Spontaneous normalization of thyrotropin concentrations in patients with subclinical hypothyroidism

Patients with subclinical hypothyroidism may revert to normal TSH values.

The objective of this study was to examine the time course of the normalization of TSH levels in subclinical hypothyroidism.

This was a prospective, observational study with no intervention, with a duration of follow-up of 12-72 months.

Outpatients visited an endocrinology clinic of a general hospital.

Forty patients (32 women, mean age 62.8 +/- 8.2 yr) with spontaneous subclinical hypothyroidism (TSH > 5 mU/liter and normal free T(4)) participated in the study. Each patient normalized their TSH values without T(4) therapy throughout the follow-up.

TSH and free T(4) levels were evaluated every 6 months.

Normalization occurred at a median time of 18 months (range, 6-60 months). Fifteen patients normalized their TSH levels during the first year of follow-up and 27 during the first 2 yr. Ten patients normalized their TSH values at the fourth or fifth year. Only four patients reverted to TSH values less than 2 mU/liter. Final TSH levels achieved by the patients were significantly correlated with the time elapsed until normalizing these levels (r = 0.367; P = 0.020).

There is no clear pattern of TSH normalization, although most patients normalize their TSH values early in the follow-up. The final TSH reached seems to be related to the time of normalization.