Role of polymerase chain reaction in the diagnosis of cutaneous tuberculosis

Objective This study was designed to establish polymerase chain reaction (PCR) as a more effective tool for diagnose cutaneous tuberculosis (TB). Methods This cross-sectional study was conducted in the department of Dermatology u0026 Venereology, Bangabandhu Sheikh Mujib Medical University (BSMMU), Dhaka, Bangladesh, over a duration of one year. Thirty clinically diagnosed patients of cutaneous tuberculosis were selected for this study. The selected skin lesion was biopsied and it was divided in two portions, one for histopathological examination and another for bacteriological Ziehl-Neelsen (Z-N) staining, culture and molecular PCR analysis. Results In our study mean age was found 34.5±16.6 years, male to female ratio was 1.3:1. Tuberculosis verrucosa cutis (43%) was the commonest type of skin TB than lupus vulgaris (30%), erythema induratum of Bazin (13.3%) and others cutaneous types (13.3%). Concomitant pulmonary tuberculosis was detected in 10% of examined patients. In histopathological report, maximum 22 (73.3%) samples had typical granuloma without caseous necrosis, 5 (16.7%) cases had granuloma with caseous necrosis and 3 (10.0%) had only inflammatory cell infiltrate. Mantoux test was positive in 76.7% of the cutaneous tuberculosis patients. The evidence of Mycobacterium tuberculosis was negative in microscopy and culture media. PCR was positive in 3 (10.0%) patients. Sensitivity and specificity of PCR for M . tuberculosis was determined as 7.4% and 66.7%, respectively. Accuracy was found 13.3% whereas positive predictive value and negative predictive value were found 66.7% and 7.4% respectively. Conclusion Although higher specificity of cutaneous tuberculosis cases, the low sensitivity of PCR in this study, discourages the use of this method in routine diagnosis of cutaneous tuberculosis .