An evaluation of oligoclonal banding and CSF IgG index in the diagnosis of neurosyphilis.

It can be difficult to determine which patients would benefit from therapy to control central nervous system infection with Treponema pallidum. The authors have followed patients prospectively to evaluate two new diagnostic tests available. They performed lumbar punctures on 107 consecutive patients with syphilis of unknown duration, untreated (n = 19) or with serology that did not decrease sufficiently during follow-up (n = 88). The mean age was 47 years, with 91 males and 16 females. Twelve had neurologic symptoms. In order to establish a gold standard, the authors required the cerebrospinal fluid Venereal Disease Research Laboratory (CSF VDRL) test to be reactive (n = 25). They then examined oligoclonal banding and CSF IgG index as diagnostic tests by comparing them to the gold standard. Oligoclonal banding, abnormal in 20, had a sensitivity of 52% and a specificity of 91%. The CSF IgG index, abnormal in 56, had a sensitivity of 92% and a specificity of 60%. The posttest likelihoods of a positive test result were low, and hence neither test ruled in the diagnosis. With a post-test likelihood (PTL) negative of 4%, a negative CSF IgG index assisted in ruling out the diagnosis. Oligoclonal banding was not a satisfactory test for neurosyphilis. The CSF IgG index appears to help only in ruling out infection. Further effort is needed in developing diagnostic tests to assist the clinician in the diagnosis of neurosyphilis.