Histologic parameters predictive of mycobacterial infection.

Tissue specimens from a wide variety of anatomic locations are frequently examined for mycobacteria using a combination of cultures and special stains. Auramine-rhodamine (AR) staining is a sensitive method for detecting acid-fast bacilli (AFB) in tissue sections. We reviewed 85 AR-positive and 275 randomly selected AR-negative biopsy specimens collected during the past 2 years at the Mayo Clinic, Rochester, Minn. Pathologic diagnoses and culture results were also reviewed. Biopsy specimens containing necrotizing granulomas yielded the highest positivity rate for AFB (61 [47.7%]), followed by nonnecrotizing granulomas (14 [17.7%]). Poorly formed granulomas (5 [16.1%]) and acute inflammation (5 [15.6%]) were less frequently positive. Cases with fibrotic or hyalinized granulomas, nonspecific chronic inflammation, nonspecific reactive or reparative changes, no significant histologic abnormality, or malignancy failed to disclose AFB. These specimens, which were consistently negative for AFB, were responsible for 25% of the samples submitted. Of the 360 tissue specimens submitted, 166 had a corresponding mycobacterial culture. Mycobacteria were cultured only from the biopsy specimens that contained necrotizing granulomas (38.2%), nonnecrotizing granulomas (32.4%), poorly formed granulomas (30.0%), or acute inflammation (15.8%). Tissues with fibrotic or hyalinized granulomas, nonspecific chronic inflammation, nonspecific reactive or reparative changes, no significant histologic abnormality, or malignancy failed to yield positive cultures. These data suggest that biopsy specimens with these latter diagnoses are inappropriate specimens for mycobacterial culture or AR staining.