Acquired neuromyotonia: A new autoantibody-mediated neuronal potassium channelopathy

Neuromyotonia (Isaacs syndrome) is a rare and heterogenous syndrome of cont inuous motor unit activity of peripheral nerve origin that manifests as var ious combinations of muscle stiffness, cramps, twitching, weakness, and del ayed muscle relaxation. Although neuromyotonia may accompany an assortment of inherited diseases, most cases are acquired. The observation that the ac quired form is often associated with an autoimmune disorder, and the demons tration that some cases improve after plasma exchange, has led to a search for an immune-mediated etiology. This review summarizes the recent immunolo gical and electrophysiological evidence that autoantibodies to voltage-gate d potassium channels produce the peripheral motor nerve hyperexcitability t hat characterizes neuromyotonia and thus establishes acquired neuromyotonia as an autoantibody-mediated disorder. In the nervous system, ion channels and neurotransmitter receptors that function as ligand-gated ion channels s eem to be favored targets for autoantibody attack, and neuromyotonia can no w be added to the growing list of autoimmune channelopathies.