Incidence of Mycobacterium tuberculosis detection in formalin fixed- paraffin embedded granulomatous dermatoses with Multiplex PCR comparing with fluorescent microscopy and acid fast staining in eastern Iran

Abstract

Introduction: Distinguishing cutaneous tuberculosis to from other granulomatous dermatoses is usually difficult. We used polymerase chain reaction (PCR) to evaluate the incidence of cutaneous tuberculosis and comparison of PCR with other conventional methods in formalin-fixed, paraffin-embedded tissues (FFPE) having unspecified granulomatous inflammation. Materials and Methods: A total of 30 consecutive specimens which had been collected from 30 different patients and fulfilled the criteria for tissues described above were used in this study. Samples obtained from skin biopsy archived blocks of Pathology Department of Ghaem Hospital-Mashhad, Islamic Republic of Iran from January 2000 to June 2003 . Two different primer pairs of MD1-MD2 and KD1-KD2 targeting the gene of of 162 bp (common to all mycobacteria) and of 123 bp DNA (specific for M. tuberculosis complex) were used in the PCR assays. Results: Of the 30 specimens, 6 were PCR positive for the 123 bp DNA. All of these 6 cases, were PCR positive for 162 bp DNA too. Cutaneous tuberculosis could be diagnosed in these 6 cases (20.0%).). After reviewing their clinical presentation, 5 cases were considered as lupus vulgaris. No cases was positive only for 162 bp gene.. There were 4 and 5 positive specimens in fluorescent and acid fast staining respectively. Conclusion: These results show that in cutaneous tuberculosis with unclassical clinical and histological presentation, PCR provides rapid and sensitive detection of M. tuberculosis DNA in FFPE specimens. In areas like Iran, where prevalence of extrapulmonary tuberculosis is still high, lupus vulgaris is common form of cutaneous tuberculosis and are seen more frequently than atypical mycobacterial infection. Finally, conventional methods of tissue staining have somewhat lower potency from PCR in distinguishing mycobacteria