[Limbic encephalitis: a probably under-recognized syndrome].

Limbic encephalitis was identified as a clinicopathological entity in 1968. Up to a few years ago, 200 cases were described, most associated with lung cancer and more infrequently with other tumors. The recent identification of patients with this syndrome, idiopathic limbic encephalitis, who never develop cancer and have high titers of antibodies to voltage-gated potassium channels (VGKC) and an excellent response to immunosuppressive therapy, has extended the etiological spectrum and suggests that the syndrome may be under-recognized. The disorder, which develops in a few days or weeks, is characterized by the development of short-term memory loss, seizures, confusion and psychiatric features. The presence of symptoms beyond the limbic system is highly suggestive of a paraneoplastic origin. When limbic encephalitis is suspected, the following tests should be performed in order to demonstrate: a) involvement of the temporal lobes (EEG and brain MRI); b) presence of inflammatory abnormalities in the CSF, and c) the presence of onconeural antibodies or anti-VGKC. Once the diagnosis is confirmed by the clinical picture and MRI findings, treatment must be initiated without waiting for the antibody results because its negativity does not exclude the diagnosis. Detection of an onconeural antibody will confirm that the limbic syndrome is paraneoplastic and will help us to search for an underlying tumor and to predict possible response to the treatment. The recommended treatment is cycles of methylprednisolone (1 g/day for 3 to 5 days). Therapeutic response in the idiopathic limbic encephalitis is excellent and may be good in limbic encephalitis with anti-Ma2 or without onconeural antibodies. On the contrary, immunosuppressant treatment is not usually effective in limbic encephalitis associated to anti-Hu antibodies.