Successful Nemolizumab Treatment of Refractory Acquired Reactive Perforating Collagenosis in a Diabetic Patient.

Acquired reactive perforating collagenosis (ARPC) is a rare dermatosis associated with diabetes mellitus, characterized by transepidermal elimination of collagen and intense pruritus. We report the case of a 77-year-old Japanese woman with poorly controlled diabetes who developed multiple pruritic, keratotic nodules on her chest, back, and limbs. Histopathological examination revealed full-thickness epidermal defects with prominent transepidermal elimination of thickened collagen fibers, along with dense lymphocytic and neutrophilic infiltrates in the dermis, findings consistent with ARPC. Despite improved glycemic control, her skin lesions and pruritus persisted. Treatment with subcutaneous nemolizumab (60 mg every four weeks), an anti-IL-31 receptor A monoclonal antibody, resulted in complete resolution of pruritus and marked flattening of the skin lesions within two months. This case highlights the potential role of IL-31-targeted therapy in managing refractory ARPC. The clinical improvement observed with nemolizumab suggests it may be a promising therapeutic option in selected cases; however, further studies are warranted to confirm its efficacy.