Atypical Mycobacterial Infection Workup

Updated: Sep 22, 2023
  • Author: Arry Dieudonne, MD; Chief Editor: Russell W Steele, MD  more...
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Laboratory Studies

Organisms from blood, biopsy material, bone marrow, and stools grow on routine bacterial media, but growth is best achieved using selective mycobacterial media, such as a Lowenstein-Jensen medium or Middlebrook 7K10 and 7K11 agar. [26, 78]

Nucleic acid hybridization probes using target sequences or ribosomal RNA are available for rapid identification of clinical isolates. [27]

Species can be identified using high-performance liquid chromatography or biochemical tests.

Polymerase chain reaction (PCR)-restriction analysis of clinical isolates have been used for the identification of M kansasii. [79]

Disseminated M avium complex (MAC) disease is most commonly diagnosed using culture of blood and bone marrow or other normally sterile tissues or body fluids. Other ancillary studies, such as acid-fast bacilli smear or radiographic imaging of the abdomen or mediastinum for detection of lymphadenopathy, may provide supportive diagnosis information.


Imaging Studies

In patients without AIDS, the classic radiographic picture of the chest mimics reactivation tuberculosis. A second presentation includes the presence of patchy nodular infiltrates, without cavities in a nodular distribution. [55] Those features are mostly observed in adults with chronic bronchitis and emphysema. Evidence of bronchiectasis is detectable on CT scanning. [80, 81]

Multiple enlarged retroperitoneal and mesenteric lymph nodes can be observed on CT scanning of the abdomen.

Large bulky adenopathy may be observed on autopsy findings.

Some experts recommend fine-needle percutaneous aspiration to confirm the diagnosis. [82]



Bone marrow aspirate, when biopsy is performed, may show hypocellularity and presence of foamy histiocytes.

Acid-fast stain and culture of bone marrow specimen may reveal the presence of MAC.


Histologic Findings

The histologic findings associated with MAC vary considerably and range from granulomas to nodular foam cell lesions to purulent and necrotizing inflammations. [83] In 1994, Torriani et al studied a retrospective cohort of 44 AIDS patients with MAC bacteremia and complete autopsies over a period of 4 years. [84] They found that 30% had no histologic evidence of MAC. In the remaining 70%, reticuloendothelial and gastrointestinal involvement was most common. However, the number and distribution of involved sites was variable. Derived from this study's findings, MAC bacteremia may precede widespread tissue disease, and the risk of development of detectable histologic involvement was related to the duration of bacteremia. [84]