ABSTRACT

Aim: Although subnormal TSH between 0.1-0.4 mIU/L is fairly common and benign, suppression of TSH to < 0.1mIU/L with normal free T4 is less common and more worrisome. We have conducted a retrospective chart review of a collection of such cases and have summarized the features and outcome on follow up.

Methods: We studied 23 consecutive patients referred from 2005-07 to our pediatric endocrine clinic with TSH < 0.1 mIU/L and free T4 in the range of 0.8-2 ng/dl. We collected historical, clinical and laboratory data, and analyzed their outcome.

Results: The natural evolutions of these subjects were separated into 4 groups. Group 1, 14 subjects, (61%) became euthyroid within a mean of 3.7 months. Group 2, 4 subjects, (17%) became hypothyroid within a mean of 2.8 months. Group 3, 2 subjects (9%) progressed to overt hyperthyroidism. Group 4, 3 subjects (13%) had persistently suppressed TSH, 8-14 months after initial testing, of which one had a multinodular goiter and had a thyroidectomy. Elevated thyroid peroxidase antibody (TPO) was seen in 54.5% of those tested.

Conclusion: Only 2/23 in our series became overtly hyperthyroid. Substantial number of subjects had a short period of transient TSH suppression that resolved spontaneously. Markers suggestive of autoimmune thyroid disease were consistently seen in group 2 and less so in others. It is prudent to observe such cases in the short term with serial follow up TSH, free T4 and T3, and to reserve further testing and treatment for those who become symptomatic or do not resolve.