Delayed-onset and recurrent limb weakness associated with West Nile virus infection.

Human neurologic illness following infection with West Nile virus (WNV) may include meningitis, encephalitis, and acute flaccid paralysis (AFP). Most WNV-associated AFP is due to involvement of the spinal motor neurons producing an anterior (polio)myelitis. WNV poliomyelitis is typically characterized by acute and rapidly progressing limb weakness occurring early in the course of illness, which is followed by death or clinical plateauing with subsequent improvement to varying degrees. We describe four cases of WNV poliomyelitis in which the limb weakness was characterized by an atypical temporal pattern, including one case with onset several weeks after illness onset, and three cases developing relapsing or recurrent limb weakness following a period of clinical plateauing or improvement. Delayed onset or recurrent features may be due to persistence of viral infection or delayed neuroinvasion with delayed injury by excitotoxic or other mechanisms, by immune-mediated mechanisms, or a combination thereof. Further clinical and pathogenesis studies are needed to better understand the mechanisms for these phenomena. Clinicians should be aware of these clinical patterns in patients with WNV poliomyelitis.