32 male and 30 female). Median TSH level at the first visit was 10.40 (19.4) mu IU/mL and median free T4 level was 1.18 (0.43) ng/dL. There was no statistical difference in terms of age, hormone and antibody levels, thyroid volume and L-T4 doses between boys and girls. Thyroid volumes of 54 patients were measured. Only nine of these patients had a normal-sized thyroid gland. Median total thyroid volume was 0.89 (2.07) mL. Thyroid volume was negatively correlated to L-T4 dose at last visit (p=0.006, r=-0.387). Conclusions: We found a high prevalence of thyroid dysgenesis in patients with DS and hypothyroidism. This association has not been reported before. Further studies investigating the thyroid gland size in these patients need to be performed to confirm the results.