A surprising case of Mycobacterium avium complex skin infection in an immunocompetent patient

An acute inflammatory nodule of unknown etiology can pose a formidable diagnostic challenge. Here, we highlight the importance of including Mycobacterium avium intracellulare complex (MAC) and other atypical mycobacterial infections in the differential diagnosis of a cutaneous nodule in an immunocompetent individual. We also explore the implications of eczema in the development of a mycobacterial infectious process. We report a case of MAC skin infection in an immunocompetent individual. The patient is a 49-year-old male with a history of dyshidrotic eczema presenting with a fluctuant, non-draining nodule on his right forearm for 2 to 3 weeks, identified by tissue DNA probe to be a cutaneous MAC infection without systemic complications, as serologies and chest X-ray were unremarkable. MAC should be included in the broader differential diagnosis of deep fungal vs atypical mycobacterial skin infections. Nucleic acid-based assays are an important tool in making a definitive diagnosis, allowing for utilization of appropriate therapy for the specific etiologic pathogen. Given the patient's preceding diagnosis of eczema, it is possible that the compromised skin barrier and dampened cytotoxic Th1 activity predisposed the patient to this infection, typically appreciated in the immunosuppressed, warranting further investigation into the relative risk for atypical mycobacterial infections in the setting of eczema.