Neurological diseases associated with autoantibodies targeting the voltage-gated potassium channel complex: immunobiology and clinical characteristics

Voltage-gated potassium channels (VGKCs) represent a group of tetrameric signaling proteins with several functions, including modulation of neuronal excitability and neurotransmitter release. Moreover, VGKCs give a key contribution to the generation of the action potential. VGKCs are complexed with other neuronal proteins, and it is now widely known that serum autoantibodies directed against VGKCs are actually directed against the potassium channel subunits only in a minority of patients. By contrast, these autoantibodies more commonly target three proteins that are complexed with alpha-dendrotoxin-labeled potassium channels in brain extracts. These three proteins are contactin-associated protein-2 (Caspr-2), leucine-rich, glioma inactivated 1 (LGI-1)-protein and the protein Tag-1/contactin-2. Neoplasms are detected only in a minority of seropositive patients for VGKC complex-IgG and do not significantly associate with Caspr-2 or LGI-1. Among all the cancers described in association with VGKC complex-IgG, lung carcinoma, thymoma, and hematologic malignancies are the most commonly detected. We will review all the major neurological conditions associated with VGKC complex-IgG. These include Isaacs’ syndrome, Morvan syndrome, limbic encephalitis, facio-brachial dystonic seizures, chorea and other movement disorders, epilepsy, psychosis, gastrointestinal neuromuscular diseases, a subacute encephalopathy that mimics Creutzfeldt-Jakob prion disease both clinically and radiologically and autoimmune chronic pain. The vast majority of these conditions are reversible by immunotherapy, and it is becoming increasingly recognized that early diagnosis and detection of VGKC complex-IgG is critical in order to rapidly start the treatment. As a result, VGKC complex-IgG are now part of the investigation of patients with unexplained subacute onset of epilepsy, memory or cognitive problems, or peripheral nerve hyperexcitability syndromes.