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MYCOBACTERIUM TRIPLEX LUNG DISEASE IN AN IMMUNOCOMPETENT HOST

Saint Louis University School of Medicine, St. Louis, MO

INTRODUCTION: Mycobacterium triplex (M. triplex), a recently described, potentially pathogenic species of mycobacterium, causes disease primarily in immunocompromised patients. A few of cases have been reported in immunocompetent hosts. The clinical importance of M. triplex is often difficult to determine, especially in patients with chronic, pre-existing lung diseases. The diagnosis, treatment regimen and duration of therapy remain undefined. We present a case of pulmonary disease due to this mycobacterium in an immunocompetent patient.

CASE PRESENTATION: An 82-year-old woman was referred to the pulmonary clinic for persistent cough, minimal sputum production, and exertional dyspnea of two years duration. She resided in a suburban area, had a 40-pack-year history of smoking, and quit 10 years ago. There was no history of alcohol abuse or use of any immunosuppressive drugs. She had developed pneumonia twice in the past few years. Physical examination revealed significant kyphoscoliosis and bibasilar crackles. A tuberculin skin test and an HIV test were negative. Computerized tomography (CT) scan of the chest revealed diffuse emphysematous changes, bronchiectasis, and a left lower lobe cavitary lesion. Pulmonary function testing (PFT) showed mild restrictive ventilatory impairment with moderate air-trapping, decreased DLCO, and increased airway resistance. Sputum and bronchoalveolar lavage (BAL) fluid were positive for acid fast bacilli (AFB) using both rhodamine-auramine fluorescent stain and Kinyoun stain, respectively. Mycobacterial culture showed heavy growth of M. triplex. Antimycobacterial therapy with ethambutol, ciprofloxacin, and clarithromycin was started. After an initial 18-month treatment, she experienced improvement of clinical symptoms and tolerated the triple drug regimen. However, there was no significant change in the radiological abnormalities. Two months after stopping the antimycobacterial regimen, the patient started experiencing recurrence of cough and worsening of exertional dyspnea. Sputum cultures were re-sent and the same organism was re-identified. Quadruple antimycobacterial regimen consisting of ethambutol, ciprofloxacin, clarithromycin, and rifampicin was started and resulted in the improvement of the patient’s respiratory symptoms. Fifteen months into the quadruple regimen, sputum AFB smear and mycobacterial culture were negative while the chest CT scan showed no changes in the radiographic abnormalities. PFT showed a 340 ml decrease in FVC, with no significant changes in the FEV1, TLC, and DLCO. The quadruple regimen was eventually discontinued after 21 months, at which time the patient remained symptomatically improved.

DISCUSSIONS: M. triplex, an emerging pathogen which infrequently causes pulmonary disease in immunocompetent patients, appears to be poorly responsive to antimycobacterial chemotherapy. Review of the literature from 1996 to April 2009 yielded 4 reports of pulmonary infections in immunocompetent patients. In these reports, only one patient had pneumonconiosis while the other three had no underlying lung disease when pulmonary infection with M. triplex was diagnosed. Except for the patient with pneumoconiosis, all other patients received different therapeutic regimens with variable duration (Table 1). Of these, one was cured, one improved slightly, one did not improve, and the last one was not reported. The presence of preexisting chronic obstructive pulmonary disease and kyphoscoliosis in our patient may have predisposed to the development of atypical mycobacterial infection. Prolonged quadruple treatment eventually eradicated the pathogens and at least stabilized the disease process.

CONCLUSION: M. triplex, an emerging pathogen, infrequently causes pulmonary disease in immunocompetent persons. Treatment with prolonged duration of combined chemotherapy was shown to be associated with reduced symptoms and good clinical outcome.

DISCLOSURE: Mingchen Song, No Financial Disclosure Information; No Product/Research Disclosure Information

REFERENCES

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