Etiology, diagnosis, and treatment recommendations for central hypothyroidism associated with bexarotene therapy for cutaneous T-cell lymphoma.

Bexarotene is a synthetic retinoid X receptor (RXR)-selective retinoid recently approved for treatment of cutaneous T-cell lymphoma. In clinical trials, bexarotene was found to cause severe central hypothyroidism with high frequency, associated with marked reductions in serum concentrations of thyroid-stimulating hormone (TSH) and thyroxine. Further investigation demonstrated a novel mechanism causing this effect, namely reversible, RXR-mediated, thyroid hormone-independent suppression of TSH gene expression. Treatment of patients with bexarotene-induced hypothyroidism commonly requires high doses of thyroid hormone for replacement therapy, often twice the typical doses used to treat more common etiologies of hypothyroidism. These observations suggest that bexarotene probably has two fundamental effects on thyroid function: to suppress TSH production and to increase thyroid hormone metabolic clearance. Recommendations are provided for diagnosis and treatment of this syndrome.