Elusive Diagnosis of Recurrent Subcutaneous Emphysema: Nocardia farcinica Infection in an Immunocompetent Female Patient.

This case report describes an immunocompetent female with recurrent subcutaneous emphysema and refractory soft tissue infections involving multiple non-contiguous sites-bilateral breasts, chest wall, and upper limb-over seven years, consistent with disseminated nocardiosis. Initial presentations mimicked bacterial mastitis, with localized swelling, erythema, crepitus, and elevated inflammatory markers. Despite repeated incision and drainage procedures, antibiotic therapies, and bilateral mastectomies, symptoms recurred persistently. Conventional microbial cultures repeatedly failed to identify a pathogen, while metagenomic next-generation sequencing (mNGS) of a late-stage chest wall lesion ultimately revealed Nocardia farcinica, an opportunistic actinomycete with a known propensity for systemic dissemination even in immunocompetent hosts. The patient's atypical clinical course-marked by multifocal gas-forming soft tissue necrosis, chronic recurrence, and resistance to empiric treatments-underscores the diagnostic challenges posed by fastidious pathogens like Nocardia. Key lessons include the utility of mNGS in identifying culture-elusive organisms, the importance of considering nocardiosis in refractory subcutaneous infections regardless of immune status, and the necessity of prolonged, targeted antimicrobial regimens (eg, sulfonamides) combined with surgical intervention. This case highlights evolving paradigms in managing complex disseminated infections through advanced genomic diagnostics and multidisciplinary approaches.