Potentially reversible autoimmune limbic encephalitis with neuronal potassium channel antibody

Objectives: To describe the clinical features and coexisting serum autoantibodies in seven patients with encephalitis associated with autoantibodies to α-dendrotoxin-sensitive voltage-gated potassium channels (VGKCs), and to compare this disorder with other autoimmune encephalopathies. Methods: Clinical information was obtained from a retrospective review of medical records and telephone interviews. All autoantibody testing was performed in a single laboratory. Results: The seven patients were examined for subacute cognitive and behavioral changes. Seizures, usually temporal-onset complex partial type, were documented in six patients, and all seven patients had EEG abnormalities. None had symptoms or signs of neuromuscular hyperexcitability. One described hypersalivation. Four patients had additional autoantibody markers of neurologic autoimmunity (muscle acetylcholine receptor, striational, P/Q-type calcium channel, or GAD65), and two had thyroperoxidase antibodies. Two patients had a history of cancer: one had active prostate adenocarcinoma, and the second had a remote history of tongue carcinoma. Cranial MRI demonstrated mesial temporal lobe abnormalities in all patients. One patient improved spontaneously, and six were treated with IV methylprednisolone. Three improved remarkably with treatment. At follow-up evaluation, one had no cognitive deficits, four had mild persistent short-term memory dysfunction, and two had persistent disabling behavioral deficits. Conclusions: Voltage-gated potassium channel antibodies are a valuable serologic marker of a potentially reversible autoimmune encephalopathy. The neurologic manifestations of this disorder are indistinguishable from paraneoplastic limbic encephalitis but are distinct from Morvan syndrome and Hashimoto encephalopathy.