Definition and epidemiology
Neurosyphilis refers to infection of the central nervous system (CNS) by Treponema pallidum, the spirochete that causes syphilis. It can occur at any stage of syphilis, from early invasion of the CSF within weeks of infection to late destructive disease decades later.
Syphilis remains a global public health problem, with rising incidence in many high-income countries over the past two decades, particularly among men who have sex with men and people living with HIV. HIV coinfection increases the risk of neurologic involvement and accelerates the timeline to symptomatic neurosyphilis.
- Early neurosyphilis (asymptomatic or symptomatic meningitis, meningovascular disease): typically within the first 1-2 years of infection
- Late neurosyphilis (general paresis, tabes dorsalis): classically 10-30 years after primary infection, now less common due to earlier antibiotic treatment of syphilis
- Before the antibiotic era, neurosyphilis was a leading cause of psychiatric hospitalization and death; it is now uncommon but still seen, especially in under-screened and HIV-positive populations
- Argyll Robertson pupil accommodates but does not react to light - classic for tabes dorsalis.
- CSF-VDRL is specific but not very sensitive; a negative result does not rule out neurosyphilis.
- Benzathine penicillin IM does not adequately treat neurosyphilis due to poor CSF penetration.
- Tabes dorsalis causes sensory ataxia, loss of proprioception/vibration, and absent reflexes from dorsal column/root damage.
- Meningovascular syphilis causes stroke-like deficits in younger patients without typical vascular risk factors.
- All patients diagnosed with neurosyphilis should be tested for HIV.
- Charcot (neuropathic) joints result from loss of proprioceptive protection in tabes dorsalis.
- Treatment is IV aqueous penicillin G for 10-14 days; CSF parameters are monitored for response.
Etiology and risk factors
The causative organism is Treponema pallidum subspecies pallidum, a spirochete acquired through sexual contact (or vertically, causing congenital syphilis). CNS invasion can happen early in infection, but clinical neurosyphilis develops only in a minority of untreated patients.
Risk factors
- Untreated or inadequately treated syphilis
- HIV coinfection (strongest modifiable risk factor; associated with higher rates of CSF abnormalities and faster progression)
- Men who have sex with men, in current epidemiologic data from many countries
- Lack of access to screening and early treatment
- History of multiple sexually transmitted infections
Neurosyphilis is not a distinct serotype or strain-specific disease; it reflects failure to clear spirochetes from the CNS, which can happen even after treatment of early syphilis if that treatment did not adequately penetrate the CSF (notably with benzathine penicillin, which has poor CNS penetration).
Pathophysiology
T. pallidum crosses the blood-brain barrier early in infection in a substantial proportion of patients, but the host immune response usually clears it. When clearance fails, chronic CNS infection produces a spectrum of disease depending on the predominant site of damage.
Patterns of disease
- Asymptomatic neurosyphilis: CSF abnormalities (pleocytosis, elevated protein, reactive CSF-VDRL) without clinical symptoms
- Syphilitic meningitis: early, resembles other subacute aseptic meningitides, may involve cranial nerves
- Meningovascular syphilis: obliterative endarteritis of small and medium vessels causes ischemic stroke, typically in younger patients without usual vascular risk factors
- General paresis (paretic neurosyphilis): chronic meningoencephalitis causing cortical atrophy, especially frontal and temporal lobes, producing progressive dementia and psychiatric disturbance
- Tabes dorsalis: inflammatory destruction of the dorsal columns and dorsal (posterior) nerve roots, causing sensory ataxia and loss of proprioception/vibration sense
- Gummatous neurosyphilis: rare, mass-like granulomatous lesion
The Argyll Robertson pupil results from a lesion disrupting the light-reflex pathway near the pretectal area while sparing the near-reflex pathway, classically seen in tabes dorsalis.
Clinical features
Presentation depends heavily on which pattern predominates and overlaps occur frequently.
