Abstract
Pembrolizumab is an immune checkpoint inhibitor that has been associated with numerous immune-mediated adverse effects. Several of these cutaneous side effects may include bullous pemphigoid, Stevens-Johnson syndrome, and drug reaction with eosinophilia and systemic symptoms (DRESS). Other case reports have reported DRESS as a rare side effect of immune checkpoint inhibitors but due to its variable presentation and similarities with other cutaneous diseases, it has proven to be a diagnostic challenge. In addition, no effective methods have been developed to monitor for such adverse skin reactions in patients on immunotherapy. Here, we report a diagnostic challenging case of pembrolizumab-induced blistering lesions that were initially treated as suspected Herpes zoster and/or bullous pemphigoid but further pathology was consistent with DRESS.