Microbiological and immunological diagnosis of tuberculous spondylodiscitis

Tuberculous spondylodiscitis is one the many manifestations of active tuberculosis (TB) and can result following primary infection or, more frequently, from reactivation of active TB in subjects with latent TB. Definitive diagnosis of tuberculous spondylodiscitis requires the identification of Mycobacterium tuberculosis in the biological sample following microbiological analysis.

To summarize the recent advancement in the diagnosis of TB, focusing on classical and molecular microbiological procedures, providing an overview on the recent advancements in the understanding of TB pathogenesis and their implications for the immunological diagnosis

Isolation in culture of the bacilli and detection using molecular tools are the gold standards, though sensitivity of these assays is significantly lower compared to what observed for pulmonary TB, making diagnosis of spinal TB challenging.

The use of the interferon-gamma release assays (IGRAs) for the immunological diagnosis of TB infection could be of help and shall precede the invasive techniques, such as biopsy or surgery, required to obtain the biological sample. IGRAs measure the presence of effector T cells in the blood that can readily respond to an antigenic stimuli by secreting cytokines, and that are an indication of the presence of the bacilli in vivo. IGRAs are more sensitive and specific than the intradermic reaction of Mantoux, though both these immunological tests cannot distinguish between latent TB infection and active TB.

A modern diagnosis of TB spondylodiscitis should rely on the use of microbiological and immunological assays and the latter could potentially be of great help in monitoring therapy effectiveness.