Pitfalls

• For species-specific diagnosis, culture is necessary.

• Treatment should be modified to the specific species.

without evidence of bone involvement (Fig. 11—2). The mass was homogeneous and had a signal intensity consistent with soft tissue.

Differential Diagnosis

Neoplasm Fungal infection Mycobacterial infection Bacterial infection

Diagnosis

Microbacterial Infection

The diagnosis was a horseshoe abscess of noncaseating granulomatous disease secondary to mycobacteria other than tuberculosis (MOTT). Cultures were positive for Mycobacterium avium-intracellulare complex.

A major cause of granulomatous infections is mycobacteria. Two of the earliest identified mycobacteria were Mycobacterium tuberculosis and Mycobacterium leprae. Tuberculosis remains the most common pathologic organism of this genus. Hansen's disease or M. leprae has long been recognized as a separate species, but leprosy is far less common in most parts of the United States than some of the more newly recognized species. "Atypical mycobacteria" has traditionally meant a mycobacterium that is neither tuberculosis nor leprosy. An increased understanding of all nontuberculosis infections has led to the introduction of the term mycobacteria other than tuberculosis

Timpe and Runyon first showed MOTT to be pathogenic in humans in 1954. The Runyon classification system has been used to delineate species on the basis of pigment production or growth rate in culture. Runyon groups I, III, and IV have been identified as pathogenic in humans.

Mycobacteria may be identified immediately with acid-fast stain, but most often, as in this case, MOTT is not seen. Current microbiologic methods may take 8 to 10

Essentials of Human Physiology

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