Mycobacterium marinum Granuloma in a Fisherman

While fishing in the Chesapeake Bay, an 81-year-old man slipped and fell into the water. Afterward, he noticed a superficial abrasion over his right knee. During the next 10 days, red bumps, pustules, and slight tenderness developed. He was treated empirically with mupirocin oint- ment, amoxicillin/clavulanate and subsequently with cephalexin. However, new papular lesions continued to develop adjacent to the area of involvement, which showed no signs of healing. Eight weeks after the injury, the patient presented with a 3 × 4-cm patch of densely packed 0.5- to 1.5-mm papules with background erythema (Figure 1). A wedge incisional biopsy was performed. One-half of the specimen was sent for histopathological examination, including periodic acid-Schiff and acid-fast bacillus (AFB) stains. Results showed necrotizing granulomatous inflammation of the superficial and deep dermis with associated ulceration and AFB within the granulomatous inflammation, consistent with Mycobacterium marinum granuloma (Figure 2). The other half of the specimen was sent for bacterial, fungal, and atypical mycobacteria cultures; however, these were not completed because of a processing error in the laboratory. Treatment with minocycline (100 mg PO bid for 6 weeks) led to complete resolution without any recurrence 6 months later.