Mycobacterium Kansasii Workup

• Diagnosis of M kansasii infection requires isolation of the organism. Unlike other nontuberculous mycobacteria (NTM), M kansasii is believed to rarely represent colonization or an environmental contaminant.
• Initially, evaluate at least 3 sputum samples by AFB staining and mycobacterial cultures. Bacteriologic examination may include AFB stain and culture of specimens (eg, bronchoalveolar lavage, aspirates from sterile sites, tissues).
• Blood culture may be useful to detect M kansasii bacteremia and to establish a diagnosis of disseminated infection. Approximately 10% of patients with HIV infection who are also infected with M kansasii have blood cultures positive for M kansasii.
• Nucleic acid probes and polymerase chain reaction (PCR) are useful for early identification of growing M kansasii colonies. They are highly sensitive and specific, providing species identification using a culture directly from BACTEC broth within 2-4 hours.
• Susceptibility testing: The Clinical and Laboratory Standards Institute (CLSI) recommends that all initial isolates of M kansasii be tested only for rifampin susceptibility.^[9] Rifampin-susceptible isolates are also susceptible to rifabutin. If the isolate is resistant to rifampin, further susceptibility to rifabutin, isoniazid, streptomycin, clarithromycin, amikacin, ethambutol, trimethoprim-sulfamethoxazole, ciprofloxacin, moxifloxacin, and gatifloxacin should be determined. Rifampin-resistant isolates should be sent to an experienced reference laboratory for further testing.^[10] Ciprofloxacin susceptibility results mirror those of susceptibility for both ofloxacin and levofloxacin.
• Interpretation of isoniazid susceptibility may be confusing because most M kansasii organisms show resistance to IN isoniazid H at 1 mcg/mL but are susceptible at 5 mcg/mL. The latter reflects a better correlation with in vivo isoniazid activity.
• The currently available skin test is not helpful in establishing diagnosis.

Approximately 90% of patients with M kansasii disease have cavitary infiltrates on chest radiography, as depicted below. Among patients without cavitary lung lesions, clinical symptoms and high-resolution computed tomography (HRCT) scanning are important adjuncts in defining the presence of lung disease.

The characteristic radiological feature of M kansasii pulmonary infection has been described as a right-sided, apical or subapical, thin-walled cavitary infiltrate.^[6] In a separate study, which included only patients without HIV infection, a comparison of chest radiography findings in patients with M kansasii infection with those in patients with tuberculosis showed that M kansasii infection occurred more frequently as unilateral, right-sided infiltrates. Cavities were observed in both cases, whereas pleural effusions and air space shadowing involving multiple bronchopulmonary segments were less common in M kansasii infection.^[5]

Analysis of chest radiographs in a series of 16 patients infected with HIV and M kansasii pulmonary infection showed the following abnormalities (in decreasing order of frequency):

1. Alveolar opacities
2. Cavity
3. Thoracic lymphadenopathy
4. Pleural effusions
5. Interstitial opacities

• Baseline laboratory workup for M kansasii infection should include complete blood cell count (CBC), renal profile, and liver profile.
• Patients with M kansasii infection should be counseled about HIV infection and tested for HIV infection.
• Perform a complete HIV evaluation if the patient tests positive for HIV. This evaluation should include CD4 counts and HIV viral load.

• Bronchoscopy, tissue biopsy, thoracentesis, or pericardiocentesis may be needed to recover the pathogen and establish diagnosis. In some cases, transthoracic needle aspiration or open-lung biopsy may be necessary.
• Bone marrow and liver biopsies may be useful in establishing disseminated M kansasii infection.
• Needle aspiration or biopsy of a skin lesion (eg, nodule) may be useful for establishing M kansasii skin infections.^[2]

The variable histopathologic findings of M kansasii disease may include acute suppuration, nonnecrotic tubercles, or caseation. In general, the findings are similar to tuberculosis.

Examination of lung tissue and lymph nodes usually shows caseating granulomas. Skin lesions may show granulomas with areas of necrosis or foci of acute and chronic inflammation without well-formed granulomas. Other tissues may show caseating or noncaseating granulomas.

AFB are commonly seen in tissues from lungs and lymph nodes. They are found less commonly in tissues from other sites.

In patients with AIDS or other immunocompromised states, many of the histologic characteristics usually associated with M kansasii infection may be absent. Cytologic and histologic material may show a wide range of inflammatory reactions, including granulomas with and without necrosis, neutrophilic abscesses, spindle-cell proliferation, and focal granular eosinophilic necrosis.^[11]

Diagnostic criteria based on American Thoracic Society/Infectious Disease Society of America Guidelines

In 1997, the American Thoracic Society (ATS) established diagnostic criteria for NTM lung disease, regardless of the host's HIV status.^[12] These guidelines were revised and approved by the American Thoracic Society and Infectious Disease Society of America (IDSA) in 2007.

M kansasii is considered a highly pathogenic mycobacterium, and many experts advise that M kansasii isolated from lungs or elsewhere almost always warrants treatment, especially in patients with HIV/AIDS and in other immunocompromised groups. The authors of the ATS/IDSA guidelines also acknowledge and suggest that the treatment decisions for M kansasii should be made carefully, even if some specimens are not positive for M kansasii or if multiple specimens are not available, and they recommend expert consultation in the decision-making process.

The general diagnostic criteria for all NTM pulmonary infections based on 2007 ATS/IDSA guidelines are summarized below.^[13]

Clinical criteria

Both of the following clinical criteria are required to establish a diagnosis of NTM lung disease:

• Pulmonary symptoms, nodular or cavitary opacities on chest radiography, or a HRCT scan that shows multifocal bronchiectasis with multiple small nodules
• Appropriate exclusion of other diagnoses

Microbiologic criteria

One of the following microbiologic criteria is required for diagnosis of NTM lung disease:

• Positive culture results from at least 2 separate expectorated sputum samples (If these culture results are nondiagnostic, consider repeat sputum AFB smears and cultures.)
• Positive culture result from at least one bronchial wash or lavage
• Transbronchial or other lung biopsy sample with mycobacterial histopathologic features (granulomatous inflammation or AFB) and positive culture for NTM; alternatively, a biopsy sample showing mycobacterial histopathologic features (granulomatous inflammation or AFB) and one or more sputum or bronchial washings that are culture-positive for NTM

The ATS/IDSA guideline also recommends the followings for diagnosis:

• Expert consultation should be obtained when NTM that are either infrequently encountered or that usually represent environmental contamination are recovered.
• Patients with suspected NTM lung disease but who do not meet the diagnostic criteria should be observed until the diagnosis is firmly established or excluded.
• A diagnosis of NTM lung disease does not automatically necessitate the institution of therapy, which is a decision based on potential risks and benefits of therapy in individual patients.