Mycobacterium marinum infection successfully treated with oral administration of minocycline and thermotherapy.

Abstract

We report a case of a woman presenting with an erythematous finger nodule, with a history of exposure to tropical fish. The erythematous nodules subsequently spread proximally from the finger. Initial treatment with oral amoxicillin-clavulanate was unsuccessful, and she developed a drug eruption. Treatment with oral minocycline and thermotherapy was initiated, as we suspected infection with Mycobacterium marinum (M. marinum) from her history and clinical features. A culture from a skin biopsy from the finger grew M. marinum, confirming the diagnosis. There is no established treatment regimen for skin infections caused by M. marinum. In this case, it took time for cultures to confirm the diagnosis of non-tuberculous mycobacterial infection. While it would be ideal to await culture results, we felt it was better for the patient to initiate treatment, and in M. marinum infections, minocycline is considered particularly effective. However, it was envisaged that this would result in a prolonged treatment course, leading to potential resistance. Thermotherapy was added in an attempt to shorten the treatment period. This regime was successful, and the patient has remained free of recurrence since. The early initiation of treatment for cutaneous non-tuberculous mycobacterial infection requires aggressive suspicion. Also, testing, including adequate sampling and culturing, is essential for an accurate diagnosis. Slow-growing mycobacteria may take several months to be definitively diagnosed, as they grow only under certain conditions. Therefore, thorough clinical history-taking and information sharing with the microbiology team are essential. Our case illustrates this, and we believe this has important educational value.