RESUMO
Background: The microbiologic diagnosis of cutaneous tuberculosis is difficult because most lesions harbor only a small number of mycobacteria that cannot usually be detected by staining for the organism or by culture. Nucleic acid amplification tests based on the polymerase chain reaction (PCR) are potentially useful in this situation. Aims: To evaluate the utility of mRNA PCR and DNA PCR in the diagnosis of cutaneous tuberculosis. Methods: Biopsies from 28 cases of cutaneous tuberculosis and 19 controls with other diseases were subjected to microbiologic tests including direct smears for mycobacteria, culture and both mRNA PCR and DNA PCR. The laboratory was blinded to the clinical diagnosis. Results: None of the patients or controls showed a positive reaction on mRNA PCR test. Seven of 28 cases and 5 out of 19 controls showed a positive result on DNA PCR test yielding a sensitivity of 25% and a specificity of 73.7%. Conclusion: The results of PCR tests in cutaneous tuberculosis should be interpreted in the light of clinical and histopathological findings.