Antibody negative autoimmune encephalitis- Does it differ from definite one?

Context: Autoimmune encephalitis (AE) is an emerging cause of non-infective encephalitis, presentations of which vary widely. Traditionally the diagnosis of AE is based on detection of antibodies in a patient with clinical picture suggestive of AE. Aim: To evaluate the clinical characteristics and response to immunotherapy in patients with antibody negative autoimmune encephalitis and to compare them with definite cases. Settings and Design: A prospective follow-up study was done in patients presenting with presumptive symptoms of AE from January 2017 to January 2019. The study was done in a tertiary care institute of Northern India. Patients and Methods: Demographic and clinical parameters were noted and relevant investigations for management were done according to well-defined protocol. The patients were treated with immunomodulatory therapy in the form of steroids and/or intravenous immunoglobulins (IVIg). They were followed up for treatment response and relapse at 2 monthly intervals. Statistical Analysis Used: The data was expressed as either proportions or mean/median. Chi-square test/Independent T test was used to compare antibody positive and antibody negative group. Results: Out of 31 patients with presumptive AE, 16 patients tested positive for autoimmune antibodies (definite AE). Incidences of seizure, behavioral abnormalities, dementia and altered sensorium were similar between the 2 groups (p > 0.05). Complete or partial response was seen in all treated patients in both groups with no significant difference (p 0.716). CSF protein concentration and cellularity were higher in the definite group although only high protein concentration could reach statistical significance (p 0.002). Malignancy could be confirmed after extensive search in 2 out of 16 patients with definite AE and in 1 out of 15 antibody negative AE patients. Conclusions: Clinical presentation of antibody negative cases does not differ significantly from definite ones. Since treatment response is also similar in both the groups, starting immunotherapy in a patient presenting with presumptive symptoms of AE, while ruling out other common mimickers, seems to be the need of the hour in the management of this evolving entity.