OBSOLETE: Non-paraneoplastic limbic encephalitis

Non-paraneoplastic limbic encephalitis is a rare autoimmune neurological disorder characterized by inflammation of the limbic system of the brain, including the hippocampus, amygdala, and related structures, in the absence of an underlying malignancy. This condition has been reclassified and is now considered obsolete as a distinct Orphanet entity (Orphanet code 163918), as it has been incorporated into broader classifications of autoimmune encephalitis. The disease is mediated by autoantibodies directed against neuronal surface or intracellular antigens, including antibodies against voltage-gated potassium channel (VGKC) complex proteins such as LGI1 and CASPR2, NMDA receptors, AMPA receptors, and GABA-B receptors, among others. The condition primarily affects the central nervous system and manifests with subacute onset of short-term memory loss, confusion, seizures (often temporal lobe epilepsy), psychiatric symptoms including anxiety, depression, personality changes, and sleep disturbances. Some patients may also develop faciobrachial dystonic seizures, particularly those with LGI1 antibodies. Hyponatremia is a common associated finding in LGI1-antibody-mediated cases. MRI typically shows T2/FLAIR hyperintensities in the medial temporal lobes, and cerebrospinal fluid may show mild pleocytosis and elevated protein. Treatment involves immunotherapy, which may include first-line therapies such as corticosteroids, intravenous immunoglobulin (IVIG), and plasma exchange, as well as second-line agents including rituximab and cyclophosphamide for refractory cases. Early and aggressive immunotherapy is associated with better outcomes. Long-term immunosuppressive maintenance therapy may be required to prevent relapses. Prognosis varies depending on the specific antibody involved and the timeliness of treatment initiation, but many patients show significant improvement with appropriate immunotherapy.

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