Rare skin manifestation of Mycobacterium marinum, lesion on shoulder: a case report

Abstract

Mycobacterium marinum causes sporadic skin infection. It mostly appears on extremities with erythematous or bluish papule or nodule at the inoculation site, usually after skin abrasions are exposed to contaminated water or fish. A 43-year-old male patient with no prior medical history noticed the appearance of red lesions on the back of his left shoulder 2 years earlier. Various physicians visited the patient and misdiagnosed as contact dermatitis. Physical examination revealed polycyclic livid plaques with irregular hyperkeratosis on the back of his left shoulder. Eventually it was reported he carried a fishing net on his shoulder near the time lesions appeared. So, with suspicion of Mycobacterium marinum, skin biopsies were performed and histopathology showed epidermis with acanthosis and parakeratosis. The dermis showed severe infiltration of neutrophils and lymphoplasma cells with the presence of few giant cells and poorly defined granulomas indicating acute or chronic necrotizing granulomas. Within three weeks of starting treatment with oral clarithromycin, rifampin and co-trimoxazole, signs of improvement began. The manifestation of this disease and its site of involvement in this patient was very rare among previous case reports, so it was considered necessary to be reported.