Peripheral Nerve Hyperexcitability - Cramp-Fasciculation Syndrome, Neuromyotonia and Morvan's Syndrome

Syndromes of peripheral nerve hyperexcitability represent a group of rare syndromes with distinct clinical and electrophysiological features. The mildest form, the cramp-fasciculation syndrome (CFS) is characterised by muscle cramps and fasciculations which are also seen on electromyographic recordings (EMG). In neuromyotonia (NMT) patients complain about cramps, fasciculations, muscle stiffness, paraesthesia and increased sweating. EMG shows typical high-frequency neuromyotonic discharges, doublets, triplets and multiplets. Features of Morvan's syndrome are neuromyotonia, dysautonomia and behavioural and cognitive changes. Antibodies against proteins which interact with voltage-gated potassium channels (Contactin-2, CASPR-2 und LGI-1) are found in up to 25, 50 and 90 % in patients with CFS, NMT and Morvan's syndrome. NMT and Morvan's syndrome can occur as paraneoplastic syndromes associated with thymoma and small-cell lung cancer. Paraneoplastic hyperexcitability disorders can respond to successful treatment of the tumour, autoimmune forms may respond to plasma exchange or intravenous immunoglobulins. Sodium channel blocking agents, e. g., carbamazepine, are used as symptomatic treatment.