Antibodies to antigen A60 in cerebrospinal fluid from patients with tuberculous meningitis

Cerebrospinal fluid (CSF) anti-mycobacterial antigen 60 (A60) IgM, IgG and IgA in patients affected by meningitis of different etiologies were assayed as a rapid diagnostic test in cases of tuberculous meningitis. A commercial EIA was used to test 127 CSF samples classified as follows: tuberculous meningitis (n = 27 CSF samples from 16 patients, 6 of them with AIDS), pyogenic meningitis (n = 13), non-tuberculous aseptic meningitis (n = 43) and 44 normal CSF samples (16 of them from HIV-positive patients, 8 of whom had extraneurological tuberculosis). Anti-A60 IgM was positive only in two cases (1 tuberculous meningitis and 1 self-resolving aseptic meningitis). Positive CSF anti-A60 IgG and IgA were observed in eight and nine out of 16 patients with tuberculous meningitis, but only in four and five out of 13 samples studied prior to or in the first ten days of treatment, respectively. Most of the patients with false-positive IgG and IgA (16%) had pyogenic meningitis, but without intrathecal synthesis of antibodies. In patients with aseptic meningitis, the finding of CSF anti-A60 IgG plus IgA, initially or during follow-up, can be used as a diagnostic criterion for tuberculous meningitis, with a specificity of 100%, a positive predictive value of 1, and a negative predictive value of 0.81. However, its sensitivity is only 50% in immunocompetent patients and 16% in patients with AIDS.