Early neurosyphilis
- Headache, neck stiffness, photophobia (meningitis)
- Cranial neuropathies (especially CN VII and VIII)
- Stroke-like focal deficits in a younger patient (meningovascular form)
General paresis ("paresis" = weakness, but clinically dominated by cognitive decline)
- Progressive dementia, personality change, impaired judgment
- Mood disturbance, psychosis, delusions of grandeur (classically described, not universal)
- Tremor, dysarthria, seizures in advanced disease
Tabes dorsalis
- Lightning (lancinating) pains in the legs
- Sensory ataxia, wide-based gait, worse in the dark (positive Romberg sign)
- Loss of vibration and proprioception, absent deep tendon reflexes
- Urinary incontinence or retention
- Charcot joints (neuropathic joint destruction) from loss of proprioceptive protection
Pupillary findings
- Argyll Robertson pupil: small, irregular pupil that constricts with accommodation/near effort but not with light ("accommodates but does not react")
Diagnosis
Diagnosis requires a combination of serologic testing, clinical features, and CSF analysis; no single test is perfectly sensitive or specific.
Serologic tests
- Nontreponemal tests (RPR, VDRL): used for screening and monitoring treatment response
- Treponemal tests (FTA-ABS, TPPA, EIA): confirm exposure, remain positive for life
CSF analysis (lumbar puncture required when neurosyphilis is suspected)
- CSF-VDRL: highly specific but insensitive; a reactive CSF-VDRL confirms neurosyphilis
- CSF white cell count: elevated (lymphocytic pleocytosis) supports active disease and is used to monitor treatment response
- CSF protein: typically elevated
- FTA-ABS on CSF: sensitive but less specific (can be falsely positive from blood contamination); a negative CSF FTA-ABS argues against neurosyphilis
| Test | Sensitivity | Specificity |
|---|---|---|
| CSF-VDRL | Low-moderate | High |
| CSF FTA-ABS | High | Lower |
| Serum treponemal test | High | High (for syphilis exposure) |
Additional workup
- HIV testing in all patients with syphilis
- MRI brain in patients with focal deficits, dementia, or stroke-like presentation (may show cortical atrophy, infarcts, or nonspecific white matter changes)
- Ophthalmologic exam if ocular syphilis is suspected (a related entity requiring the same CSF-based treatment approach)
Differential diagnosis
- HIV-associated neurocognitive disorder / HIV encephalopathy: dementia in an HIV-positive patient without reactive syphilis serology
- Other causes of subacute dementia: Alzheimer disease, frontotemporal dementia, normal pressure hydrocephalus, Creutzfeldt-Jakob disease
- Multiple sclerosis: can mimic tabes dorsalis with sensory symptoms and gait disturbance, but demographics, MRI, and CSF profile differ
- Vitamin B12 deficiency (subacute combined degeneration): also affects dorsal columns, but typically also involves corticospinal tracts and has distinct hematologic findings
- Diabetic peripheral neuropathy / autonomic neuropathy: can cause sensory ataxia and Charcot joints
- Other causes of aseptic meningitis: viral, tuberculous, fungal meningitis
- Stroke from atherosclerotic disease: meningovascular syphilis mimics stroke, but occurs in younger patients with syphilis risk factors
Management
Neurosyphilis at any stage, and ocular/otic syphilis, requires treatment regimens that achieve adequate treponemicidal levels in the CSF; standard intramuscular benzathine penicillin does not penetrate the CSF reliably and is inadequate.
First-line (per CDC and WHO/European guidelines)
- Aqueous crystalline penicillin G, given intravenously, for 10-14 days
- Alternative: procaine penicillin intramuscularly combined with oral probenecid, for 10-14 days, in settings where IV therapy is impractical
Penicillin allergy
- Confirmed penicillin allergy: desensitization and penicillin treatment is preferred, especially in pregnant patients or those with HIV
- Alternatives with less robust evidence include ceftriaxone (used in some protocols given CSF penetration) or doxycycline in select non-pregnant patients, under specialist guidance
Monitoring
- Repeat CSF examination (cell count, protein, CSF-VDRL) at intervals (commonly every 6 months) until CSF white cell count normalizes
- Clinical improvement is expected, but preexisting deficits (e.g., tabetic sensory loss) may be irreversible
- All patients should be tested for HIV, and partners should be notified and offered testing/treatment per public health protocols
- A Jarisch-Herxheimer reaction (fever, worsening symptoms) can occur after the first dose due to spirochete lysis and is managed supportively
Complications and prognosis
Prognosis depends heavily on the stage and extent of CNS damage at the time treatment begins.
