Bone density is not reduced during the short-term administration of levothyroxine to postmenopausal women with subclinical hypothyroidism: a randomized, prospective study.

PURPOSE: Controversy exists as to whether patients with subclinical hypothyroidism benefit from treatment. Two randomized trials reported that hypothyroid symptoms improved following thyroid hormone replacement therapy. However, during the initial treatment of overt hypothyroidism with levothyroxine, three studies have demonstrated short-term (6 to 12 months) 5% to 13% reductions in bone density. The current study measures bone density during the initial treatment of subclinical hypothyroidism.

PATIENTS: Seventeen postmenopausal women with subclinical hypothyroidism (elevated serum thyrotropin [TSH] and normal serum free thyroxine concentrations) and no prior history of thyroid disease were randomly assigned to levothyroxine treatment or no treatment and followed prospectively. Patients in the treatment group had similar initial serum TSH concentrations (9.8 +/- 3.3 versus 8.4 +/- 2.7 microU/mL) but were slightly older (68 +/- 7 years versus 60 +/- 5 years [p < 0.02]). The average dose of levothyroxine needed to normalize serum TSH concentration was 0.072 +/- 0.027 mg.

RESULTS: Bone density determinations were not significantly different between the two groups at baseline. After 14 +/- 1 months, single-photon absorptiometry of the wrist decreased by 1.8% +/- 3.2% in the untreated patients and 0.5% +/- 4.1% in the levothyroxine-treated patients (p = NS). Dual-energy X-ray absorptiometry of the lumbar spine decreased by 0.7% +/- 2.9% in the untreated patients and rose 0.1% +/- 4.75% in the levothyroxine-treated patients (p = NS).

CONCLUSIONS: Unlike the early treatment of overt hypothyroidism, there is no short-term reduction of bone density with levothyroxine treatment of subclinical hypothyroidism in postmenopausal women. These data suggest that potentially symptomatic women with subclinical hypothyroidism should be given a trial of levothyroxine therapy without concern about adverse effects on skeletal integrity.