Atypical Mycobacterium fortuitum Ulcer in an Immunosuppressed Patient With Lupus: A Case Report.

A 65-year-old woman with systemic lupus erythematosus (SLE) on methotrexate and prednisone presented to the dermatology clinic with a chronic, painful ulcer on the right lower leg. The initial differential diagnosis included pyoderma gangrenosum and vasculitis. However, biopsy and wound cultures ultimately revealed Mycobacterium fortuitum. The patient was treated successfully with moxifloxacin and trimethoprim-sulfamethoxazole for four months, resulting in complete ulcer resolution. This case highlights the importance of considering atypical mycobacterial infection in chronic non-healing ulcers, particularly in immunosuppressed patients, and demonstrates the need for early tissue cultures to guide appropriate antimicrobial therapy.