OBJECTIVES: Ancillary molecular testing on tissue is available for mycobacterial disease; however, judicious use of highly sensitive tests, such as polymerase chain reaction (PCR) and sequencing, should be guided by histologic parameters. We sought to investigate the utility of performing acid-fast stains (AFS) on skin biopsy specimens with granulomatous inflammation without an otherwise obvious histologic or clinical explanation. METHODS: Our retrospective review identified 31 patients with biopsy specimens showing granulomatous inflammation that had simultaneous AFS and mycobacterial culture or PCR performed. RESULTS: Biopsy specimens from eight (25.8%) patients had AFS interpreted as positive or suspicious for acid-fast bacilli. Eight had positive cultures and one had positive PCR. One biopsy specimen with AFS that showed occasional acid-fast structures that were interpreted as "suspicious" for mycobacteria was associated with a negative culture and negative PCR. Three (9.7%) biopsy specimens with negative AFS had positive cultures, and 19 (61.3%) biopsy specimens with negative AFS also had negative culture results. In our biopsy specimens, sensitivity of AFS was 72.7% and specificity was 95.0%. Positive predictive value of AFS was 88.9%, and negative predictive value was 86.4%. CONCLUSIONS: AFS has good sensitivity and excellent specificity and should be performed on all unexplained granulomatous tissue reactions of skin in conjunction with mycobacterial culture.
OBJECTIVES: Ancillary molecular testing on tissue is available for mycobacterial disease; however, judicious use of highly sensitive tests, such as polymerase chain reaction (PCR) and sequencing, should be guided by histologic parameters. We sought to investigate the utility of performing acid-fast stains (AFS) on skin biopsy specimens with granulomatous inflammation without an otherwise obvious histologic or clinical explanation. METHODS: Our retrospective review identified 31 patients with biopsy specimens showing granulomatous inflammation that had simultaneous AFS and mycobacterial culture or PCR performed. RESULTS: Biopsy specimens from eight (25.8%) patients had AFS interpreted as positive or suspicious for acid-fast bacilli. Eight had positive cultures and one had positive PCR. One biopsy specimen with AFS that showed occasional acid-fast structures that were interpreted as "suspicious" for mycobacteria was associated with a negative culture and negative PCR. Three (9.7%) biopsy specimens with negative AFS had positive cultures, and 19 (61.3%) biopsy specimens with negative AFS also had negative culture results. In our biopsy specimens, sensitivity of AFS was 72.7% and specificity was 95.0%. Positive predictive value of AFS was 88.9%, and negative predictive value was 86.4%. CONCLUSIONS:AFS has good sensitivity and excellent specificity and should be performed on all unexplained granulomatous tissue reactions of skin in conjunction with mycobacterial culture.