Increased muscle tone during etretinate therapy.

A 40-year-old man with severe psoriasis developed painless muscle stiffness coinciding with four successive courses of etretinate therapy. Peripheral nerve block extinguished the increased muscle tone. Our patient's symptoms resembled those of the stiff-man syndrome. Increased muscle tone is a potential side effect of etretinate treatment and must be distinguished from the common musculoskeletal symptoms observed in patients taking retinoid therapy.