Track

Case Reports

Abstract

Bullous pemphigoid (BP) is the most common autoimmune blistering disorder in adults, caused by autoantibodies targeting hemidesmosomal skin components. Drug-induced BP is often histologically indistinguishable from idiopathic BP, posing a diagnostic challenge. Pembrolizumab, an anti-PD 1 monoclonal antibody used for advanced malignancies, can trigger cutaneous immune-related adverse effects, including BP.

A 66-year-old female with metastatic melanoma on pembrolizumab developed months of pruritic, painful blisters involving the extremities, upper back, genital area, and oral mucosa. Shave biopsies from these lesions showed erosive and ulcerated skin with underlying granulation tissue and rare dermal eosinophils. An acute adverse drug reaction to pembrolizumab was favored, and steroids were initiated. A week later, bullae formed. Punch biopsies revealed subepidermal bullae with a few eosinophils intermixed with neutrophils. Direct immunofluorescence showed strong linear IgG and C3 at the dermal-epidermal junction, supporting a diagnosis of pembrolizumab-induced BP. The low eosinophil count was likely secondary to prior steroid therapy. In addition to the rash, she reported pain with ambulation, limited range of motion, reduced oral intake, and weight loss. Relevant history included atopic dermatitis, presumed Behcet’s syndrome, and hypothyroidism. Pembrolizumab was discontinued and prednisone given during hospitalization resulted in mild improvement of the rash. Outpatient therapy with dupilumab, dapsone, and doxycycline led to symptomatic improvement. This case highlights diagnostic challenges of autoimmune blistering diseases and underscores the importance of correlating clinical findings with a detailed medication history and timeline.