Context: Patients with subclinical hypothyroidism may revert to normal TSH values.
Objective: The objective of this study was to examine the time course of the normalization of TSH levels in subclinical hypothyroidism.
Design: This was a prospective, observational study with no intervention, with a duration of follow-up of 12-72 months.
Setting: Outpatients visited an endocrinology clinic of a general hospital.
Patients: 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.
Measurements: TSH and free T(4) levels were evaluated every 6 months.
Results: 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).
Conclusions: 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.