Plasma cell pleocytosis in cerebrospinal fluid in patients with West Nile virus encephalitis.

We describe 4 patients with West Nile virus encephalitis who all displayed previously unreported plasma cell pleocytosis of the cerebrospinal fluid (CSF). Three patients recovered but had varying degrees of mild neurologic disability on discharge from the hospital, and 1 patient died. The finding of significant numbers of plasma cells in CSF may serve as a useful early diagnostic clue for West Nile virus encephalitis.