Tenosynovitis caused by Mycobacterium malmoense

Mycobacterium malmoense is a slow-growing nontuberculous mycobacterium (NTM) increasingly recognized as a cause of extrapulmonary infections. Tenosynovitis due to M. malmoense is rare and diagnostically challenging because of its indolent course and nonspecific clinical presentation.

We report a 65-year-old immunocompetent woman presenting with progressive wrist pain, swelling, and impaired hand function without prior trauma. Symptoms developed after exposure to fresh fish and shellfish. Surgical exploration revealed extensive tenosynovitis with median nerve compression. Histopathology showed granulomatous synovitis suggestive of mycobacterial infection. Molecular testing detected Mycobacterium genus DNA, while PCR for the Mycobacterium tuberculosis complex was negative. After prolonged incubation, culture identified M. malmoense. Drug susceptibility testing demonstrated susceptibility to standard antimycobacterial agents except doxycycline. Initial empiric therapy targeting M. marinum was adapted following species identification. After 8 months of treatment, significant clinical and radiological improvement was observed, with no evidence of relapse at 6-month follow-up.

M. malmoense tenosynovitis is extremely rare, with only few cases reported. Diagnosis is frequently delayed due to low sensitivity of microscopy, slow growth in culture, and nonspecific findings. Molecular diagnostics and prolonged incubation are essential. Management requires a combination of surgery and prolonged antimycobacterial therapy.

NTM infections, including M. malmoense, should be considered in chronic tenosynovitis unresponsive to standard treatment. Early diagnostic suspicion and interdisciplinary management are crucial for favorable outcomes.