Acute promyelocytic leukemia-associated Sweet's syndrome mimicking an axillary abscess: A case report with review of literature.

A subcutaneous painful left axillary nodule was clinically diagnosed as abscess. Fine-needle aspiration biopsy (FNAB) revealed smears full of mature neutrophils. Background was free of fibrinous necrotic material and degenerating and necrotic neutrophils, which is characteristic of abscess. No organisms were detectable on special staining, and culture was sterile. A cytological differential diagnosis of abscess or Sweet's syndrome (SS) was offered, and the latter was confirmed. SS, also known as acute febrile neutrophilic dermatosis, shows diffuse dermal neutrophilic infiltrate without vasculitis on biopsy. Our case is probably the first where SS was diagnosed on FNAB. SS is a differential diagnosis for painful skin nodules. FNAB smears of painful skin nodules that yield abundant neutrophils should be carefully evaluated for necrosis, fibrin and degenerated neutrophils. The absence of these in an appropriate clinical setting points towards a neutrophilic dermatosis like SS.