- Early neurosyphilis (meningitis, meningovascular disease) generally responds well to treatment with good recovery, though stroke-related deficits may persist
- General paresis: treatment halts progression, but established cognitive deficits often do not fully reverse
- Tabes dorsalis: sensory ataxia, lancinating pains, and Charcot joints are often irreversible once established, even with adequate antimicrobial therapy
- Relapse or treatment failure can occur, particularly in untreated HIV coinfection, warranting repeat CSF evaluation
- Without treatment, neurosyphilis can progress to severe disability, dementia, paralysis, and death
Argyll Robertson pupil = "Accommodates but does not React" - think of it as a "prostitute's pupil": accommodates (to near) but doesn't react (to light).
Practice questions
1. A 52-year-old man presents with a 6-month history of progressive memory loss, irritability, and grandiose statements about his wealth. His wife reports a tremor and slurred speech developing recently. He has a history of a painless genital ulcer 20 years ago that resolved untreated. Neurologic exam shows cognitive impairment and dysarthria. Which of the following is the most likely diagnosis?
2. A 60-year-old man presents with a wide-based, unsteady gait that worsens markedly when he closes his eyes while standing. He also reports brief, severe shooting pains in his legs. Exam reveals absent ankle and knee reflexes, impaired vibration and position sense in the lower extremities, and small irregular pupils that constrict with near focus but not with light. Which of the following is the most likely underlying mechanism?
3. A 34-year-old man with HIV infection (not on antiretroviral therapy) presents with acute right hemiparesis and aphasia. CT angiogram shows no large vessel occlusion. Serum RPR is reactive at high titer, confirmed with a treponemal test. Lumbar puncture shows CSF pleocytosis and a reactive CSF-VDRL. Which of the following is the most appropriate treatment?
Frequently asked questions
What causes neurosyphilis?
Neurosyphilis is caused by invasion of the central nervous system by Treponema pallidum, the spirochete bacterium responsible for syphilis. It occurs when syphilis is left untreated or inadequately treated, allowing the organism to persist in the brain, spinal cord, or meninges, often years after the initial infection. HIV coinfection significantly increases the risk.
What are the first symptoms of neurosyphilis?
Early symptoms often include headache, neck stiffness, and cranial nerve problems from syphilitic meningitis, or sudden stroke-like weakness from meningovascular involvement in a younger person. Later presentations include personality change and memory problems (general paresis) or lightning pains and unsteady gait (tabes dorsalis). Symptoms vary widely by stage and pattern.
How is neurosyphilis diagnosed?
Diagnosis combines a positive syphilis serology with a lumbar puncture showing CSF abnormalities, especially a reactive CSF-VDRL, elevated white cell count, and elevated protein. Clinical findings like the Argyll Robertson pupil or sensory ataxia support the diagnosis. Because no single test is perfectly accurate, results are interpreted together with the clinical picture.
Is neurosyphilis curable?
The infection itself is curable with intravenous penicillin G for 10-14 days, which stops disease progression and often improves symptoms like meningitis or stroke-related deficits. However, damage already present in advanced disease, such as the sensory loss of tabes dorsalis or established dementia in general paresis, may be permanent even after successful treatment. Early diagnosis improves the chance of full recovery.
Tabes dorsalis vs general paresis - what is the difference?
Tabes dorsalis primarily damages the dorsal columns and dorsal nerve roots of the spinal cord, causing sensory ataxia, lancinating pains, and loss of proprioception/vibration sense. General paresis is a chronic meningoencephalitis affecting the brain cortex, causing progressive dementia, personality change, and psychiatric symptoms. Both are late forms of neurosyphilis and can coexist in the same patient.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: A52.1
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.