Pentazocine-induced fibrous myopathy and localized neuropathy.

A 47 year-old woman who had a 4-year history of intramuscular pentazocine injections in the lower extremities, developed gradual stiffness and weakness of the lower extremities. The thigh and buttock muscles were "wooden-hard" on palpation. The skin was hard, shiny and hairless. Associated clinical and electrophysiological polyradiculopathy and multiple mononeuropathy of the lower extremities were observed. Imaging studies showed calcification and fibrosis of the involved muscles. Muscle biopsy revealed fibrous myopathy. Caution in longterm usage and early recognition of pentazocine toxicity as a neuromuscular complication are important in order to prevent irreversible drug-induced fibrous myopathy and localized neuropathy.