Cerebrospinal fluid cytology in seasonal epidemic West Nile virus meningo-encephalitis

The incidence of West Nile Virus (WNV) infection has progressively increased in North America since the first epidemic in 1999. Formal scholarly documentation of cerebrospinal fluid (CSF) cytology changes in patients with WNV infection is limited. We report our experience with CSF cytospins from a population of consecutive patients with documented CSF WNV-specific IgM. Thirty-two patients (12 male, 20 .female) with a median age of 52 yr (range, 19-88) diagnosed with WNV meningo-encephalitis were studied. Symptoms were present for a mean of 5 days (range, 1-14) prior to lumbar puncture. CSF proteins were elevated in 94% of patients (30/32) with a mean value of 79 mg/dl (range, 36-185). CSF glucose was normal to elevated in all cases. All cytomorphologically adequate samples demonstrated a pleocytosis with a mean of 156 cells/mm(3) (range, 13-683). Nearly, all (26/28) patients showed increased CSF neutrophils- mean 43% (range, 1-83). Mean lymphocyte and monocyte fractions were 44% (range, 8-85) and 14% (range, 2-27), respectively. Three cases showed 1-4% plasma cells. Mean total leukocyte counts (TLC) (197 cells/mm(3)) and mean neutrophil fractions (50%) were greater in patients sampled within the first 3 days of symptoms than in those sampled beyond day 3 (mean TLC, 126 cells/mm(3) mean neutrophil fraction, 37%). Relative lymphocyte proportions increased from a mean of 39 to 48% after 3 days of illness. WNV should be considered as a potential etiology of infections CSF pleocytosis in the North American late summer and early fall seasons.