Complete Resolution of Mycobacterium marinum Infection with Clarithromycin and Ethambutol: A Case Report and a Review of the Literature.

A 70-year-old, immunocompetent male presented with mildly painful and pruritic erythematous patches and vesicles on the right dorsal aspect of the distal middle finger present for four weeks. Other skin lesions or systemic symptoms were notably absent. The patient failed to respond to valacyclovir, topical triamcinolone acetonide ointment, trimethoprim-sulfamethoxazole, and cephalexin for presumptive diagnoses of recurrent herpetic whitlow, dyshidrotic eczema, and blistering distal dactylitis, respectively. Furthermore, biopsy findings were inconsistent with eczema, psoriasis, or viral or fungal infection as potential etiologies. Mycobacterium marinum infection was then considered due to the patient's observation that the lesion appeared three weeks after purchasing a home fish tank. Mycobacterium marinum, referred to as "fish tank granuloma" as a result of its typical association with aquarium exposure, is usually diagnosed clinically and treated empirically due to the organism's slow-growing nature. In light of the infection's low prevalence, large studies regarding treatment options are limited. Our patient's lesion resolved within two weeks of treatment with clarithromycin (500mg twice a day) and ethambutol (15mg/kg once a day), which was then continued for two more months. Prior to this treatment, the patient's lesion had cleared completely with minocycline; we attribute recurrence to not continuing therapy past lesion resolution.