AB031. Pulmonary infection by mycobacterium malmoense

Abstract: An interesting case of pulmonary infection due to a rare non tuberculous mycobacterium is presented. A 61-year-old patient, smoker, with a history of diabetes melitensis, was referred to our clinic, because of acid-fast positive sputum examination probably from M. tuberculosis. He had weight loss of 6 kgr/2 months, loss of appetite, weakness and cough since 2 years. Two years ago his chest X-rays showed probable TB lesions but his bronchoscopy examination was negative. A chest CT examination revealed multiple cavitary and nodular lesions in both lungs. A skin test for TB was negative. Sputum stain (Ziehl-Neelsen) and cultures (Lowenstein-Jensen and MGIT) were positive for non-tuberculous mycobacterium, that later identified as M. malmoense. It was impossible to determine its drug susceptibility. The patient received INH, RIF, PZA, EMB initially and after two months PZA was stopped and clarithromycin was started based on the laboratory results. Sputum cultures were repeatedly negative after the second month of therapy. After 22 months on this treatment, he continues to suffer from easy fatigability while his X-rays show only little improvement. M. malmoense is a pathogenic slowly growing non tuberculous mycobacterium. It causes severe morbidity and mortality. It has been recovered from natural waters in northern Europe and soils in Zaire and Japan and rarely in USA. Main sources of infection are water, soil and dust. There is no human to human transmission. Men of middle age are most susceptible. The most common site of infection is respiratory system, especially in patients with COPD or post TB bronchiectasis. In children, it causes lymphadenitis. Rarely, it can affect the skin, the soft tissues and bones in immunocompromised patients. Our patient probably was exposed to M. malmoense during his duties as military officer in Northern Europe. He had undiagnosed COPD and he was not immunocompromised (HIV negative). The diagnosis of his illness was prompt following the results of sputum culture. His therapeutic regimen was modified accordingly. Pulmonary M. malmoense infection may be difficult to treat. The original isolates were reported as susceptible in vitro to ethambutol, ethionamide, kanamycin, and cycloserine, but resistant to INH, streptomycin, rifampin, and capreomycin. Several investigators have reported a lack of consistency and correlation between clinical response and in vitro antimicrobial susceptibilities among strains. The optimal chemotherapy is not known, but it is recommended to consist of combinations of INH, rifampin, and ethambutol, with and without quinolones and macrolides at least for 24 months. The prognosis is uncertain.

Keywords: Pulmonary infection; non-tuberculous mycobacterium; M. malmoense treatment