Autoimmune encephalitis, is a clinically challenging entity with varied neurological presentations. As autoimmune serology is negative in over 50% cases, our objective was to prioritise the use of electroencephalography supported by MRI Brain or PET – CT imaging to make a definitive diagnosis of autoimmune encephalitis. 

Autoimmune encephalitis is the consequence of an antibody mediated neuronal damage caused by cell surface antigens. However, antibody assays can be negative in early stages of the disease. Hence, we suggest the use of electroencephalogram along with MRI brain imaging or PET-CT scans to avoid diagnostic delays.   

During a span of four years [2018 – 2022] a retrospective review of the case records of 50 patients of autoimmune encephalitis and 50 patients of non-autoimmune encephalitis were compared. Besides clinical examination, serum and cerebrospinal fluid viral and autoimmune antibody assay, electroencephalogram, Magnetic Resonance and FDG-PET- CT scans were used to confirm the diagnosis.  

60% patients were seronegative and 40 % were seropositive in the autoimmune group while 90% were seropositive and 10% seronegative in the non-autoimmune encephalitis group. Electroencephalography was abnormal in all cases of autoimmune encephalitis 100% [50/50] and in 80% [40/50] cases of viral encephalitis. In autoimmune encephalitis, MRI Brain revealed evidence of limbic encephalitis in 80% cases and FDG PET-CT scans were abnormal in the remaining 20%. In non-autoimmune encephalitis, MRI Brain was abnormal in 60% cases and FDG PET-CT was abnormal in 10%. 

In seronegative autoimmune encephalitis, electroencephalographic abnormalities supported by MRI Brain imaging and PET-CT scans enabled early diagnosis in 100% cases [p value <0.001]. While in non-autoimmune encephalitis serology with electroencephalography, MRI Brain and PET-CT scans were diagnostic in 80% cases [p value <0.001]. However, as the sample size is small further studies are needed to confirm these findings.