A case of bullous pemphigoid following administration of anti‐IL‐31 receptor A antibody

Abstract Bullous pemphigoid (BP), an autoimmune bullous dermatosis, occurs predominantly in older individuals. Nemolizumab, a humanized monoclonal antibody against the interleukin (IL)‐31 receptor A, is used to treat severe atopic dermatitis (AD) in Japan. However, it can cause several adverse events, such as exacerbation of AD, erythema, and eosinophilia. Herein, we describe a case of prurigo‐type AD developing BP after nemolizumab administration. A 62‐year‐old man with prurigo‐type AD and asthma presented with serious, refractory itching. After nemolizumab injection, his pruritus was relieved for 2 days. However, on day 3, erythema with blisters and erosions suddenly appeared throughout his body. Pathological examination showed typical BP and the patient's serum anti‐BP180‐NC16a antibody level was 882.5 U/mL. Oral prednisolone (PSL) was initiated and nemolizumab was never used again. Despite high‐dose PSL, new blisters continued to develop, with a rapid elevation of anti‐BP180‐NC16a antibodies to 6930 U/mL. Adding high‐dose cyclosporine and intravenous gamma globulin reduced new blister formation after 9 weeks, and PSL and cyclosporine were gradually tapered. Dupilumab, an anti‐IL‐4 receptor antibody, was initiated after 16 weeks, resulting in continued remission without PSL and cyclosporine. The sudden occurrence of BP in this case suggested that the patient had occult BP before the nemolizumab initiation and that nemolizumab exacerbated BP and made it overt. Blocking the IL‐31 pathway may exacerbate inflammation in AD or BP, resulting in the acceleration of blister formation. This may be countered by blocking the IL‐4/13 pathway with dupilumab. To our knowledge, this is the first case of nemolizumab‐exacerbated BP.