Mycobacterium abscessus Cutaneous Infection in the Immunosuppressed: A Case Report on an Atypical Pathogen.

Mycobacterium abscessus complex (MAbc) is a rapidly growing nontuberculous mycobacterium that represents an increasingly prevalent cause of skin infections. This report describes an atypical presentation of MAbc to heighten physician awareness of the pathogen. A 69-year-old woman with immunocompromised status presented with a 4-month history of a solitary, nonhealing ulcer on her right lower extremity after an insect bite. After no improvement following oral amoxicillin/clavulanate and topical mupirocin for the initial diagnosis of cellulitis, biopsy and culture of the lesion revealed MAbc. Microscopic examination revealed reactive cutaneous inflammation without evidence of malignancy. Acid-fast bacteria (AFB) stain was negative, and no granulomas were noted histologically. Clarithromycin and doxycycline were initiated while awaiting susceptibility testing results. Final culture showed MAbc sensitive to amikacin, cefoxitin, and clarithromycin. Unfortunately, before antibiotic therapy could be modified, the patient died. The presentation of a solitary lower-extremity ulcer is rare compared with current literature. This case occurred after a suspected insect bite rather than instrumentation. In addition, this case demonstrated negative AFB stain and absence of granulomas on histologic analysis. The patient's death did not allow for evaluation of treatment efficacy. Existing literature characterizing MAbc is sparse. Most cases present as multiple papules, nodules, and abscesses with positive AFB staining and granulomas; it is possible for deviations to exist depending on host immune status. Considering the highly drug-resistant nature of M abscessus, prompt diagnosis and treatment are crucial. For this to occur, clinicians must maintain high clinical suspicion for M abscessus infection in any chronic, nonhealing wound failing to respond to initial treatment.