To explore immunological diagnostic characteristics in serum and cerebrospinal fluid (CSF) of neurosyphilis patients.

Thirty-five patients with neurosyphilis admitted to Xuanwu Hospital of Capital Medical University during June 2013 to July 2016 were selected for retrospective analysis, including 32 patients with serum and CSF immunological test results. Fisher exact test was used to compare the differences of IgA and IgM between serum group and cerebrospinal fluid group meanwhile, the difference of IgG between serum and cerebrospinal fluid group was compared using Chi-square test. The positive detection rate of oligoclonal bands (OB) and the 24-hour synthesis rate of immunoglobulin in cerebrospinal fluid were also analyzed.

Serum and CSF Immunoglobulin levels were in 32 patients with neurosyphilis. In serum group, IgG level elevated in 53.13%(17/32) patients, IgA level elevated in 6.25% (2/32) patients, and IgM level elevated in 0% (0/32) patient. Nevertheless, CSF-IgG increased in 84.38% (27/32) patients, CSF-IgA increased in 100.00% (32/32) patients and CSF-IgM increased in 90.63% (29/32) patients. There were statistically significant differences in the elevation rate of IgA and IgM between the serum and cerebrospinal fluid group (χ²=56.47, 53.03, P<0.01). There was no statistically significant difference in the elevation rate of IgG between the two groups(χ²=7.27, P>0.05). The positive rate of oligoclonal band in cerebrospinal fluid was as high as 100.00%, the 24-hour synthesis rate of immunoglobulin in cerebrospinal fluid increased in 96.00% (24/25) patients.

Neurosyphilis, with various clinical manifastations, is a treatable and easily misdiagnosed disease. Humoral immunity may play an important role in its development. Serum and CSF IgG increase, CSF IgA and IgM elevation and serum IgA and IgM are normal, CSF OB positive, CSF-24 h IgG synthetic ratio elevation are meaningful immunological characteristics for neurosyphilis diagnosis.