Value of an Intrathecal Synthesis Index of Specific Antitreponema IgG for Neurosyphilis Diagnosis

The diagnosis of neurosyphilis (NS) lacks a true "gold standard" which makes the diagnosis challenging while consequences of a misdiagnosis are potentially severe. The aim of this study was to evaluate the diagnostic performance of measuring an antibody index (AI) for intrathecal synthesis of specific anti-Treponema pallidum (T. pallidum) IgG for the diagnosis of NS.

CSF parameters were analysed and specific anti-T. pallidum IgG were measured simultaneously on paired cerebrospinal fluid (CSF)-serum samples collected between 2007 and 2022 from patients suspected of NS, in Switzerland. An AI was calculated to consider blood-brain barrier integrity. Two NS definitions were used: NS1 included patients with suspicion of NS presenting neurological symptoms and/or acute neuro-sensory signs and positive TPHA/TPPA serology and CSF-TPHA/TPPA≥320, and either CSF-leucocytes >5cells/mm3 and/or CSF-protein >0,45g/l and/or a reactive CSF-VDRL/RPR test. NS2 included patients with NS suspicion presenting acute ocular and/or otologic symptoms, and positive TPHA/TPPA serology, and a favourable response to NS treatment. Controls were patients diagnosed with any other CNS pathologies and with positive TPHA/TPPA serology.

Inclusion criteria

• All patients who have serum / CSF sample pairs collected concomitantly (3 days maximum interval between blood test and lumbar puncture).
• Age > or = 18 years old.

Exclusion criteria

• All patients for whom the stored samples do not meet the needs of the diagnostic study, or whose serum and CSF collection date is more than 3 consecutive days.
• Age < 18 years old.
• No written consent form for the prospective part.