Isolated subcutaneous nontuberculous mycobacterial infection: a rare case initially mischaracterized as a soft tissue malignancy.

The occurrence of nontuberculous mycobacterial (NTM) infection is rare, and the involvement of the musculoskeletal system is even less common. However, the incidence of soft tissue and skin NTM infection is increasing, particularly in patients who undergo injections and minor surgical procedures. Given the non-specific clinical manifestations of NTM infection, the lack of knowledge among physicians regarding this rare infection could lead to inaccurate and delayed diagnosis. Herein, we present a case of an isolated subcutaneous NTM infection caused by Mycobacterium abscessus in the upper back of an immunocompetent 68-year-old woman. The clinical presentation, magnetic resonance imaging findings (including diffusion-weighted imaging), and pathologic findings of subcutaneous NTM infection are described and compared with those of tuberculosis and tumor presentations to provide a more accurate clinical picture for a differential diagnosis.