Infectious Disease · Treponema pallidum infection
The facts most likely to be tested
Tabes dorsalis presents as demyelination of the dorsal columns and dorsal nerve roots, leading to sensory ataxia, lancinating pains, and loss of proprioception.
Argyll Robertson pupils are pathognomonic for neurosyphilis, characterized by pupils that accommodate but do not react to light.
General paresis manifests as progressive dementia, personality changes, and psychiatric disturbances due to chronic meningoencephalitis.
Lumbar puncture with CSF-VDRL is the diagnostic test of choice for neurosyphilis, though it has low sensitivity and high specificity.
A reactive serum treponemal test (e.g., FTA-ABS) is required to screen for syphilis before confirming neurosyphilis with CSF analysis.
Intravenous aqueous crystalline penicillin G for 10–14 days is the first-line treatment for all stages of neurosyphilis.
Jarisch-Herxheimer reaction is an acute febrile response occurring within 24 hours of initiating antibiotic therapy due to the rapid lysis of spirochetes.
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A 58-year-old male presents to the clinic with a 6-month history of progressive gait instability and shooting pains in his legs. Physical examination reveals bilateral pupils that constrict with accommodation but fail to constrict to light. He has absent deep tendon reflexes in the lower extremities and impaired vibration and position sense in the feet. A serum RPR is reactive, and a confirmatory FTA-ABS is positive.
What is the most appropriate next step in the management of this patient?
Lumbar puncture for CSF-VDRL analysis
The patient's clinical presentation of tabes dorsalis and Argyll Robertson pupils is highly suggestive of neurosyphilis; therefore, a lumbar puncture is required to confirm the diagnosis and guide treatment.
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Etiology / Epidemiology
Caused by Treponema pallidum invasion of the CNS; occurs in patients with untreated syphilis and high-risk sexual behavior.
Clinical Manifestations
Presents as tabes dorsalis, Argyll Robertson pupils, or general paresis. Meningovascular or parenchymatous involvement.
Diagnosis
Requires CSF-VDRL (highly specific) and CSF pleocytosis (>5 WBC/µL).
Treatment
Aqueous crystalline penicillin G IV is the gold standard. Penicillin allergy requires desensitization.
Prognosis
Irreversible damage if untreated; CSF cell count normalization is the primary marker of treatment success.
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Epidemiology & Etiology
Neurosyphilis can occur at any stage of infection, though it is most common in the tertiary phase. Patients with HIV coinfection are at significantly higher risk for rapid progression. It results from hematogenous spread of the spirochete to the CNS.
Pertinent Anatomy
Infection targets the meninges (meningovascular syphilis) and the dorsal columns of the spinal cord. Involvement of the midbrain tectum leads to the classic pupillary findings.
Pathophysiology
The spirochete induces an inflammatory response causing obliterative endarteritis of small vessels. This leads to ischemia and infarction of neural tissue. Chronic inflammation results in the demyelination of the posterior columns.
Clinical Manifestations
Argyll Robertson pupils (accommodate but do not react to light) are pathognomonic. Tabes dorsalis presents with sensory ataxia and lancinating pains. General paresis manifests as progressive dementia and personality changes. Meningovascular forms present with acute stroke-like symptoms in young patients.
Diagnosis
Diagnosis is confirmed by a reactive CSF-VDRL test. A reactive serum FTA-ABS is required for screening. CSF pleocytosis (>5 WBC/µL) or elevated CSF protein (>45 mg/dL) supports the diagnosis.
Treatment
The treatment of choice is Aqueous crystalline penicillin G (18–24 million units/day IV). Penicillin allergy is a major barrier; patients must undergo desensitization rather than using alternative antibiotics. Ceftriaxone is an inferior alternative for those who cannot be desensitized.
Prognosis
Treatment halts progression but rarely reverses established neurological deficits. Patients require repeat lumbar puncture every 6 months until the CSF cell count returns to normal. Failure to normalize suggests treatment failure or HIV-related progression.
Differential Diagnosis
Multiple Sclerosis: optic neuritis and relapsing-remitting course
Lyme Disease: history of tick bite and erythema migrans
HIV-associated neurocognitive disorder: absence of reactive CSF-VDRL
B12 Deficiency: subacute combined degeneration with macrocytic anemia
Diabetes Mellitus: peripheral neuropathy without pupillary changes