Disseminated Cutaneous Infection with Mycobacterium chelonae in a Renal Transplant Recipient
Mycobacterium chelonae belongs to a rapidly growing group of nontuberculous mycobacteria (NTM). These organisms are environmental saprophytes that can cause infection in humans. Nontuberculous mycobacteria infections have been described in immunosuppressed patients (eg, in the setting of AIDS or immunotherapy following solid organ transplantation) as well as in immunocompetent patients with certain predisposing factors (eg, recent history of a traumatic wound, recent drug injections, impaired cell-mediated immunity). Due to the increasing prevalence of immune deficiency disorders as well as the rising number of cosmetic procedures performed on healthy individuals, NTM may become a frequent cause of serious morbidity, causing chronic infections of the skin, soft tissue, and lungs. We report a case of M chelonae infection in a 61-year-old woman who was receiving immunosuppressive therapy following renal transplantation 6 years prior to presentation. It is important for clinicians to consider NTM in the differential diagnosis for patients who present with chronic skin or soft tissue infections.
Practice Points
- Nontuberculous mycobacteria (NTM) are environmental saprophytes that can cause infection in immunosuppressed individuals as well as immunocompetent individuals with certain predisposing factors.
- It is important for clinicians to consider NTM in the differential diagnosis for patients who present with chronic skin or soft tissue infections.
- Histologic examination and culture of a biopsy specimen followed by polymerase chain reaction assay for genotyping of the specimen are recommended to determine the responsible Mycobacterium species.
- New molecular genetic strip tests can differentiate NTM species more quickly.
Immunosuppression associated with treatment following renal transplantation was the primary cause of M chelonae infection in our patient, as has previously been reported in the literature.3-4 This was further supported by the lack of prior trauma or invasive procedure (eg, mesotherapy) in the affected areas. Specifically, our patient had more than 5 lesions on the lower legs; in accordance with a previous comprehensive study,1 the presence of more than 5 lesions indicates a disseminated cutaneous infection, which usually is correlated with immunosuppression (such as in our patient). Localized infections generally are observed in immunocompetent hosts.1
The exact pathogenetic mechanism of M chelonae infection in our patient is not clear. In patients with suppressed immunity, the variable clinical presentation of infection with NTM often impedes diagnosis. Cutaneous M chelonae lesions may be mistakenly diagnosed as Kaposi sarcoma or rarely as pyoderma gangrenosum. The differential diagnosis of subcutaneous nodules includes histoplasmosis, cryptococcosis, blastomycosis, coccidioidomycosis, nocardiosis, mycetoma, sporotrichosis, actinomycosis, and tuberculosis. In our patient, approximately 2 months elapsed between presentation of symptoms and definitive diagnosis, which was less than that reported in previously published cases.2,7-9
Histology and tissue culture followed by proper genetic analysis remains the gold standard for diagnosing NTM infection.10,11 In the interest of patients, time-consuming biochemical analyses should be replaced by molecular genetic diagnostic strip tests, which are fast, exact, and available in commercial kits for both common mycobacteria and additional species.12
Once the diagnosis of NTM infection has been established, sensitivity testing is mandatory to guide targeted therapy; however, clinicians should bear in mind that susceptibility testing does not guarantee clinical success, as correlations of susceptibility testing and clinical response have not been assessed.8 Standard antituberculous drugs (eg, isoniazid, rifampin, pyrazinamide) have no role in the treatment of M chelonae infection. The first-line antibiotics are clarithromycin, tobramycin, and linezolid, followed by imipenem, amikacin, clofazimine, doxycycline, and ciprofloxacin.10 Optimal outcomes have been reported in patients treated both with antibiotics and with surgical debridement. Although monotherapy with quinolones is not recommended for treatment of infection with NTM due to the high risk of mutational resistance, our patient received long-term antibiotic treatment with ciprofloxacin over a 6-month period and showed no recurrence at 24-month follow-up.
Conclusion
Clinicians who treat patients with chronic skin or soft tissue infections should consider infection with NTM in the differential diagnosis, particularly in patients with suppressed immunity, but also in immunocompetent patients following any invasive procedure. Detailed medical history and skin biopsy followed by histology and culture are recommended for the diagnosis. Infection with NTM requires rapid action. Sensitivity testing is necessary in choosing an effective treatment. New molecular genetic diagnostic strip tests can differentiate species of NTM sooner than biochemical analyses, thereby helping clinicians initiate appropriate antimicrobial treatment in a timely fashion.
