Electrodiagnostic features of acute paralytic poliomyelitis associated with West Nile virus infection.

West Nile virus (WNV) infection is a potentially fatal disease, with meningoencephalitis being its most common neurological manifestation. Guillain-Barré syndrome (GBS) has also been described, but acute paralytic poliomyelitis has only recently been recognized. We report the clinical and electrodiagnostic findings of five patients with WNV infection, who presented with acute paralytic poliomyelitis. Three patients manifested focal asymmetrical weakness, and two had rapid ascending quadriplegia mimicking GBS. Electrodiagnostic studies during the acute illness showed normal sensory nerve action potentials, compound motor action potentials of normal or reduced amplitude, and no slowing of nerve conduction velocities. Depending on the timing of the examination, fibrillation potentials were widespread, including in those with focal weakness. Cervical magnetic resonance imaging in one patient showed abnormal T2-weighted signals in the spinal cord gray matter. On follow-up, signs of clinical improvement were seen in one patient, whereas two remained quadriplegic and ventilator-dependent 5 months after the onset. This report highlights the value of the electrodiagnostic studies in the diagnosis and prognosis of focal or generalized weakness due to acute paralytic poliomyelitis associated with WNV infection.