Chest computed tomography predicts microbiological burden and symptoms in pulmonary Mycobacterium xenopi

The development of computed tomography (CT) findings usually precedes the diagnosis of pulmonary nontuberculous mycobacterial infection. The utility of specific CT scan features, although often available long before respiratory sample cultures, is not fully understood. We sought to assess associations among CT features, symptoms and microbiological disease criteria in pulmonary Mycobacterium xenopi isolation.

We reviewed 70 consecutive immunocompetent patients with pulmonary M. xenopi isolation and classified them according to the American Thoracic Society (ATS) diagnostic criteria for disease. 'Definite disease' patients (n = 16) met modified ATS criteria. 'Possible disease' patients (n = 10) met microbiological criteria, had abnormal CT scans, but data regarding symptoms were unavailable. 'No disease' patients (n = 44) had only one positive sputum culture, or were asymptomatic or had no relevant CT findings. Two radiologists, without knowledge of the clinical or microbiological information, independently reviewed the scans.

The mean (standard deviation) age of all patients was 63 (16) years, and 39% were women. Patients with 'definite disease' usually had nodules (88%) and cavities (63%), but less often bronchiectasis (50%) and tree-in-bud (50%). Patients with 'possible' or 'no disease', respectively, had nodules (100% or 80%), bronchiectasis (40% or 18%) or tree-in-bud (40% or 11%). Cavitation (P ≤ 0.0001) and nodules ≥ 5 mm (P = 0.0002) were associated with fulfilled microbiological criteria for disease. Bronchiectasis (P = 0.02) and nodules <5 mm (P = 0.002) were associated with symptoms of infection.

Among immunocompetent patients with pulmonary M. xenopi isolation, cavitation and large nodules predict fulfilling microbiological disease criteria, while bronchiectasis and small nodules predict symptoms.