Genetically Confirmed Localized Perianal Hailey-Hailey Disease Successfully Treated With Topical Difamilast: A Case Report.

Hailey-Hailey disease, also known as familial benign chronic pemphigus, is a rare autosomal dominant acantholytic dermatosis caused by abnormalities in ATP2C1. The disease typically affects intertriginous areas such as the axillae and groin, whereas localized involvement limited to the perianal region is exceptionally rare. We report the case of a 48-year-old woman who presented with pruritus and pain in the perianal region for one year. The lesion had been refractory to topical corticosteroid therapy. Physical examination revealed a brownish, thickened plaque with erosion and maceration around the anus. Histopathological examination demonstrated suprabasal clefting and acantholysis, creating a dilapidated brick wall appearance. Direct immunofluorescence staining was negative. Genetic analysis identified a donor splice-site mutation in ATP2C1 (c.899+1G>T), confirming the diagnosis of Hailey-Hailey disease. Treatment with topical difamilast, a phosphodiesterase-4 inhibitor, led to improvement of pruritus and gradual epithelialization of the erosion over two months, with no recurrence during seven months of follow-up. Localized perianal Hailey-Hailey disease is an important diagnostic consideration in chronic treatment-resistant perianal erosions. This case highlights the value of careful clinicopathological evaluation and genetic testing in atypical presentations and suggests that topical difamilast may be a useful therapeutic option for localized disease.