Subclinical Hypothyroidism: A Prospective Observational Study from Southern India

Objective: To assess the natural history and progression of subclinical hypothyroidism and to study factors which help predict evolution of subclinical hypothyroidism into overt hypothyroidism.

Methods: Longitudinal study in 40 children (2-16 yrs) presenting with subclinical hypothyroidism in a tertiary care unit in Chennai, India. Patients showing evidence of overt hypothyroidism or thyroid stimulating hormone ≥15 mIU/mL during follow-up were started on thyroxine. Others were followed up with 3-monthly thyroid function tests up to one year.

Results: At the end of our study period 3 (7.5%) were overtly hypothyroid, 16 (40%) remained as subclinical hypothyroid, and 21 (52.5%) became euthyroid. Evidence of auto- immunity at baseline was a significant (P<0.05) risk factor for progression to overt hypothyroidism.

Conclusion: Subclinical hypothyroidism in children, with thyroid stimulating hormone upto 15 mIU/L and irrespective of thyroid autoimmunity, needs only periodic clinical and biochemical follow up. Thyroid autoimmunity may point to an increased probability of progression to overt hypothyroidism.