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.