Nested polymerase chain reaction in the diagnosis of negative Ziehl-Neelsen stained Mycobacterium tuberculosis fistula-in-ano: report of four cases.

PURPOSE: Mycobacterium is one of the causes of granulomatous diseases within the anorectal region. Early diagnosis of infection is important before the use of antituberculosis chemotherapy. Clinical diagnosis is usually dependent on microscopic detection using Ziehl-Neelsen stain and mycobacterial culture, but the sensitivity and specificity of these two methods are low. In this study nested polymerase chain reaction was used to detect mycobacterial infection in anal fistulas.

METHODS: Paraffin-embedded specimens from three patients and discharge from one patient were used. DNA extraction was performed using phenol/chloroform techniques. IS6110-based nested polymerase chain reaction, yielding a 259-bp amplicon, for the diagnosis of infection was done to facilitate treatment.

RESULTS: Four cases of suspected fistulas-in-ano presented with persistent fistula or unhealed wound. Histopathologic examination revealed granulomatous inflammation with failed microscopic detection of acid-fast bacilli using Ziehl-Neelsen stain. Nested polymerase chain reaction confirmed the presence of in all cases. The anal lesions healed rapidly following a course of antituberculosis therapy.

CONCLUSION: Molecular diagnosis of fistula-in-ano by nested polymerase chain reaction is useful for clinically highly suspected infection despite a negative Ziehl-Neelsen stain.