Detection of mycobacterial antigen in cerebrospinal fluid: diagnostic and prognostic significance

Inhibition enzyme-linked immunosorbent assay (ELISA) was standardised to quantitate circulating mycobacterial antigens in cerebrospinal fluid (CSF) specimens. Of the 40 patients with clinical diagnosis of tuberculous meningitis, the assay was found to be positive in 26 patients. In a control group of 42 patients with non-tuberculous neurological diseases the assay was negative. The assay showed a sensitivity of 65 and 100% specificity for tuberculous meningitis. In 8 patients with tuberculous meningitis receiving chemotherapy, multiple CSF examinations were subjected to this assay. The antigen concentration showed a gradual decrease between 3 and 4 weeks after the commencement of antituberculosis chemotherapy. There was a positive correlation between clinical recovery and antigen concentration. Detection of mycobacterial antigen in CSF specimen by inhibition ELISA has not only diagnostic utility but also could be applied to monitor antituberculosis chemotherapy in patients with tuberculous meningitis. The assay is reproducible and feasible for routine immunology laboratory. It also could be considered as a diagnostic aid when repeated bacteriological cultures are negative in CSF specimens of patients with tuberculous meningitis.