Neurogenic inflammation induced by capsaicin in patients with psoriasis.

Increasing doses of capsaicin were applied topically to the forearm skin of 30 patients with psoriasis, 16 patients with systemic scleroderma and 16 healthy volunteers. Only one-third of the patients with psoriasis responded with neurogenic inflammation to capsaicin doses of 0.125 and 0.25 microgram/cm2 in contrast to 81% of scleroderma patients and all the normal controls, who showed a positive cutaneous reaction. Higher doses of capsaicin (0.5-4 micrograms/cm2) were required to induce erythema and flare in patients with late-onset psoriasis (after 21 years of age) as well as in patients with more than 40% of skin surface involved with psoriatic lesion.