Pemphigus is an autoimmune blistering disorder with four major subtypes: pemphigus vulgaris (PV), pemphigus vegetans (PVe), pemphigus foliaceus (PF), and pemphigus herpetiformis (PH). Among them, PF and PH present itching as a clinical feature; however, the mechanisms behind the pruritus are still unclear. In this report, we sought to investigate the expression of a type 2 inflammation‐related pruritogenic cytokine IL‐31 and its receptor subunit IL‐31RA through immunofluorescence staining analysis. The number of eosinophils, basophils, and mast cells, and the expression levels of thymic stromal lymphopoietin (TSLP) and periostin were also investigated. Evaluation showed an increase in the number of dermal IL‐31+ cells and IL‐31RA+ cells in PH and PVe. Epidermal expression of IL‐31RA increased in PV, PF, and PVe, but not in PH, compared to healthy individuals. The number of dermal eosinophils and basophils was also increased in PVe and PH. The number of dermal mast cells and expression levels of TSLP and periostin did not change among pemphigus subtypes and healthy controls. Collectively, enhanced IL‐31/IL‐31RA signaling and the increased numbers of dermal eosinophils and basophils may participate in itching in PH. On the other hand, IL‐31/IL‐31RA signaling seemed unable to provoke itching in PVe, a non‐pruritic subtype of pemphigus, although it might contribute to epidermal thickening and dermal fibrosis.

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Dear Editor, Mechanical stimuli can provoke an itch sensation, known as 'mechanical itch' or 'touch-evoked itch'. 1 An increase in sensitivity to touch-evoked itch (STTI) by pinprick stimuli is referred to as punctate hyperknesis. 2,3 Punctate hyperknesis can be found in patients with chronic itch conditions and is as debilitating as the itch itself. Its pathogenesis is reported to involve IL-4/13 and IL-31 signalling. 2,4 Prurigo nodularis (PN), a neuroimmune skin disease with multiple pruritic nodules, features chronic itch. 5 However, it is unclear whether PN patients show punctate hyperknesis. Therefore, we examined STTI in patients with PN and investigated the dermal expression of IL-4, IL-13 and IL-31 through immunohistochemical analysis in this cross-sectional pilot study. We enrolled 11 Japanese patients with PN (eight males and three females; age, 12-81 years old; three patients had atopic dermatitis [AD]) and nine healthy individuals without AD (eight males and one female; age, 18-43 years old). STTI was assessed as the mean value of itch intensity resulting from stimulation with preoptimized von Frey filaments (1.0, 1.4 and 2.0 g; Danmic Global, USA), rated on a numerical rating scale (NRS) from zero (no itch) to 10 (the worst imaginable itch). 2,6 STTI was probed on the slope (not the center) of the nodules located on the extremities (five patients) or on the trunk (six patients), and

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