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Spontaneous Normalization of Thyrotropin Concentrations in Patients with Subclinical Hypothyroidism

Department of Endocrinology (J.J.D.), Hospital Ramón y Cajal, 28034 Madrid, Spain; Department of Endocrinology (P.I.), Hospital General, 40002 Segovia, Spain; and Endocrine Section (K.D.B.), Washington Hospital Center, Washington, D.C. 20010

Address all correspondence and requests for reprints to: Juan J. Díez, Department of Endocrinology, Hospital Ramón y Cajal, Carretera Colmenar km 9, 28034 Madrid, Spain. E-mail: mibarsd{at}infomed.es.

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 T₄) participated in the study. Each patient normalized their TSH values without T₄ therapy throughout the follow-up.

Measurements: TSH and free T₄ 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.

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