Nontuberculous%20mycobacterial%20disease Diagnosis

Diagnosis

Hypersensitivity-like Disease

Nontuberculous mycobacterial (NTM) pulmonary disease syndrome presenting like a hypersensitivity lung disease
One form of this syndrome is the “hot tub lung” which is associated w/ MAC exposure
Another form of this syndrome similar to hypersensitivity-like pneumonitis is associated w/ occupational exposures to metalworking fluids
- Similar to “hot tub lung” but solely caused by M immunogenum

Evaluation

The following are criteria used to diagnose NTM Pulmonary Disease:

Clinical, radiographic & microbiologic criteria must all be met

Clinical

Signs & symptoms consistent w/ nontuberculous mycobacterium (NTM) pulmonary disease, &
Appropriate exclusion of other diagnoses (eg pulmonary TB, cancer)

Radiographic

Nodular or cavitary opacities on chest radiograph, or
In the absence of cavitations, high-resolution computed tomography (HRCT) scan that shows multifocal bronchiectasis & multiple small (noncalcified) nodules

Microbiologic

≥2 positive culture results from separate expectorated sputum samples, or
≥1 positive culture bronchial wash or lavage, or
Transbronchial or other lung biopsy w/ mycobacterial histopathologic features (granulomatous formation or acid-fast stain) & positive culture for NTM, or biopsy w/ mycobacterial histopathologic features (granulomatous formation or acid-fast stain) & ≥1 sputum or bronchial wash/lavage culture positive for NTM

Physical Examination

May reflect underlying lung pathology
Chest auscultation may reveal rhonchi, crackles, wheezes
Characteristic body morphotype is noted especially in nodular/bronchiectatic M avium complex (MAC) pulmonary disease

Laboratory Tests

Sputum Exam for Acid-Fast Bacilli (AFB)

Preferably 3 early-morning sputum specimens must be collected on separate days
Fluorochrome technique is the recommended method
If rapidly growing mycobacteria (RGM) is suspected, it is advised to use weaker decolorizing process
Semiquantitative analysis may be useful in the diagnosis

Bronchoscopy

Considered in patients who are unable to produce sputum
May be done w/ or w/o lung biopsy

Sputum Culture

All cultures should include both solid & liquid (broth) media
Liquid media produce rapid results & have higher yield of mycobacteria
Advantages of solid media are the following: Allow recognition of mixed infections, observation of colony morphology & growth rates, quantitation of organism, & serve as a substitute when liquid media cultures are contaminated
Quantitation of the number of colonies is recommended

Lung Biopsy

May be done in patients w/ nondiagnostic radiographic & microbiologic findings, or if there is concern on the presence of other disease causing radiographic abnormalities

Antimicrobial Susceptibility Testing

Clarithromycin susceptibility testing is recommended for MAC isolates
M kansasii strains are tested for Rifampin; strains that are susceptible to Rifampin will also be susceptible to Rifabutin
- Strains that are resistant to Rifampin should be tested against a panel of ancillary antimicrobials (eg Ethambutol, Isoniazid, Clarithromycin, Amikacin, fluoroquinolones, & sulfonamides)
- Testing for M terrae-M nonchromogenicum group, M simiae, M szulgia, & M celatum are the same as w/ M kansasii strains
- M xenopi testing is the same as M kansasii, but w/ the temperature adjusted to 42-45^oC
- M malmoense testing is the same as M kansasii, but w/ the pH adjusted to pH 6
Susceptibility testing for RGM (eg M fortuitum, M abscessus & M chelonae) includes Amikacin, Doxycycline, fluoroquinolones, sulfonamide or Co-trimoxazole, Cefoxitin, Clarithromycin, Linezolid, Tobramycin (for M chelonae), & Imipenem (for M fortuitum)
- M fortuitum group is easily identified by using Polymixin-B or sulfonamides
- Testing w/ Cefoxitin or Tobramycin is useful in identifying presence of M abscessus & M chelonae
Susceptibility testing for fastidious slow growing NTM is limited
- M haemophilum are tested using hemin or ferric ammonium citrate in 28-30^oC temperatures
- M genavense are tested in a macrobroth system incubated for >6 weeks; M ulcerans for 4-6 weeks at 30^oC

Other Laboratory Tests

Rapid species identification of NTM should be routinely done through DNA probes & high-performance liquid chromatography (HPLC)
RGM (especially M chelonae, M abscessus & M fortuitum) isolates should be identified using extended antibiotic in vitro susceptibility testing, DNA sequencing, or polymerase chain reaction (PCR) restriction endonuclease assay (PRA)
Baseline tests are necessary to assist in monitoring for efficacy & adverse effects of antimicrobial drugs & for the development of drug resistance
Request for complete blood count, renal function, liver function tests (LFT) prior to initiation of drugs
Testing for visual acuity, red-green color discrimination & hearing are advised at baseline

Baseline Laboratory Evaluations

Baseline tests are necessary to assist in monitoring for efficacy & adverse effects of antimicrobial drugs & forthe development of drug resistance
Request for complete blood count, renal function, liver function tests (LFT) prior to initiation of drugs
Testing for visual acuity, red-green color discrimination & hearing are advised at baseline

Imaging

Findings depend on whether the pulmonary disease is characterized by nodules & bronchiectasis (nodular/bronchiectatic disease) or predominantly fibrocavitary (similar to TB)
Plain chest X-ray may be adequate to evaluate fibrocavitary lung disease, whereas HRCT of the chest is recommended to evaluate nodular/bronchiectatic pulmonary disease
Findings on hypersensitivity-like pulmonary disease may include ground glass opacities as well as mosaic pattern as noted on HRCT scan

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