Application of Polymerase Chain Reaction Technique for Laboratory Diagnosis of Cutaneous Tuberculosis

Objective: Evaluation of the role of polymerase chain reaction (PCR) for the detection of Mycobacterium tuberculosis (MTB) DNA as a diagnostic aid in cutaneous tuberculosis. Study Design: Descriptive study. Duration and place of study: TB reference laboratory, PHLS, Ahvaz, Iran from May 2001 to December 2001. Patients & Methods: Thirty formalin-fixed, paraffin-embedded samples belonging to 28 patients were analyzed. Tissue sections were treated by lysis buffer containing proteinase K and DNA was extracted by using standard extraction kit. PCR amplification was performed using assay based on a repetitive sequence IS 6110 of MTB according to standard procedure. Results: PCR was positive in six samples. Amongst them, two of the samples (7.1%) belonged to patients with chronic granulomatosis, which was previously confirmed histopathologically, were positive in entire applied tests, i.e. direct smear, culture and PCR. Using PCR technique, six out of the total specimens tested (21.4%), were positive for the presence of M. tuberculosis DNA. Statistically the difference between applied methods was significant (P<0.0016). Accounting histopathology as gold standard, the sensitivity of PCR in this study was determined as 75%. Conclusions: Our study showed that from 8 cases of skin tuberculosis diagnosed by histopathology, 6 were positive by PCR technique, which shows the superiority of previous method to molecular technique. However, PCR assay has priority to conventional bacteriologic methods for detection of M. tuberculosis from cutaneous tuberculosis cases, and can be only used when the staining for acid fast bacilli is negative and there is a lack of growth on culture or when fresh material has not been collected for culture.