Management of voltage-gated potassium channel antibody disorders.

Syndromes from antibodies to voltage-gated potassium channels include neuromyotonia (NMT), limbic encephalitis (LE) and Morvan syndrome (MVS). There are distinct clinical features for NMT (cramps, stiffness, fasciculations, myokymia, hyperhidrosis; afterdischarges and continuous motor activity on electromyogram), LE (encephalopathy with seizures, deficient recent memory; hyponatremia, temporal lobe magnetic resonance imaging and electroencephalographic abnormalities) and MVS (NMT plus hyperhidrosis, dysautonomia, encephalopathy, severe insomnia, and sleep disorders). There may be associated myasthenia gravis or thymoma, and rarely lung cancer (small cell or adenocarcinoma), mandating that chest imaging be part of the evaluation. Most cases respond favorably to immunosuppression with plasma exchange, intravenous immunoglobulin or pulse intravenous methylprednisolone, usually followed by oral steroids.