Diagnosis of anorectal tuberculosis by polymerase chain reaction, GeneXpert and histopathology in 1336 samples in 776 anal fistula patients

BACKGROUND The association of tuberculosis (TB) with anal fistulas can make its treatment quite difficult. The main challenge is timely detection of TB in anal fistulas and its proper management. There is little data available on diagnosis and management of TB in anal fistulas. AIM To detect TB in fistula-in-ano patients were analyzed in different methods utilized. METHODS A retrospective analysis of different methods, polymerase chain-reaction (PCR), GeneXpert and histopathology (HPE), utilized to detect tuberculosis in fistula-in-ano patients, treated between 2014-2020, was performed. The sampling was done for tissue (fistula tract lining) and pus (when available). The detection rate of various tests to detect TB and prevalence rate of TB in simple vs complex fistulae were studied. RESULTS In 1336 samples (776 patients) tested, TB was detected in 133 samples (122 patients). TB was detected in 52/703 (7.4%) samples tested by PCR-tissue, in 77/331 (23.2%) samples tested by PCR-pus, 3/197 (1.5%) samples tested with HPE-tissue and 1/105 (0.9%) samples tested by GeneXpert. To detect TB, PCR-tissue was significantly better than HPE-tissue (52/703 vs 3/197 respectively) (P = 0.0012, significant, Fisher's exact test) and PCR-pus was significantly better than PCR-tissue (77/331 vs 52/703 respectively) (P < 0.00001, significant, Fisher's exact test). TB fistulas were more complex than non-tuberculous fistulas [78/113 (69%) vs 278/727 (44.3%) respectively] (P < 0.00001, significant, Fisher's exact test) but the overall healing rate was similar in tuberculous and non-tuberculous fistula groups [90/102 (88.2%) vs 518/556 (93.2%) respectively] (P = 0.10, not significant, Fisher's exact test). CONCLUSION This is the largest study of anorectal TB to be published. The detection of TB by polymerase chain-reaction was significantly higher than by histopathology and GeneXpert. Amongst polymerase chain-reaction, pus had a higher detection rate than tissue. TB fistulas were more complex than non-tuberculous fistulas but aggressive diagnosis and meticulous treatment led to comparable overall success rates in both groups.