[Isaacs' syndrome. Diagnosis and differential diagnosis of neuromyotonia]

Neuromyotonia is a clinical and electrophysiological syndrome of spontaneous muscle fiber activity due to hyperexcitability of peripheral nerve origin causing generalised, visible myokymia and muscular cramps. Electromyography shows abnormal doublet and triplet discharges of high intraburst frequency as well as myokymic and neuromyotonic discharges. Fasciculations and fibrillation potentials are common. Most commonly, neuromyotonia is an acquired immune-mediated disorder (Isaacs' syndrome) showing elevated antibody levels against presynaptic, voltage-gated, potassium channels. Some of these patients have additional autonomic (hyperhidrosis) and/or CNS symptoms similar to those from limbic encephalitis (referred to then as Morvan's syndrome). We report on a patient with Isaacs' syndrome and discuss the clinical and electrophysiological features, pathophysiology, diagnosis, and differential diagnosis of diseases with peripheral nerve hyperexcitability.