Ion channel and striational antibodies define a continuum of autoimmune neuromuscular hyperexcitability

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Abstract
Neuromuscular hyperexcitability is a characteristic of Isaacs' syndrome. Autoantibodies specific for voltage‐gated potassium channels (VGKC) or ganglionic nicotinic acetylcholine receptors (AChR) are markers of this disorder. To determine the frequency of these ion channel antibodies and of related neuron‐ and muscle‐specific antibodies in patients with acquired neuromuscular hyperexcitability, we tested serum specimens from 77 affected patients (35 neuromyotonia, 32 cramp‐fasciculation syndrome, 5 rippling muscle syndrome, and 5 focal neuromuscular hyperexcitability) and 85 control subjects. Among study patients, 14% had coexisting myasthenia gravis, and 16% had an associated neoplasm. We found that 35% had VGKC antibodies, 12% ganglionic AChR antibodies, 16% muscle AChR antibodies, and 10% striational antibodies. Overall, 55% had serological evidence of neurological autoimmunity compared to 2% of control subjects. Patients with neuromyotonia were more frequently seropositive (71%) than patients with cramp‐fasciculation syndrome (31%). We conclude that acquired neuromuscular hyperexcitability consists of a continuum of clinical disorders with a common autoimmune pathogenesis. © 2002 Wiley Periodicals, Inc. Muscle Nerve 26: 702–707, 2002