Acetylcholine induces different cutaneous sensations in atopic and non-atopic subjects

The mediators eliciting pruritus in atopic eczema are a matter of discussion, since several substances may be involved and histamine is unlikely to be the main agent. Hence, in this study we examined the cutaneous sensations and vascular reactions in 15 patients with atopic eczema and in 15 non-atopic subjects after i.c. injection of acetylcholine (Ach, 0,5 M, 20 microliter) or buffered saline, respectively. The sensory perceptions were rated by a visual analogue scale (VAS) as to quality and intensity, and the vascular reactions were monitored by laser Doppler flowmetry and evaluated planimetrically as to flare and wheal extension. The flares and wheals in both groups were similar; yet the cutaneous sensations significantly differed, since all patients with atopic eczema complained of "pure" itching after Ach-injection, whereas the controls reported a burning pain. The patients with atopic eczema started their ratings significantly earlier and rated significantly longer than the controls. Our results provide evidence that Ach may play an important role in the etiology of pruritus in atopic eczema patients.