Abstracts

Rationale: The diagnosis of autoimmune encephalitis (AE) has increased since the detection of new neuronal autoantibodies. Recently proposed diagnostic criteria for AE (Graus et al., Lancet 2016) do not require positive antibody status to consider AE as having a definite autoimmune origin. However, detection of autoantibodies remains important: their presence clarifies the immunological subgroup of AE, prognosis, and, detection establishes the diagnosis in patients with uncertain diagnosis. However, not all patients with autoimmune encephalitis have antibodies, and the absence of antibodies does not rule out an autoimmune mechanism. Literature reviews and expert opinion report that paraclinical markers such as evidence of CNS inflammation and abnormal serological markers of systemic autoimmunity may aid in the diagnosis of an underlying autoimmune process (Linnoila et al, Semin Neurol 2016), but there has been limited to no data reported on the sensitivities of paraclinical markers in autoimmune encephalitis. The purpose of this study is to investigate the sensitivity of paraclinical markers, specifically CSF and serum markers of systemic autoimmunity, in the diagnosis of AE. Methods: A retrospective case series was created with an institutional database analysis was performed to identify patients that had abnormal autoimmune panels or autoantibodies associated with autoimmune encephalitis (i.e. VGKC, NMDA-R, etc) that were ordered between the years 2010-2017. In addition, we enrolled patients under the care of Northwestern physicians with a known clinical diagnosis of definite AE or probable AE with a clinical response to immunosuppression. Data was stored using NU’s REDCap database and consent was obtained by the patient or a legal authorized representative. Results: Sixteen patients were included in this retrospective case series. The mean age was 37.4 years. Positive autoantibody was found in the serum 12/15 cases and in the CSF of 3/14 cases.  Initial CSF evaluation was normal in 50% of our patients. CSF oligoclonal bands and IgG Index were normal in all patients that received testing. Thyroid peroxidase (TPO) and anti-thyroglobulin (TG) antibody was abnormal in 5/12 (42%) and 4/12 (33%) of patients tested, respectively. ANA with titers > 1:80 were seen in 4/14 (29%) patients. Of note, in three of our autoantibody negative patients, one patient was found to have an ANA of 1:1280 including positive Anti-SSA (RO) and Anti-SSB (LA) antibodies while a second patient had a greater than 10-fold increase of both TPO and Anti-TG antibodies. Conclusions: Ancillary testing of paraclinical markers including systemic markers of autoimmunity and CSF analysis, may be suggestive of a CNS autoimmune process. There is limited to no published data on the sensitivity and specificity of serum paraclinical markers in AE. In our cohort, we did not identify oligoclonal bands or elevated IgG index which is not consistent with published literature, but the variance may be due to small sample size which is a limitation. We plan to continue to enroll patients and potentially utilize findings of paraclinical markers to contribute to formulation of diagnostic guidelines. Funding: None