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Case Reports

Abstract

An 80-year-old man with chronic lymphocytic leukemia (CLL) and atrial fibrillation on apixaban presented with a nine-month history of asymptomatic ecchymotic plaques, which started on the dorsal forearms. Three weeks prior to onset, he began acalabrutinib, a second-generation Bruton tyrosine kinase (BTK) inhibitor, for CLL. He was initially diagnosed with solar purpura. However, the eruption progressed over several months, involving the upper arms and, to a lesser extent, the lower back and abdomen. Examination revealed well-demarcated red-brown plaques with ecchymoses and petechiae. The eruption strikingly spared the watch line, antecubital fossae, and t-shirt lines. Two punch biopsies were performed on the bilateral upper arms and showed mild superficial perivascular lymphohistiocytic inflammation with rare eosinophils and numerous extravasated erythrocytes. A diagnosis of BTK inhibitor–induced eruption, compounded by factor Xa inhibitor use, was made.

BTK inhibitors are commonly used in the treatment of advanced CLL and work through inhibition of B-cell receptor signaling and tumor microenvironment interaction. Cutaneous adverse events, more common with first-generation agents, range from isolated petechiae and purpura to severe dermatoses including blistering and vasculitis eruptions. Photo-distributed purpuric eruptions have been infrequently described, typically arising 3–4 weeks after therapy initiation due to drug-induced platelet dysfunction. Histopathology is nonspecific, often showing erythrocyte extravasation and mild superficial perivascular inflammation. Lesions typically resolve within months after discontinuation. Management focuses on emollients and photoprotection. This case underscores the importance for clinicians and dermatopathologists to understand the spectrum of BTK inhibitor–associated cutaneous reactions to prevent misdiagnosis and unnecessary cessation of therapy.