Clinicopathological Challenge: A Rapidly Progressive Bullous Ulcer in a Patient Receiving Gilteritinib.

Neutrophilic dermatoses are an emerging complication of targeted leukemia therapies and can present diagnostic challenges in immunocompromised patients. We report an 80-year-old woman with therapy-related acute myeloid leukemia who developed a painful violaceous papulonodule on the right shin that rapidly became bullous and ulcerated with intense surrounding hemorrhage 5 months after initiating the FLT3 inhibitor gilteritinib. Histopathology demonstrated a deep neutrophilic infiltrate with negative infectious workup, supporting FLT3 inhibitor-associated bullous pyoderma gangrenosum. The lesion improved following gilteritinib discontinuation and a 12-week corticosteroid taper. This delayed-onset case expands the spectrum of FLT3 inhibitor-associated neutrophilic dermatoses beyond Sweet syndrome.