Multifocal cutaneous Mycobacterium chelonae infection in a patient with lung cancer and skin lesions mimicking metastasis: a diagnostic and therapeutic challenge and case report

Mycobacterium chelonae is a rapidly growing nontuberculous mycobacterium that can cause severe infection in immunocompromised hosts. Cutaneous involvement may closely resemble metastatic disease, creating substantial diagnostic uncertainty, particularly in patients with advanced malignancy. A 68-year-old Asian man with stage IVB epidermal growth factor receptor-mutated lung adenocarcinoma, who was receiving systemic anticancer therapy and long-term dexamethasone, developed multiple progressive, painless subcutaneous nodules. Positron emission tomography–computed tomography demonstrated intense fluorodeoxyglucose uptake (maximum standardised uptake value 12.02), strongly suggesting cutaneous metastases. Initial skin biopsies were nondiagnostic. Approximately 4 months later, performance status (PS) worsened from 2 to 3; a repeat biopsy revealed tissue resembling pyogenic granuloma inflammation, and culture of purulent material from an open lesion grew M. chelonae , establishing a diagnosis of multifocal cutaneous nontuberculous mycobacterial infection. Targeted antimicrobial therapy with amikacin, azithromycin, and sitafloxacin resulted in marked improvement in the cutaneous lesions and PS from 3 to 2. Although further disease-directed treatment was limited, this improvement allowed the patient to resume S-1 chemotherapy in accordance with his treatment goals. Chemotherapy was continued briefly before disease progression required transition to best supportive care. Multifocal cutaneous M. chelonae infection should be considered in immunosuppressed patients with cancer presenting with new or progressive skin lesions, even when imaging findings strongly suggest metastatic disease. Early biopsy with mycobacterial culture and individualised treatment planning are essential for maintaining patient-centred care and quality of life.