Topical capsaicin in dermatologic and peripheral pain disorders.

Topical capsaicin has been introduced in the U.S. and Canada as a cream indicated for temporary relief of neuralgia following episodes of herpes zoster infections and in the treatment of diabetic neuropathy. Although capsaicin is clinically used as an external analgesic for temporary relief of neuralgia, it has also been widely used as a research tool to study peripheral pain. Capsaicin apparently works to release substance P from sensory nerve fibers and after repeated applications, depletes neurons of substance P. Clinical investigations of topical capsaicin include trials in chronic pain syndromes such as postherpetic neuralgia, postmastectomy neuroma, reflex sympathetic dystrophy syndrome, diabetic neuropathy, rheumatoid arthritis, psoriasis, hemodialysis-associated itching, and vulvar vestibulitis. In addition, therapeutic benefits of capsaicin cream on apocrine chromhidrosis have been described. Further clinical studies are warranted in several of these conditions to establish the efficacy of topical capsaicin. Serious or unexpected adverse reactions from clinical use have not been reported to date. Considering the paucity of safe and effective treatments for the conditions mentioned above, capsaicin cream appears to warrant further clinical investigations to establish its efficacy in a variety of chronic pain syndromes.