Pembrolizumab-associated exacerbation of lichen planopilaris in a patient with metastatic melanoma

Introduction: Immune checkpoint inhibitors (ICIs) can trigger cutaneous immune-related adverse events (irAEs), including rare follicular eruptions such as lichen planopilaris (LPP). Case Report: We report a 75-year-old woman with stable, biopsy-proven LPP who developed disease reactivation after ten cycles of pembrolizumab for stage IIC melanoma. Management & Outcome: Despite ongoing treatment with hydroxychloroquine and topical clobetasol, disease activity progressed. Oral doxycycline was added. After ten months of adjunctive therapy and completion of pembrolizumab, the disease stabilized, though areas of scarring alopecia persisted. The patient remains under multidisciplinary follow-up. Discussion: LPP is an underrecognized follicular irAE. The timing, clinical course, and histopathologic findings suggest pembrolizumab-induced exacerbation. Causality was assessed using the Naranjo Algorithm, with a score of 6, indicating a probable adverse drug reaction. This case reinforces the importance of early recognition and tailored dermatologic care in patients receiving ICI therapy.