Pulmonary infections with atypical mycobacteria in the normal host

CT findings of pulmonary non-tuberculous mycobacterial infection in non-AIDS immunocompromised patients: a case-controlled comparison with immunocompetent patients

OBJECTIVE

To describe CT findings of non-tuberculous mycobacteria (NTM) pulmonary infection in non-AIDS immunocompromised patients (ICPs) and to compare these findings with those in immunocompetent patients.

METHODS

From July 2000 to August 2007, 369 patients (mean age 58.3 years; 169 males and 200 females) with pulmonary NTM infection were retrospectively reviewed. Of these 369 patients, 24 ICPs (mean age 64.8 years; 15 males and 9 females) were identified. 16 patients had diabetes mellitus, and 6 patients had received long-term steroid therapy. One had received solid organ transplantation and one had received high-dose chemotherapy for haematological disease. 24 age- and sex-matched immunocompetent patients (mean age 64.6 years; 15 males and 9 females) were selected as the control group from the same registry. CT images were reviewed in consensus by three chest radiologists, who were blinded to immune status. Each lung lobe was evaluated in terms of extent of the lesion, bronchiectasis, parenchymal opacity and the presence of ancillary findings. results: A total of 287 lobes were evaluated in ICPs and the control group. The ICPs showed a higher prevalence of ill-defined nodules, with cavities and large opacity >2 cm with/without cavity (p=0.03, 0.04 and 0.02, respectively). Regardless of the immune status, the most common CT findings were bronchiectasis and ill-defined nodules without cavity.

CONCLUSION

The most common CT findings of pulmonary NTM infection in ICPs were bronchiectasis and ill-defined nodules, similar to those in the control group. Ill-defined nodules with cavity and large opacity >2 cm with/without cavity were more frequently found in ICPs.

ADVANCES IN KNOWLEDGE

In patients affected by NTM infection, large opacities and cavitation in pulmonary nodules are more frequent in ICPs than in immunocompetent patients.

The Many Faces of Pulmonary Nontuberculous Mycobacterial Infection

OBJECTIVE

The purpose of this article is to review clinical and radiologic manifestations of pulmonary nontuberculous mycobacterial infection.

CONCLUSION

Common and well-recognized patterns of infection include cavitary and bronchiectatic disease and infection in AIDS patients. Less common or well-recognized manifestations include nodules or masses mimicking malignancy, hypersensitivity pneumonitis, and others. Definitive diagnosis can be difficult and patterns may overlap. Timely diagnosis requires a high index of suspicion and knowledge of the spectrum of clinical and radiologic features.

Imaging of Non-tuberculous (Atypical) Mycobacterial Pulmonary Infection

Pulmonary infections due to mycobacterial organisms are increasing in incidence. Non-tuberculous (atypical) mycobacteria (NTM) represent a significant proportion of mycobacterial infections and may prove difficult to diagnose due to their non-specific clinical and radiographic presentations. An increasing volume of radiological data is now available for the more common non-tuberculous mycobacterial infections, and we have summarized the imaging features found in such cases, identifying radiographic features that would favour the diagnosis of a non-tuberculous mycobacterium and that, in some cases, suggest a specific organism.

Pulmonary nontuberculous mycobacterial infection: radiologic manifestations

The nontuberculous mycobacteria (NTMB) are a group of bacteria that can infect the cervical lymph nodes, skin, soft tissues, and lung. Pulmonary NTMB disease is increasing in prevalence and is most commonly caused by Mycobacterium avium-intracellulare or M kansasii. Occasionally, M xenopi, M fortuitum, or M chelonae also causes pulmonary disease. Diagnosis of pulmonary NTMB infection is often difficult because isolation of the organism from sputum or bronchoalveolar lavage fluid can represent airway colonization. The radiologic manifestations of pulmonary NTMB infection are protean and include consolidation, cavitation, fibrosis, nodules, bronchiectasis, and adenopathy. Pulmonary NTMB infection has five distinct clinicoradiologic manifestations: (a) classic infection, (b) nonclassic infection, (c) nodules in asymptomatic patients, (d) infection in patients with achalasia, and (e) infection in immunocompromised patients. Although classic NTMB infection may be indistinguishable from active tuberculosis, it is usually more indolent. The radiologic features of nonclassic NTMB infection are characteristic: bronchiectasis and centrilobular nodules isolated to or most severe in the lingula and middle lobe. In patients with acquired immunodeficiency syndrome, mediastinal or hilar adenopathy is the most common radiographic finding. Knowledge of the full spectrum of clinical and radiologic features of pulmonary NTMB infection is important to facilitate diagnosis and treatment.

