Role of the pathologist in the diagnosis of autoimmune encephalitis

Autoimmune encephalitis is a group of non-infectious immune-mediated inflammatory disorders manifesting with epilepsy and encephalitis syndromes that are associated with autoantibodies in the serum and/or cerebrospinal fluid (CSF). Pathogenic autoantibodies have been discovered against intracellular onconeural antigens, surface neuronal, or synaptic antigens with distinctive pathogenesis that underlie differences in response to immunotherapy. The onconeural antigens incite cytotoxic T-cell-mediated neuronal destruction, whereas surface antigens trigger direct damage by autoantibodies via complement mediated pathways, and hence respond well to immunomodulatory therapy, in contrast to poor response in the former. Neuroimaging, electroencephalogram, and CSF findings being non-specific, detection of autoantibodies is essential for a confirmatory diagnosis. Detection methods available include tissue-based assay, cell-based assays, immunoblot, cell culture, flow cytometry, and enzyme-linked immunosorbent assays. In this review, we discuss the various testing modalities available for onconeural and cell surface antibodies, their sensitivity and specificity and the emerging role of the pathologist in the diagnosis of autoimmune encephalitis. Early diagnosis is crucial for instituting treatment and preventing morbidity and mortality.