Comparative Evaluation of Molecular Tests Vis-à-Vis Culture and Treatment Response in the Diagnosis of Cutaneous Tuberculosis.

The clinical diagnosis of cutaneous tuberculosis (CT) was based on criteria of reinfection and reactivation. Laboratory tests are mandatory but have limitations, thus demanding continuous innovation. In our study, we took punch biopsies from lesions on 48 patients. Half of these biopsies underwent histopathologic investigation, and the other half were analysed using the BACT Alert 3D system, the Amplified Mycobacterium Tuberculosis Direct Test (AMTDT), and DNA amplification by polymerase chain reaction (PCR) using primers specific for the M. tuberculosis 16SrRNA complex. Patients were given antitubercular therapy for 6 weeks. A positive response was indicative of CT. Histopathology was suggestive, although no acid-fast bacilli could be demonstrated. In vitro culture recovery of M. tuberculosis was possible in six (12.5%); only two (4%) were positive on AMTDT, and 14 (29%) on real-time PCR. Regression of skin lesions was remarkable after antitubercular therapy, irrespective of a laboratory result. AMTDT and real-time PCR are seen to be of low value in the diagnosis of CT. They are limited by high cost, their paucibacillary nature, and technical errors. On comparing has AMTDT and PCR, the latter was found to be superior. High percentages of negative results were also investigated; extensive involvement of skin has yielded positive PCR results, probably due to low immunity and high bacterial load.