Background Acantholysis has been described in biopsies of pityriasis rubra pilaris (PRP), but this has not been emphasized in the dermatology literature. It is helpful for dermatologists to associate acantholysis with PRP in the correct clinical setting. Objective This study aims to further elucidate the clinical context and associated histologic features of acantholysis in PRP. Methods Eight cases of PRP with acantholysis, 16 other cases of PRP, 26 cases of psoriasis, and 17 cases of erythroderma of different causes were studied in an academic setting. Results The presence of acantholysis initially confounded the diagnosis in two cases of PRP. Acantholysis was focal or extensive and resembled Darier's disease, Hailey-Hailey disease, or pemphigus vulgaris. Acantholysis was seen in biopsies from early, isolated papulosquamous lesions from the trunk as well as from erythroderma. By comparison, 26 cases of psoriasis and 17 cases of erythroderma showed only focal acantholysis in two cases of erythroderma. Conclusions Acantholysis is a histologic feature of PRP and can serve as a histologic clue to the diagnosis of PRP before the onset of erythroderma. Eosinophils and/or a lichenoid infiltrate may also be evident.
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