Lichen amyloidosis (LA) is an itchy skin disorder characterized by amyloid deposits in the superficial dermis. We evaluated in detail the sensitivity against tactile stimulation in the skin, especially the hyperkeratotic papule and its edge, of LA patients. Six LA patients with pruritus and five healthy subjects were tested. Evaluation of the skin’s sensory sensitivity through the application of a non-noxious mechanical stimulus on the skin and hyperkeratotic papules with a von Frey filament (vFF, 0.69 mN strength) showed that there was no difference in the sensory sensitivity of the skin of healthy subjects and the healthy region of LA patients. In the center of the hyperkeratotic papules, the patients’ response against vFF was low. However, when the edge of the hyperkeratotic papule was stimulated with vFF, the LA patients responded highly. In addition, the LA patients also responded against the stimulation of the periphery of the hyperkeratotic papule with vFF (P = 0.0784). These results suggest that an increase in sensory sensitivity around the hyperkeratotic papules, including their edges, may be involved in the induction of pruritus. In the histopathological study, we demonstrated that the sensory sensitivity at the edge, but not center, of hyperkeratotic papules in LA patients was increased through the epidermal elongation of peripheral sensory neurons. Moreover, we also found the increase of the expression of 5-lipoxygenase, which was involved in the pruritogen LTB4 production, at the edge of hyperkeratotic papules, suggesting that at least LTB4, which activates directly primary afferents, is a pruritogen in LA patients.

Increase in sensory sensitivity around the hyperkeratotic papule may be involved in pruritus in lichen amyloidosis