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| Fig. 30.6 Swimming pool granuloma caused by M. marinum. A, Erythematous nodule on middle finger with sporotrichoid spread along the afferent lymphatics. B, Close-up of finger nodule. C, Ziehl-Neelsen staining demonstrating numerous acid-fast mycobacteria in a patient with swimming pool granuloma. (Courtesy of James E. Fitzpatrick, MD.) |
It is an inoculation caused by
Mycobacterium marinum, although, very rarely, it can be caused by
Mycobacterium gordonae. M. marinum is ubiquitous in aquatic environments, including both fresh and salt water. The organism is inoculated into the skin through small cuts or abrasions while swimming or cleaning aquariums. Following an incubation period of 2 to 3 weeks (1 week to 2 months in some instances), a small violaceous papule develops at the site of inoculation. The lesion gradually enlarges into a dark red to violaceous plaque. A sporotrichoid pattern may be seen with violaceous nodules along the afferent lymphatics (Fig. 30-6A,B). The most common sites include hands, feet, elbows, and knees (sites prone to trauma). The diagnosis of cutaneous
M. marinum infection is mainly clinical, with supporting evidence from histologic features and the response to therapy (Fig. 30-6C). The lesions typically heal spontaneously but may disseminate. This infection may respond to multiple single and combination antibiotic regimens.
