Itch and atopic dermatitis: clinical and experimental studies

The aims of the study were to develop and evaluate methods for quantitative measurement of itch, to investigate the perception of itch in patients with atopic dermatitis (AD), and to measure itch in such patients during treatment with H1-receptor antagonists or cyclosporin A, thereby exploring possible mechanisms in the pathogenesis of itch in AD. In a double-blind, randomized, placebo-controlled, cross-over study of 30 AD patients using a potent, topical, antipruritic corticosteroid, two methods for measuring itch both successfully detected the itch-relieving effect of the corticosteroid. The two methods comprised new portable data-loggers (Pain-Track) for continuous recording of itch, and conventional visual analogue scale (VAS) forms for retrospective recording. The main advantages of the Pain-Track method are possibilities for frequent sampling, surveillance of compliance, and analysis of a large amount of data. Induction and measurement of experimental histamine-induced itch were studied in 38 healthy subjects. It was shown that pruritic stimuli should be presented in a random order so as to avoid systematic errors in the perception of itch. Two rating scales, a seven-stepped non-verbal scale on a Pain-Track logger, and a 100-mm VAS on a potentiometer, were found valid for continuous recording of itch. The perception of experimental itch was studied in 32 AD patients and 32 healthy controls. The itch responses provoked by wool fibres were significantly stronger in AD patients than in controls, whereas the histamine-induced dose-response curves for itch did not differ significantly between the two groups, who discriminated equally well between weak and strong histamine stimuli. No increased skin mast cell releasability was shown in vivo to compound 48/80 in AD patients. Their itch responses to the different pruritic stimuli did not correlate with clinical itch intensity, eczema score or serum IgE-level. In a double-blind, randomized, placebo-controlled, cross-over study of 25 AD patients, the effect on clinical itch of a sedative (clemastine) and of a non-sedative (terfenadine) antihistamine did not differ from that of placebo, although both drugs had a pronounced H1-receptor-antagonizing effect in the skin and clemastine was significantly sedative. These findings support the view that histamine is not the major pruritogen in AD, and that sedation is not necessarily associated with itch relief. In a double-blind, randomized, placebo-controlled, cross-over study of 10 AD patients, 10 days' treatment with cyclosporin A (CSA), 5 mg/kg/day, significantly reduced itch intensity, eczema score and the number of peripheral blood eosinophils.