Neuroinvasive West Nile Virus Presenting as Subacute Progressive Quadriparesis and Intractable Pain: A Case Report

West Nile virus (WNV) is the most common mosquito-borne infection in North America; while most cases are asymptomatic, fewer than 1% develop neuroinvasive disease with significant morbidity and mortality. We report a 57-year-old man from rural Wisconsin who presented with a 10-week history of progressive asymmetric quadriparesis and severe intractable pain, preceded by fatigue, shoulder pain, and paresthesias. Neurologic examination demonstrated mild encephalopathy, bulbar involvement, and mixed upper and lower motor neuron signs. MRI showed patchy thoracic cord T2 hyperintensities and diffuse lumbar ventral root enhancement. Electrodiagnostic studies revealed diffuse active denervation and reduced compound muscle action potentials, initially raising concern for amyotrophic lateral sclerosis. Elevated WNV IgM and IgG titers in serum and cerebrospinal fluid confirmed neuroinvasive WNV infection. Despite treatment with corticosteroids and intravenous immunoglobulin, the patient deteriorated and was transitioned to hospice care. Autopsy demonstrated T-cell-mediated meningoencephalitis with widespread lymphocytic inflammation involving motor neurons, spinal cord, ventral rootlets, and peripheral nerves, consistent with diffuse axonopathy. This case underscores that neuroinvasive WNV may closely mimic motor neuron disease and emphasizes the importance of serologic testing for accurate diagnosis. Management remains supportive, and outcomes can be severe due to extensive central and peripheral nervous system involvement.