Searching for autoimmune encephalitis: Beware of normal CSF

Objective: To determine the prevalence of cerebrospinal fluid (CSF) markers associated with inflammation (i.e., elevated white blood cell count, protein concentration, and CSF-specific oligoclonal bands) in patients with early active autoimmune encephalitis (AE). Methods: CSF characteristics, including WBC count, protein concentration, and oligoclonal banding, were analyzed in patients diagnosed with AE at two tertiary care centers. Results: Ninety-five patients were included in the study. CSF white blood cell counts and protein levels were within normal limits for 27% (CI95%: 19-37) of patients with AE. When results of oligoclonal banding were added, 14% (CI95%: 6-16) of patients with AE had "normal" CSF. The median CSF white blood cell count was 8 cells/mm(3) (range: 0-544) and the median CSF protein concentration was 0.42 g/L (range: 0.15-3.92). Conclusions: White blood cell counts and protein levels were within normal limits in the CSF of a substantial proportion of patients with early active AE. Inclusion of CSF oligoclonal banding identified a higher proportion of patients with an inflammatory CSF profile, especially when CSF was sampled early in the disease process.