Histamine and cutaneous nociception: histamine-induced responses in patients with atopic eczema, psoriasis and urticaria.

Having observed altered itch and flare reactions after histamine application in patients with atopic eczema, we tried to determine these reactions in patients with urticaria and psoriasis. We investigated 16 healthy non-atopic subjects, 16 atopics in an eczema-free interval, 16 with acute atopic eczema, 16 with urticaria and 16 with psoriasis. Histamine was iontophoretically applied. The resulting sensations were rated on a visual analogue scale. Flare areas were measured 6 min after stimulation. Itch ratings of urticaria and psoriasis patients did not differ significantly from controls, whereas both atopic groups, regardless of acute or symptom-free state, reported significantly reduced intensity of itching. Flares were significantly diminished in all subjects with acute skin disease (psoriasis, urticaria and atopic eczema), regardless of diagnosis. However, flares were "normal" in symptom-free atopics and were not significantly different from controls. In conclusion, all "acute" patients showed a diminished axon-reflex function, possibly due to a downregulation of C-fiber responsiveness to histamine or an increased turnover rate of inflammatory mediators. Both atopic groups reported weaker itching, suggesting altered central nervous processing of itch.