Patients' perception of itch induced by histamine, compound 48/80 and wool fibres in atopic dermatitis

Itch and flare responses were investigated in 32 patients with atopic dermatitis (AD) and in 32 healthy controls. Itch was induced chemically by intradermal injections of histamine (1, 3.3, 10 and 100 micrograms/ml) and compound 48/80 (10 micrograms/ml) into non-lesional skin and mechanically by wearing a woollen sweater. Continuous recording of itch intensity allowed the calculation of itch duration (ID), maximal itch intensity (Imax) and a "total itch index" (Tii). The itch responses were significantly increased in AD patients compared with controls for wool fibres and one of the histamine concentrations (10 micrograms/ml), but not for the remaining three histamine concentrations or compound 48/80. Conversely, the flare response was significantly smaller in AD patients than in controls for the two strongest histamine solutions and compound 48/80. Significant dose-response relationships were found between histamine concentration and each of ID, Imax, Tii and flare in both patients and controls. The slope of the flare-regression line was significantly steeper in controls than in AD patients, whereas the slopes of the itch-regression lines did not differ significantly between the two groups, i.e. their ability to discriminate between weak and strong histamine concentrations did not differ significantly. No increased skin mast cell releasability in vivo to compound 48/80 was shown in AD patients compared with controls. The itch and flare responses of AD patients did not correlate significantly with clinical itch intensity, eczema score or serum IgE level.