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Mycobacterium marinum is an environmental, nontuberculous mycobacteria that causes disease in fresh and salt water fish and rarely in humans. It is pathogenic through traumatized skin, and infection typically results in a single bluish-red inflammatory nodule, which forms a crust or small verrucous plaque.1 Usually, the upper extremities are affected,2 and the infection may be self-limited, resolving in months to years.1 We report an atypical case of M. marinum infection in a South Pacific Islander with chronic, progressive large verrucous plaques on the lower extremity.
An otherwise healthy 29-year-old male taro farmer from the Federated States of Micronesia presented to our clinic with an 18-year history of several large, asymptomatic, progressively enlarging lesions on the left foot, left knee, and left upper thigh. Before these lesions appeared, he "scraped" his left knee, soon thereafter noting swelling and redness, which progressively increased in size and became more crusted in appearance. Additional areas of involvement arose, slowly progressing to involve his left foot and left upper thigh as well. He denied any significant pain, itching, fever, or chills. These plaques began while he lived in Micronesia, and at the time of his evaluation, he had lived in the United States for 1 year. Of note, he reported that > 50 people on his native island of Satowan had similar appearing lesions and that they refer to this condition as "spam disease."
On examination, he was a healthy-appearing male with a non-tender, large (~25 cm) verrucous plaque involving the left knee circumferentially, in addition to smaller (8–12 cm) plaques on the dorsal foot and left upper thigh (Figure 1
). He did not exhibit lymphadenopathy. Plaques on the proximal thigh had some scattered pustules.
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The patient was treated with twice-daily doxycycline for 3 months and had a dramatic flattening of the verrucous plaques (Figure 2). He was lost to follow-up for 6 months, during which time he stopped therapy. When he returned, there were islands of recurrence within one flattened plaque (Figure 3). Routine bacterial and fungal tissue cultures were negative again, and tissue culture was positive for M. marinum that was sensitive to all the tested antibiotics above. Therapy was re-instituted with doxycycline. A combination of antibiotics was not instituted because of the patients financial ‘ hardship. Unfortunately, the patient was lost to follow-up, and we have been unable to reassess his response to therapy.
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Both clinically and in vitro, M. marinum has been found to be susceptible to the tetracycline class of antibiotics.4 Our patient was started on doxycycline because of his limited financial resources, and he was continued on monotherapy because of shown clinical improvement during treatment. Despite near clinical resolution, his subsequent recurrence off therapy shows a failure with short-term monotherapy. Thus, combination therapy or prolonged monotherapy may be more efficacious treatment options. Unfortunately, we have been unable to assess his response to long-term monotherapy.
The reason for the distinct morphology and disease course in South Pacific Islanders is unclear. It may be caused by a chronic environmental exposure, a particularly virulent strain of M. marinum, co-infection with another organism, or an underlying genetic predisposition that makes the local population more susceptible. This could also merely be the end result of long-standing untreated M. marinum infection, which is something that this medically underserved population is at particular risk. In our case, his infection started after skin trauma and subsequent continuous exposure to water-filled taro farms where he worked for many years. This report highlights the importance of considering chronic M. marinum infection when seeing otherwise healthy patients from the South Pacific with large verrucous plaques on the extremities. Tissue culture is the key to diagnosis, and combination antimicrobial therapy or long-term monotherapy may be more efficacious than short-term monotherapy.
Received February 26, 2008. Accepted for publication April 2, 2008.
Disclosure: The authors have no conflict of interest to disclose.
* Address correspondence to Joseph V. Lillis, Oregon Health Sciences University, Department of Dermatology, 3303 SW Bond Avenue, CH16D, Portland, OR 97239. E-mail: lillisj{at}ohsu.edu 
Authors’ addresses: Joseph V. Lillis, Oregon Health Sciences University, Department of Dermatology, 3303 SW Bond Avenue, CH16D, Portland, OR 97239, Tel: 503-418-3376. Kevin L. Winthrop, Oregon Health and Sciences University, Departments of Infectious Diseases, Ophthalmology and Public Health and Preventive Medicine, 3375 SW Terwilliger Boulevard, Portland, OR 97239, Tel: 503-494-5496. Clifton R. White, Oregon Health Sciences University, Department of Dermatopathology, 3303 SW Bond Avenue, Portland, OR 97239. Eric L. Simpson, Oregon Health Sciences University, Department of Dermatology, 3303 SW Bond Avenue, CH16D, Portland, OR 97239, Tel: 503-494-3968, Fax: 503-494-6968, E-mail: simpsone{at}ohsu.edu.
Reprint requests: Joseph V. Lillis, Oregon Health Sciences University, Department of Dermatology, 3303 SW Bond Avenue, CH16D, Portland, OR 97239, E-mail: lillisj{at}ohsu.edu.
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