Limbic Encephalitis

Limbic encephalitis is characterized by the subacute onset, usually <3 months, of memory and cognitive deficits, behavioural changes, and seizures. The most typical deficit is impairment of short-term memory. Brain MRI shows FLAIR and T2 signal abnormalities involving bilaterally, less frequently unilaterally, the hippocampus and amygdala. Limbic encephalitis was initially considered a paraneoplastic syndrome, but after the discovery of several immunological subtypes we now know that >60% of cases are non-paraneoplastic and usually associated to LGI1 antibodies. Paraneoplastic limbic encephalitis mainly associates with small-cell lung cancer and Hu or GABAbR antibodies, testicular seminoma and Ma2 antibodies, Hodgkin disease and mGluR5 antibodies, and thymoma and AMPAR antibodies. Limbic encephalitis may be triggered by treatment of cancer with immune checkpoint inhibitors. The response to immunotherapy and outcome vary according to the type of antibody and presence or absence of an underlying tumour. In patients with antibodies against intracellular antigens (onconeural, AK5), immunotherapy is usually ineffective. In contrast, most patients with LGI1 antibodies show substantial improvement after treatment with steroids and immunotherapy. Patients with cancer and GABAbR or AMPAR antibodies respond better to treatment than those with the same type of cancer and onconeural antibodies, and worse than those of patients with LGI antibodies.