Mycobacterium Xenopi Workup

Updated: Jul 07, 2017
  • Author: Mansoor Arif, MD; Chief Editor: Mark R Wallace, MD, FACP, FIDSA  more...
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Workup

Laboratory Studies

Serum electrolyte tests may reveal hyponatremia, most likely due to inappropriate secretion of antidiuretic hormone syndrome.

CBC counts may reveal leukocytosis, leucopenia, anemia, reactive thrombocytosis, or thrombocytopenia, or they may be entirely within reference ranges.

Mycobacterial examination of sputum, [6] blood, urine, bronchoalveolar lavage fluid, and tissue biopsies may reveal M xenopi.

American Thoracic Society criteria are used for diagnosing nontuberculous mycobacterial lung disease in HIV-seropositive or HIV-seronegative patients. Use the following criteria when diagnosing symptomatic patients who have infiltrative, nodular, or cavitary lung disease and those with high-resolution CT scan findings that reveal multifocal bronchiectasis and/or multiple small nodules:

  • If 3 sputum/bronchial wash results from the previous 12 months are available: Three positive culture findings with negative acid-fast bacilli (AFB) smear results or 2 positive culture findings and 1 positive smear result.
  • If only 1 bronchial wash result is available: Positive culture findings with a 2+, 3+, or 4+ AFB smear result or a 2+, 3+, or 4+ growth on solid media
  • If sputum/bronchial wash results are nondiagnostic or another disease cannot be excluded: Transbronchial or open lung biopsy yielding M xenopi or biopsy showing mycobacterial histopathologic features (granulomatous inflammation [7] or AFB) and 1 or more sputum or bronchial wash result positive, even in a low number, for M xenopi
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Imaging Studies

Chest radiography

The classic appearance of M xenopi is cavitary apical pulmonary disease. The cavities have thin walls with little surrounding parenchymal infiltration.

Bronchogenic spread of disease is rare and appears as patchy, irregular, alveolar or interstitial opacities.

Adenopathy and pleural effusions are rare and are not isolated findings.

The nonclassic form develops in about 25% of patients and appears as multiple patchy alveolar, interstitial pneumonitis, or interstitial opacities without defined borders (predominantly in the lower lung fields).

M xenopi may occasionally manifest as a solitary pulmonary nodule, usually in asymptomatic individuals who come to medical attention because of possible malignancy. Surgical resection demonstrates changes without evidence of tumor.

Chest CT scanning

This defines the features more precisely by possibly revealing bronchiectasis and 5- to 15-mm nodular opacities.

Carillo et al compared CT scan findings of M xenopi infection with those of Mycobacterium avium-intracellulare infection. In their patient population, they observed a more fibrocavitary and nodular pattern in patients with M xenopi infection compared to classic descriptions of it being more bronchiectatic. They also described findings consistent with ground-glass opacifications and consolidations. [8]

Positron emission tomography (PET)–CT imaging

This often reveals solitary pulmonary nodules that may mimic carcinoma.

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Procedures

See the list below:

  • Bronchoscopy with bronchoalveolar lavage
  • Bronchoscopy with endobronchial or transbronchial biopsies
  • Transbronchial needle aspiration
  • Video-assisted thoracoscopic biopsy
  • Open lung biopsy (rarely indicated)
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Histologic Findings

Necrotizing or non-necrotizing granulomatous inflammation is observed in lung biopsy samples.

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Staging

Similar to other nontuberculous mycobacteria

  • Presumed colonization
  • Localized disease (eg, in the lungs)
  • Disseminated disease or mycobacteremia
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