Does West Nile Virus Attack Anterior Horn Cells Like Poliovirus?
Yes, West Nile virus (WNV) directly attacks anterior horn cells in the spinal cord, producing a poliomyelitis-like syndrome that is clinically and pathologically similar to poliovirus infection. 1, 2
Mechanism of Paralysis
Anterior Horn Cell Involvement
- WNV causes acute flaccid paralysis through direct damage to anterior horn cells in the spinal cord, creating a clinical picture indistinguishable from classic poliomyelitis 1, 2
- Neurophysiological, radiological, and pathological studies confirm that WNV damages motor neurons in the anterior horn, not peripheral nerves 3
- The disease mechanism involves viral replication within motor neurons, similar to poliovirus, which "replicates in motor neurons of the anterior horn and brain stem resulting in cell destruction" 4
Clinical Presentation Parallels
- Patients develop asymmetric flaccid weakness with areflexia but no sensory abnormalities, matching the classic polio presentation 1, 2
- The weakness progresses rapidly over 2-4 days, similar to poliovirus paralysis 1
- Deep tendon reflexes are absent or diminished, consistent with lower motor neuron involvement 1, 2
Diagnostic Features Distinguishing WNV from Peripheral Neuropathy
Electrodiagnostic Findings
- Clinical and electrodiagnostic data demonstrate involvement of spinal anterior horn cells rather than peripheral demyelination (Guillain-Barré syndrome) 1, 2
- The pathologic process involves anterior horn cells and motor axons, not the myelin sheath 2
Neuroimaging Evidence
- MRI shows prominent hyperintensities in the spinal cord gray matter (anterior horn), confirming poliomyelitis-like pathology 5
- Brainstem involvement may also be visible, similar to bulbar polio 5
Clinical Recognition in Practice
Key Distinguishing Features from GBS
- Absence of sensory abnormalities is critical—WNV-associated AFP spares sensory function entirely 1
- Asymmetric pattern of weakness (versus the typically symmetric presentation of GBS) 1, 2
- Fasciculations may be present at onset, indicating anterior horn cell involvement 5
Associated Neurological Manifestations
- Movement disorders including tremors and parkinsonian features can occur with WNV due to thalamic and basal ganglia involvement 4
- Encephalitis with acute flaccid paralysis is characteristic of flaviviruses including WNV, similar to polio and other enteroviruses 4
- Nigral degeneration with neurofibrillary tangle formation has been documented pathologically 6
Clinical Implications
Diagnostic Approach
- In areas with WNV transmission, consider WNV infection in any patient presenting with acute flaccid paralysis 1, 2
- Test serum and CSF for WNV-specific IgM antibodies 4
- Pregnant women with acute flaccid paralysis in endemic areas require WNV testing 4
Avoiding Inappropriate Treatment
- Recognition that weakness originates from spinal anterior horn cells (not peripheral demyelination) prevents inappropriate treatment with IVIG or plasmapheresis 1
- Unlike GBS, this is a direct viral cytopathic process, not an immune-mediated peripheral neuropathy 3