Nivolumab-induced localized genital bullous pemphigoid in a 60-year-old male

A 60-year-old man with metastatic renal cell carcinoma presented with a 6-month history of a pruritic, exquisitely painful genital eruption appearing 3 months after initiation of nivolumab. Examination demonstrated a poorly defined, lichenified scrotal plaque studded with erosions, yellow crust, and tense vesicles. There was no other lesion on the body or mucosae. Histopathology revealed a subepidermal blister with a mixed lymphocytic, neutrophilic, and eosinophilic infiltrate. Direct immunofluorescence of perilesional skin demonstrated subclinical blister and linear/fibrillary patchy IgG and IgA along the dermoepidermal junction. Bullous pemphigoid (BP) serologies revealed normal IgG BP230 antibodies and minimally elevated IgG BP180 antibodies. Indirect immunofluorescence revealed positive IgG at the basement membrane ("epidermal pattern") in human split skin and monkey esophagus substrates; no IgA antibodies were detected. The patient was diagnosed with nivolumab-induced localized genital BP (LGBP). BP is a reported adverse effect of immune checkpoint inhibitors including nivolumab; however, cases are typically generalized. LGBP is a rare BP variant typically presenting in children and females; there are few reports of LGBP in adult males. We report a novel case of nivolumab-induced LGBP with unique histopathologic and clinical challenges. LGBP should be considered in patients on immune checkpoint inhibitor therapy with bullous genital eruptions.