Syphilis and neurosyphilis in people living with HIV: analysis of cerebrospinal fluid findings

Background Syphilis and neurosyphilis remain significant comorbidities among people living with human immunodeficiency virus (HIV). Data on cerebrospinal fluid (CSF) findings in co-infected individuals are limited. This study aimed to determine which CSF parameters and HIV-related immunologic and virologic markers are associated with neurosyphilis in people living with HIV (PLWH), and to assess the impact of antiretroviral therapy (ART) on these relationships. Methods We conducted a retrospective analysis of 211 people living with HIV undergoing syphilis serology and CSF testing at a tertiary care center between 2011 and 2017. Patients were stratified by syphilis stage and ART status. CSF parameters, CD4 + /CD8 + cell counts, HIV viral load, and syphilis diagnostic parameters were analyzed. Results Neurosyphilis was diagnosed in 10% (n = 21) of the study population. Treponema pallidum particle agglutination (TPPA) titers ≥ 1024 in CSF were significantly associated with neurosyphilis (p = 0.001). No significant association was observed between neurosyphilis and CD4 + count < 200/μL (p = 0.67) or detectable CSF HIV viral load (p = 0.83). ART success was associated with lower CSF viral loads (p < 0.001), higher CD4 + counts (p < 0.001), and CD4 + /CD8 + ratios (p = 0.001). CSF immunoglobulin levels (IgA, IgG, IgM) differed significantly between patients on ART and those not receiving ART, whereas leukocyte counts and protein levels showed no differences. Conclusions High CSF TPPA titers, particularly ≥ 1024, are strong indicators of neurosyphilis among PLWH. CD4 + count and CSF HIV RNA were not predictive of neurosyphilis, underscoring the diagnostic challenge posed by HIV co-infection. ART success influences CSF immunological parameters but not neurosyphilis risk directly.