Introduction:
Syphilis, caused by the spirochete Treponema pallidum, despite its declining incidence, still represents a significant concern for public health. The report presents the case of a 42-year-old man with concurrent tertiary syphilis, manifesting as neurosyphilis, and human immunodeficiency virus (HIV) infection. The patient was admitted to the department due to qualitative disturbances of consciousness; alcohol-related encephalopathy was initially suspected in the preliminary diagnostic process. Routine laboratory and toxicology tests showed no significant abnormalities and did not indicate the presence of infectious factors. Brain imaging findings were non-specific, and the initial cerebrospinal fluid examination also did not allow for a definitive diagnosis

Results:
Extended serological testing revealed HIV infection, which facilitated the diagnosis of late-stage syphilis. The patient was treated with intravenous crystalline penicillin and antiretroviral therapy was initiated. This case demonstrates that the diagnosis of neurosyphilis in HIV-infected individuals remains a significant diagnostic challenge, as standard serological tests, including VDRL, may yield false-negative or inconsistent results.

Conclusions:
The case highlights the need for comprehensive diagnostic evaluation and a high degree of clinical vigilance, particularly in patients with a complex medical history, neuropsychiatric symptoms, and co-existing suspicion of immunodeficiency.