Clinical and neuroradiologic features of 39 consecutive cases of West Nile Virus meningoencephalitis

Background: West Nile Virus (WNV) is a flavivirus WNV that has spread westwards across North America in recent years. It can cause a febrile illness and infection of the central nervous system, which is associated with poor outcome. Methods: We retrospectively studied the clinical and neuroradiologic features of 39 consecutive patients admitted during summer of 2002 that had IgM in the cerebrospinal fluid positive for WNV. Results: Fever, headache and altered mentation were predominant clinical features. Clinically significant involvement of lower motor neurons was seen in few cases. Magnetic resonance imaging (MRI) of the brain did not show changes attributable to meningitis or encephalitis except for one case of subcortical signal abnormalities. Unfavorable prognostic factors are old age, decreased level of alertness and elevated serum creatinine. Conclusions: Encephalopathic presentations, with or without additional neurological focality, dominated this series. Fever and meningitic signs are often absent. Involvement of lower motor neurons was uncommon. Given the paucity of positive findings, the value of MRI to support the diagnosis of WNV-meningoencephalitis is limited.