Performances of single tube nested polymerase chain reaction and GeneXpert ultra on Formalin fixed paraffin embedded tissues in the diagnosis of tuberculous spondylodiscitis

Introduction Tuberculous Spondylodiscitis is the most common form of musculoskeletal tuberculosis. Molecular techniques on fresh tissues are proved to improve the diagnosis of tuberculous spondylodiscitis and to allow a rapid diagnosis to initiate the treatment and prevent neurological complications. Objectives The objective of the present study was to assess the diagnostic performances of single tube nested PCR and GeneXpert ultra in the diagnosis of tuberculous spondylodiscitis on formalin fixed paraffin embedded tissues. Methods This study included 63 tuberculous spondylodiscitis cases collected from June 2014 to January 2020 and corresponding to 27 definite tuberculous spondylodiscitis with positive microbiology, and 36 probable tuberculous spondylodiscitis, with histopathological, clinical and radiological findings consistent with tuberculous spondylodiscitis but with negative microbiology. The sensitivity, specificity, positive predictive value and negative predictive value of nested PCR and GeneXpert ultra were determined with reference to microbiology. Results Nested PCR was positive in 47 (75%) cases: 26/27 definite tuberculous spondylodiscitis and 21/36 probable tuberculous spondylodiscitis. GeneXpert ultra was positive in only 6 (10%) cases corresponding to definite tuberculous spondylodiscitis. The sensitivity, specificity, positive predictive value and negative predictive value of nested PCR on formalin fixed paraffin embedded tissues were 96%, 100%, 100%, 83% respectively. For GeneXpert ultra, these rates were 22%, 100%, 100% and 25% respectively. Conclusion Nested PCR and GeneXpert ultra on formalin fixed paraffin embedded tissues are useful tools for the diagnosis of tuberculous spondylodiscitis, especially for cases where microbiological investigations were not carried out. Both techniques have excellent specificity but single tube nested PCR is more sensitive. Key Points • Molecular techniques are routinely performed on fresh tissues • GeneXpert and nested PCR on formalin fixed paraffin embedded tissues are reliable for the diagnosis of tuberculous spondylodiscitis • Nested PCR is more sensitive than Genexpert for diagnosing tuberculous spondylodiscitis