Comparison of histopathology, acid fast bacillus smear and real-time polymerase chain reaction for detection of Mycobacterium tuberculosis in anal fistula in 161 patients: A prospective controlled trial.

OBJECTIVE/BACKGROUND: Mycobacterium tuberculosis (MTB) is a known cause of refractory and recurrent fistula-in-ano. Histopathology of fistula tract and acid fast bacillus (AFB) smear of the pus are the standard procedures employed to diagnose MTB. However, they have some drawbacks. Nontubercular mycobacteria (NTM) has also been detected to cause fistula-in-ano and these methods cannot differentiate between MTB and NTM. Secondly, as these methods have low sensitivity, they could possibly be missing out MTB patients. Real-time polymerase chain reaction (RT-PCR) has high sensitivity in detecting mycobacteria. The aim of the study was to compare the sensitivity of RT-PCR, histopathology, and AFB smear in detecting MTB in fistula-in-ano.

METHODS: The histopathology and RT-PCR of tissue (fistula tract) was done along with AFB smear and RT-PCR of the pus was done in all the cases as per the availability of the specimen. The histopathology, AFB smear and RT-PCR was done by same pathologists in all the cases and all the patients were operated by a single surgeon.

RESULTS: A total of 286 samples were tested in 161 patients of fistula-in-ano who were operated over a period of 1year. The mean age was 38.6±10.5 and male/female ratio was 153/8. Histopathology and RT-PCR of tissue (fistula tract) was done in 131 patients and 141 patients respectively. AFB smear and RT-PCR of pus (fistula) was done in 14 patients. Overall, MTB was detected in total of 17/161 (10.63%) patients. Out of these, MTB was detected in tissue (fistula tract) in 1/131 (0.76%) by histopathology and 14/141 (10%) by RT-PCR tissue. In pus samples, AFB smear was negative in all cases (0/14), whereas RT-PCR detected MTB in four of 14 (28.6%) patients. In 17 patients detected to have MTB, four-drug antitubercular therapy (ATT) was recommended. ATT was started in 15 patients. Nine of 17 patients completed 6months ATT and were cured. Six of 17 patients are currently taking ATT. Two patients did not take ATT; both of these have persistent symptoms of pus formation. Out of nine cured patients, two patients did not start ATT for 2months after detection. Only after the symptoms (persistent pus discharge) continued, did they start ATT and were subsequently cured.

CONCLUSION: RT-PCR is significantly more sensitive than histopathology and AFB smear in detecting MTB in fistula-in-ano. The routine practice of doing only histopathology and AFB smear in fistula patients might be missing a significant number of MTB cases and could be responsible for many recurrences in fistula patients. RT-PCR should preferably be done in all fistula cases and at least in refractory and recurrent fistulas.