Rapidly growing mycobacterial lung infection in association with esophageal disorders

Esophageal or other swallowing disorders complicated by lipoid pneumonia are reported to be associated with pulmonary infections caused by rapidly growing mycobacteria. Herein we describe a 63-year-old woman with achalasia of the esophagus complicated by lung infection with Mycobacterium chelonae and a 47-year-old man in whom long-term ingestion of mineral oil was complicated by lipoid pneumonia and M. fortuitum lung infection. A MEDLINE search of English language publications from 1966 to 1997 revealed 18 cases of lung infections caused by rapidly growing mycobacteria in patients with esophageal disorders. Of these 18 patients and our 2 patients, 11 were men and 9 were women (mean age, 50 years). Achalasia was present in 11 patients, and 6 had lipoid pneumonia without evidence of esophageal disorders. Three patients had lipoid pneumonia caused by lipoid ingestion in the setting of achalasia or another swallowing disorder. In 14 patients, lung infection was caused by M. fortuitum; in 5, M. chelonae; and in 1, a non-M. fortuitum rapidly growing mycobacterial infection. The most common clinical feature was fever, and the most common roentgenologic abnormality was the presence of unilateral or bilateral and patchy or dense infiltrates. The sputum was the most common source of isolation of rapidly growing mycobacteria. Achalasia and lipoid pneumonia are important risk factors for the development of lung infections caused by rapidly growing mycobacteria. Treatment of the esophageal disease might prevent occurrence of and facilitate recovery from these infections.

Pulmonary infection with Mycobacterium avium-intracellulare leads to air trapping distal to the small airways

To clarify the structure and function of the airways in Mycobacterium avium-intracellulare (MAI) infection, we performed pulmonary function tests and high-resolution computed tomography (HRCT) of the thorax in female patients 61 +/- 9 yr of age (n = 12) with pulmonary MAI infection without predisposing lung disease and compared their data with those of normal female volunteers 54 +/- 8 yr of age (n = 9). We calculated the E/I ratio, i.e., the average ratio of HRCT number at full expiration to that at full inspiration, as an index for the evaluation of air trapping distal to the small airways. Patients showed significant increases in residual volume and slope of phase III (DeltaN2) of the single-breath nitrogen test, and significant decreases in flow at 50 and 25% of FVC, suggesting hyperinflation and obstruction of the small airways. HRCT of patients revealed the small nodules and ectasis of bronchioles and small bronchi located mainly in segments (S) S2, S3, S4, and S5. The E/I ratio was significantly elevated in patients, and especially higher in the upper lung field than in the lower lung field, suggesting air trapping distal to the small airways. The difference of E/I ratio between the upper and lower field is probably related to the segmental distribution of CT abnormalities. These findings suggest that MAI infection can lead to air trapping distal to the small airways.

PCR assay based on DNA coding for 16S rRNA for detection and identification of mycobacteria in clinical samples

A PCR and a reverse cross blot hybridization assay were developed for the detection and identification of mycobacteria in clinical samples. The PCR amplifies a part of the DNA coding for 16S rRNA with a set of primers that is specific for the genus Mycobacterium and that flanks species-specific sequences within the genes coding for 16S rRNA. The PCR product is analyzed in a reverse cross blot hybridization assay with probes specific for M. tuberculosis complex (pTub1), M. avium (pAvi3), M. intracellulare (pInt5 and pInt7), M. kansasii complex-M. scrofulaceum complex (pKan1), M. xenopi (pXen1), M. fortuitum (pFor1), M. smegmatis (pSme1), and Mycobacterium spp. (pMyc5a). The PCR assay can detect 10 fg of DNA, the equivalent of two mycobacteria. The specificities of the probes were tested with 108 mycobacterial strains (33 species) and 31 nonmycobacterial strains (of 17 genera). The probes pAvi3, pInt5, pInt7, pKan1, pXen1, and pMyc5a were specific. With probes pTub1, pFor1, and pSme1, slight cross hybridization occurred. However, the mycobacterial strains from which the cross-hybridizing PCR products were derived belonged to nonpathogenic or nonopportunistic species which do not occur in clinical samples. The test was used on 31 different clinical specimens obtained from patients suspected of having mycobacterial disease, including a patient with a double mycobacterial infection. The samples included sputum, bronchoalveolar lavage, tissue biopsy samples, cerebrospinal fluid, pus, peritoneal fluid, pleural fluid, and blood. The results of the PCR assay agreed with those of conventional identification methods or with clinical data, showing that the test can be used for the direct and rapid detection and identification of mycobacteria in clinical samples.