A 47-year-old woman presents with a lesion that first appeared on her arm two months ago. The lesion has grown increasingly tender and large and has persisted despite a course of antibiotics (cephalexin 500 mg qid for 10 days).

She denies any history of similar problems but does relate a 20-year history of Crohn’s disease. She was recently hospitalized for care of her Crohn’s-related pyoderma gangrenosum, which occured on her legs. Despite all this, the patient otherwise feels well, reporting no fever or malaise.

Examination reveals a woman who looks her stated age, with a 2.5-cm brownish red round plaque located on the dorsal right forearm. Little if any erythema extends beyond the sharply defined border. The surface of the plaque looks slightly blistery, but on palpation the lesion feels solid and not fluid filled. It is moderately tender to touch and much warmer than the surrounding skin. No lymph nodes can be palpated in either epitrochlear or axillary areas, and no similar lesions are seen elsewhere.

ANSWER
The correct answer is Sweet’s syndrome (choice “a”), also known as acute febrile neutrophilic dermatosis. Read on for a discussion of this condition.

Mastocytosis (choice “b”) can present with solitary lesions (“mastocytoma”), but biopsy would have shown a marked increase in mast cells, not the mature polymorphonuclear leukocytes seen in this biopsy. Pyoderma gangrenosum (choice “c”) lesions eventually ulcerate, and biopsy would have revealed a mixed infiltrate instead of the purely neutrophilic one seen. Cellulitis (choice “d”) would have manifested acutely, quickly becoming suppurative, in contrast to the persistence seen with this lesion.

DISCUSSION/TREATMENT
Sweet’s syndrome was first described in 1964 and has since been organized into three basic categories: the classic type, often idiopathic since most cases are of unknown origin; malignancy-associated, typically hematologic (eg, myelogenous leukemia); and drug induced, which was first described in association with sulfa-trimethoprim.

The classic presentation can be triggered by, among other things, upper respiratory infections, pregnancy, and inflammatory bowel disease—as in our patient, whose lesion is quite typical. Arguably the most significant association is with a malignancy, a search for which is undertaken when other possible triggers are absent.

The gold standard for treatment of Sweet’s syndrome is systemic corticosteroids, but other drugs have been used with success, including colchicine and dapsone. This patient is being successfully treated with topical clobetasol cream under occlusion, selected because her disease is very limited. Complete blood count and manual differential diagnosis failed to show any evidence for leukemia.