Histamine and Cutaneous Nociception: Histamine-Induced Responses in Patients with Atopic Eczema;Psoriasis and Urticaria.

Abstract

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.