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Abstract

Lichen planus pemphigoides (LPP) is a rare immune-mediated dermatosis with features of both lichen planus (LP) and bullous pemphigoid (BP) that often occurs with medication exposure. It is considered a distinct clinical entity secondary to autoantibodies primarily targeted against BP180 and BP230.

We report a 63-year-old female with metastatic endometrial cancer on pembrolizumab maintenance therapy who presented with a six-week history of erythematous, blistering, and erosive lesions beginning on the feet and spreading to the lower legs and forearms. She had been treated with oral methylprednisolone, debridement, ciprofloxacin, and amoxicillin-clavulanate for presumed cellulitis without improvement.  Dermatologic evaluation revealed violaceous papules and plaques with vesiculation and scaling. Two calf biopsies showed lichenoid dermatitis, and direct immunofluorescence (DIF) demonstrated weak linear IgG and moderate C3 deposition at the basement membrane zone. In the clinical context, these findings supported a diagnosis of lichen planus pemphigoides. The patient received an oral steroid taper, calcium and vitamin D supplementation, and topical clobetasol, with good response on follow-up.

LPP has been reported as an adverse effect of pembrolizumab, most often in other malignancy types. This case highlights the importance of considering an immunobullous process in patients who present with eruptions during immune checkpoint inhibitor therapy, even when morphology is not characteristic. Inclusion of both H&E and DIF evaluation is important to avoid misdiagnosis and ensure prompt treatment. Further studies are needed to clarify risk factors, pathogenesis, and optimal management of immunotherapy-associated LPP, and clinicians should maintain a low threshold for DIF in suspected immunotherapy-related cutaneous events.