Diagnostic Challenges of Multiple Sporotrichoid Skin Lesions Caused by Mycobacterium marinum

BACKGROUND Mycobacterium marinum is a slow-growing non-tuberculous mycobacterium that is known to cause skin and soft tissue infections, even in healthy patients, and is commonly associated with fish and aquatic environments. CASE REPORT A 23-year-old man working in aquarium management presented with a chronic progression of multiple skin nodules on his right forearm and thumb. The patient was referred from the Dermatology Department to the Outpatient Clinic due to suspected skin tuberculosis, as indicated by a positive T-SPOT.TB test. A second excisional biopsy tested positive for M. marinum via PCR sequencing by the National Institute of Infectious Diseases, confirming the diagnosis. The initial treatment consisted of rifabutin at 300 mg/day and clarithromycin at 800 mg/day. However, due to liver dysfunction, the regimen was changed to moxifloxacin at 400 mg/day and rifabutin. Moxifloxacin was discontinued due to nausea. Finally, the treatment was adjusted to linezolid at 1200 mg/day and clarithromycin. The patient's skin condition improved, with the nodular lesions showing a trend toward resolution. Culturing is time-consuming, and the sensitivity can be reduced when using N-acetyl-l-cysteine-sodium hydroxide in the pre-treatment process; therefore, caution with its use is necessary. Pathological examination can initially show inflammatory changes, and granulomatous lesions with caseous necrosis are not always present. Antibiotics such as rifampicin, rifabutin, moxifloxacin, and clarithromycin are used, but there is scant evidence for treatment regimens, often resulting in prolonged monotherapy or combination therapy. CONCLUSIONS In cases presenting chronic lesions resembling multiple sporotrichoid forms, repeated biopsies are crucial due to the challenges associated with culturing.