A soft tissue lesion caused by Mycobacterium malmoense.

We report a rare case of a soft tissue infection caused by Mycobacterium malmoense in an 88-year-old woman, a former farmer. The patient presented with a non-healing lesion on her right forearm, which had been increasing in size over 2 months. Ultrasound and magnetic resonance imaging (MRI) showed subcutaneous nodular lesions, and the patient was referred to the multidisciplinary soft tissue tumour meeting at our institution. A biopsy was performed, and the histopathological examination revealed granulomatous inflammation with abundant Ziehl-Neelsen-positive microorganisms, indicative of a mycobacterial infection. A polymerase chain reaction (PCR) assay identified Mycobacterium malmoense as the infective agent. Combined antibiotic treatment resulted in a significant clinical improvement. This case raises awareness about this uncommon pathogen, particularly causing soft tissue infections. The report also highlights the features on imaging, its treatment, and the appropriate utilisation of technology to reach a correct diagnosis.