Mimickers of autoimmune encephalitis: a literature review

Autoimmune encephalitis (AIE) is a rapid, progressive neurological disorder characterized by nervous system inflammation. While the Graus criteria are the best known criteria for AIE diagnosis, other differential diagnoses meeting the Graus criteria must be considered before management. This narrative review discusses the most common etiologies that resemble AIE. We suggest routine exclusion of mimickers meeting the Graus criteria before confirming an AIE diagnosis. We reviewed 28 studies including 356 patients. The main initial diagnosis was AIE, then paraneoplastic limbic encephalitis and anti-N-methyl-D-aspartate receptor encephalitis. Only 194 patients met the possible Graus criteria. The most frequent conditions among the total population were dementia, other neurodegenerative diseases, and psychiatric and functional neurological disorders. AIE is often misdiagnosed, leading to unnecessary treatment. Despite publication of the Graus criteria, medical cases mimicking this condition are being published. Many neurological diseases entering the differential diagnosis of AIE could be excluded through a detailed history, neurological examination, laboratory analysis, and other investigations, including cerebrospinal fluid and brain magnetic resonance imaging. However, some differential diagnoses complied with the possible Graus criteria, with some having concurrent antineuronal antibodies, which were considered true mimickers. AIE diagnosis suspicion is primarily clinical, but a definitive diagnosis requires various diagnostic tools.