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/mm3 (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.