Cutaneous MAC infection in an immunocompetent patient: a case report confirmed by mNGS

Cutaneous infections caused by non-tuberculous mycobacteria (NTM) are rare. Atypical clinical manifestations and the need for precise microbiological identification often result in misdiagnosis and underdiagnosis.

A 65-year-old immunocompetent female initially presented with papular urticaria. Her symptoms improved transiently after anti-inflammatory treatment, but the lesions rapidly progressed to generalized erythematous nodules and ulcers accompanied by fever and lymphadenopathy. Routine microbiological culture and histopathological examination yielded negative results, while metagenomic next-generation sequencing (mNGS) identified Mycobacterium avium complex (MAC) as the causative pathogen.Triple antimicrobial therapy (clarithromycin, doxycycline, and levofloxacin) a favorable clinical response. This case indicates that cutaneous non-tuberculous mycobacterial (NTM) infection has atypical clinical manifestations and is frequently misdiagnosed as common cutaneous eruptions. mNGS can serve as a key diagnostic tool for suspected cutaneous NTM infection, effectively reducing misdiagnosis and missed diagnosis and providing a reliable basis for clinical diagnosis and treatment.

Cutaneous MAC infection, though rare, may occur in immunocompetent individuals. Clinicians should suspect NTM infection in treatment-refractory skin lesions. mNGS is valuable for etiological diagnosis when conventional tests are negative.