mon slow-growing mycobacteria (SGM) such as
Mycobacterium kansasii and MAC.
CASE PATIENT 1
INITIAL PRESENTATION AND EVALUATION
A 67-year-old man who is a smoker with
a past history of M. tuberculosis infection
treated in the 1970s presents to the emergency
department with cough and shortness of breath.
Physical examination reveals a thin man with hyperresonance on lung examination and crackles
in the left apex. Chest radiograph reveals an old
M. tuberculosis scar with fibrocystic disease and
a cavitary opacity in the left upper lobe (Figure
1). Pulmonary function tests document moderate
obstructive airway dysfunction. HIV test is negative. Sputum smears are positive for acid-fast bacilli. Culture determines that the organism is not M.
tuberculosis, and repeat cultures identify moderate
growth of M. kansasii.
APPROACH TO DIAGNOSIS
The diagnosis of NTM disease is very complex
and at times confusing. It should be based on
clinical, radiologic, and mycobacterial correlation
with good communication between the experts
in this field. The ATS/IDSA criteria for diagnosing NTM lung disease are shown in the Table. 9
These criteria best apply to MAC, M. kansasii, and
Mycobacterium abscessus but are clinically applied
to other NTM respiratory pathogens. Because of
the nonspecific symptoms and lack of diagnostic
specificity of chest imaging, the diagnosis of NTM
lung disease requires microbiologic confirmation.
Specimens sent to the laboratory for identifica-
tion of NTM must be handled with care to prevent
contamination and false-positive results. Transport
media and preservatives should be avoided, and
transportation of the specimens should be prompt.
These measures will prevent bacterial overgrowth.
Furthermore, the yield of NTM may be affected if
the patient has used antibiotics, such as macrolides and fluoroquinolones, prior to obtaining the
NTM should be identified at the species level. 9
The preferred staining procedure in the laboratory
is the fluorochrome method. Specimens should
be cultured on both liquid and solid media. Some
species require special growth conditions and/or
lower incubation temperatures, and other identification methods may have to be employed, such
as DNA probes, polymerase chain reaction genotyping, nucleic acid sequence determination, and
high-performance liquid chromatography. Species-specific skin test antigens are not commercially
available and are not helpful in the diagnosis
of NTM disease because of cross-reactivity of
M. tuberculosis and some NTM. However, increased prevalence of NTM sensitization based on
Figure 1. Chest radiograph demonstrating an old Mycobacterium
tuberculosis scar with fibrocystic disease and a cavitary opacity
in the left upper lobe.