UPMC Dermatopathology "Case of the Month" Presentations
UPP - Department of Dermatology, Dermatopathology Unit
Case Authors: Robin P. Gehris, MD, Drazen Jukic, MD
NOVEMBER 2003 CASE OF THE MONTH
DISCUSSION & DIAGNOSIS
TISSUE CULTURE:
Gram stain was negative for WBCs
or organisms. Tissue cultures were negative for anaerobic organisms or fungus.
acid fast bacilli.
DNA probes were performed and were negative for Mycobacterium
gordonae and Mycobacterium avium. After 1 month, Mycobacterium marinum was identified.
Sensitivity testing was performed and showed full sensitivity only to Amikacin,
with intermediate sensitivities to Kanamycin, Streptomycin and Minocycline,
and resistance to Doxycycline. Sensitivity testing to Clarithromycin is currently
pending.
Mycobacterium marinum is a member of the nontuberculous family of mycobacteria known as “atypical mycobacteria.” Clinically, lesions should raise one’s clinical suspicion for atypical mycobacteria if they present as indolent ulcers or granulomatous plaques. They occur most often in the setting of immunocompromise; however, they can infect normal hosts if given a portal of entry such as an abrasion, puncture wound or inhalation. The atypical mycobacteria most likely to result in cutaneous infections include M. marinum, M. kansasii, M. ulcerans, M. scrofulaceum, M. avium complex, M. haemophilum, M. fortuitum, M. chelonei and M. abscessus.
The natural hosts for M. marinum are fresh- and salt-water fish. Other vectors include dolphin, shrimp, snails and water fleas. The organism can therefore be found in all types of water, including lakes and swimming pools, aquariums and beaches. Interestingly, it has been found in some cases to be resistant to chlorine. The incubation period ranges from 1 week to 2 months after exposure, with most infections presenting in 2-3 weeks. It classically presents as a “fish tank” or “swimming pool” granuloma, which appears as a solitary blue-red nodule or pustule at the initial site of trauma. It then proceeds to form a crusted ulcer, draining abscess or verrucous nodule. Since the organism grows best at temperatures between 30 and 32 degrees Celsius, it favors acral skin sites. 90% of patients present with involvement of the upper extremity alone. 20-40% of patients present with “sporotrichoid” spread, which is characterized by the appearance of lesions along the draining lymphatics. Additionally, patients with primary hand involvement may present with tenosynovitis of the fingers or hand. Rarely are systemic symptoms or lymphadenopathy found in association with skin infection; the patients are typically well. Of note, however, a PPD may be positive in 50-80% of cases.
The histologic findings in M. marinum infection can be divided into acute and chronic changes. Lesions present for less than 3 months demonstrate epidermal hyperkeratosis, acanthosis and a mixed inflammatory infiltrate composed of neutrophils, lymphocytes and histiocytes. Older lesions may contain tuberculoid granulomas, but caseation necrosis is uncommonly seen. There may be prominent fibrosis and granulation tissue formation. Special stains for acid-fast bacilli include the Ziel-Neelson acid-fast stain or Fite stain, which demonstrate the slender bacilli within histiocytes. In comparison to M. tuberculosis, the bacilli are longer, wider and may show transverse bands. While only 9% of cases in one retrospective review by Edelstein stained positively for the organism, 70-80 % of cases were positive on culture. It is important to notify the laboratory when these organisms are suspected, as they can take several weeks to grow. It is also of value to request sensitivity testing early in the course in order to best direct therapy, as multiple drug resistance patterns may be present. The histologic differential diagnosis of such a granulomatous infiltrate includes foreign body, cutaneous tuberculosis and deep fungal infections.
Current treatment recommendations for skin infections caused by M. marinum consist of some combination of Minocycline, Trimethoprim-sulfamethoxazole, Ethambutol, Rifampin or Clarithromycin. Of the above medications, Clarithromycin is bactericidal as well as safe so is hence recommended as first-line treatment for a total of 12-24 weeks, or at least 4-8 weeks after clinical resolution. For severe or persistent infections, Clarithromycin and Ethambutol may be combined for their synergistic effects, and debridement may be necessary to treat any sinus tract formation, especially if the infection involves the deeper planes of the hand. Excision is not only unnecessary but is relatively contraindicated, as it may precipitate spread of the organism to deeper surrounding tissues. Finally, since the organism grows only at temperatures below 32 degrees Celsius, heating of the extremity with very warm water or a hot lamp may help speed resolution and ultimately shorten the necessary course of antibiotic treatment.
It is most likely that this patient contracted his infection at the site of an inadvertent abrasion or puncture to the left wrist while at the beach; however, other potential sources of the organism are his hermit crab and the wading pool at his daycare. Efforts are presently underway to culture his hermit crab in order to rule out any potential source for reinfection. He is currently being treated with a minimum of 12 weeks of oral Clarithromycin, with the ultimate length of treatment hinging upon rapidity of clinical improvement.
REFERENCES:
Barnhill RL, Busam KJ, Crowson AN, et al. Textbook of Dermatolpathology. 1998.
Bolognia JL, Jorizzo JL, Rapini RP, et al. Dermatology. 2003: 1157-1163.
Browning JC, Miller TD, Metry DW. Index of Suspicion Case 2. Pediatrics in Review. 2003; 24 (11): 387-93.
Edelstein H. Mycobacterium marinum skin infections: Report of 31 cases and review of the literature. Arch Intern Med. 1994; 154: 1359-1364.
Weitzul S, Eichhorn PJ, Pandya AG. Nontuberculous Mycobacterial Infections of the Skin. Dermatologic Clinics. 2000; 18 (2): 359-77. .
