Neutrophils in cerebrospinal fluid without pleocytosis

Neutrophils in cerebrospinal fluid (CSF) samples are commonly considered a pathological feature; however, there is little information on the frequency and significance of these cells in CSF samples without pleocytosis. Therefore, the frequency and possible clinical significance of neutrophils in CSF was investigated. In a retrospective study comprising 1556 consecutive CSF samples, cytologies and patient records were reviewed. Five hundred thirty-eight CSF samples without pleocytosis were identified. Neutrophils were detected in 35.5% of these samples. The presence of neutrophils was associated with sepsis (P < 0.01), recent epileptic seizure (P < 0.0001), and blood contamination (P < 0.01). Amongst patients without CSF pleocytosis, CNS infections were not more frequent if neutrophils were present. Neutrophils are frequently observed in CSF with normal leukocyte counts. As sepsis but not CNS infection occurred more frequently in these patients, we conclude that in the absence of CSF pleocytosis, neutrophils are not indicative of CNS infections.