Eosinophilia-myalgia syndrome (L-tryptophan-associated neuromyopathy). Histopathologic study of skeletal muscle biopsy in a patient with eosinophilia-myalgia syndrome following L-tryptophan use showed prominent lymphocytic perineuritis, neuritis, and perimysial fasciitis. The presence of perineuritis and neuritis provides a histopathologic basis for clinical features of neuropathy in eosinophilia-myalgia syndrome and occurred in conjunction with a fasciitis or interstitial myositis that was predominantly perimysial and focally endomysial. 