Abstract: A 48-year-old female presented with nodules on the left knee for 16 months. The patient had been treated with itraconazole and dapsone in another hospital for 9 months, with ineffective. The patient was diagnosed with Mycobacterium marine infection by mycobacterium culture and quantitative polymerase chain reaction (qPCR) technique of skin tissue in our hospital. After 4 months of oral rifampicin and clarithromycin, the skin lesions were significantly improved. The time from the onset of skin symptoms to the diagnosis of mycobacterium marine infection was 16 months, which reminds dermatologists should be aware of the atypical clinical manifestations of Mycobacterium marinum infection.

Key words: Mycobacterium marinum infection, erythema elevatum diutinum, misdiagnose