What is Tabes Dorsalis?
Tabes dorsalis is a late manifestation of neurosyphilis that affects the dorsal columns of the spinal cord and dorsal nerve roots, typically presenting 20-30 years after initial syphilis infection with sensory ataxia, loss of proprioception, neuropathic pain, and characteristic neurologic findings. 1, 2
Pathophysiology and Etiology
Tabes dorsalis represents tertiary neurosyphilis caused by Treponema pallidum infection, with degeneration specifically targeting the posterior columns of the spinal cord and dorsal roots. 1, 3 The average latency period from initial syphilis infection to symptom onset is approximately 25 years, though this can range from years to decades. 1, 3
Clinical Presentation
Cardinal Features
- Sensory ataxia with loss of proprioception that is disproportionate to other sensory modalities and motor function 4
- Neuropathic pain (often lancinating or "lightning" pains) 1
- Gait instability and chronic disequilibrium due to dorsal column dysfunction 4
- Decreased or absent deep tendon reflexes 2
- Reduced vibratory sense 2
Additional Manifestations
- Paresthesias and numbness of extremities 1
- Cranial nerve involvement (particularly VI nerve palsy, optic atrophy with vision loss) 2
- Gastrointestinal disturbances (less common) 1
- Pupillary abnormalities (Argyll Robertson pupils) 4
- Bladder dysfunction 3
Important caveat: Tabes dorsalis has become relatively rare since widespread penicillin use, with general paresis and tabes dorsalis now uncommon compared to other neurosyphilis presentations like seizures, stroke, and acute meningoencephalitis. 5
Diagnostic Approach
Serologic Testing
- Specific treponemal tests are more sensitive and specific than nontreponemal tests 5
- Critical pitfall: In more than one-third of neurosyphilis patients, nontreponemal tests (VDRL) are negative and should NOT be used to exclude the diagnosis 5
- Serum testing for Treponema pallidum antibodies is essential 2
Cerebrospinal Fluid Analysis
- CSF-VDRL (reactive test confirms neurosyphilis) 1
- Elevated Treponema pallidum activity markers in CSF 2
- Important limitation: CSF examination may show no abnormalities in neurosyphilis and is not an infallible guide to infection activity 5
Imaging
MRI of cervical and thoracic spine is the imaging modality of choice to evaluate dorsal column pathology in patients with sensory ataxia and proprioceptive loss. 4
- MRI without IV contrast is typically adequate for evaluating dorsal column involvement 4
- Contrast-enhanced imaging should be added if inflammatory, infectious, or neoplastic causes are suspected 4
- Spinal cord atrophy may be visible on MRI 4
History Taking Essentials
Obtain detailed sexual history and prior syphilis exposure (patients may not volunteer this information initially). 2 In the presented case, the patient only disclosed a history of inadequately treated syphilis 30 years prior after extensive testing was completed. 2
Treatment
Intravenous penicillin G is the only proven antibiotic treatment and is recommended for all forms of neurosyphilis. 5, 3
Rationale for High-Dose IV Therapy
- Low-dose penicillin regimens do NOT produce spirocheticidal concentrations in the brain 5
- High-dose IV penicillin therapy is necessary to ensure eradication of spirochetes 5
- Oral antibiotics are insufficient (as demonstrated by treatment failures) 2
Alternative Considerations
- Doxycycline (achieves relatively high brain concentrations) may be effective but is not first-line 5
- Ceftriaxone or azithromycin have not been adequately tested for neurosyphilis 3
Treatment Outcomes
- Laboratory results typically improve with appropriate treatment 2
- Critical limitation: Clinical improvement may not occur even with microbiologic cure, particularly when irreversible sequelae (optic atrophy, severe ataxia) have developed 2
- Early recognition and treatment are essential to prevent permanent neurologic damage 2
Prognosis and Natural History
Tabes dorsalis can cause progressive disability if untreated, but the natural evolution remains incompletely understood. 6 Once advanced neurologic damage occurs (severe gait ataxia, optic atrophy, complete loss of proprioception), treatment may halt progression but not reverse deficits. 2
HIV coinfection consideration: All patients diagnosed with syphilis should be offered HIV testing, as syphilis facilitates HIV transmission and vice versa. 3