Antibodies to voltage gated potassium channels in encephalitis

Background: Raised levels of antibodies to voltage gated potassium channels (VGKC) have been found in acquired neuromyotonia, Morvan's syndrome (neuromyotonia with CNS involvement), and two patients with limbic syndromes. It is not yet clear how frequently VGKC antibodies are present in patients with CNS disorders, whether neuromyotonia is always present, or whether they signify a good response to immunomodulation.

Methods: Eleven serum samples from patients with unusual adult onset epilepsy syndromes and/or unexplained encephalitic/psychotic symptoms presenting to a general neurology clinic were screened for VGKC antibodies. Results were compared with sera from healthy and disease controls.

Results: Five of 11 sera were positive at levels between 150 and 1050 pM (controls <100 pM). The clinical syndromes included: late onset myoclonic epilepsy with cognitive impairment and improvement with plasma exchange; limbic encephalitis with focal siezures; Hashimoto's encephalitis; intractable epilepsy and hypogammaglobulinaemia; and an acute onset of personality change and psychosis. Neuromyotonia was not evident clinically, and was excluded by electrophysiology in one patient.

Discussion: VGKC antibodies appear relatively common in patients with unexplained encephalitic illnesses, but not necessarily neuromyotonia. The lack of such antibodies in other CNS controls and a response to plasma exchange in one of two patients suggests these antibodies may be pathogenic.