Neuromyotonia, also known as Isaacs' Syndrome, is spontaneous muscular activity resulting from repetitive motor unit action potentials of peripheral origin.

Causes

It develops as a result of both acquired or hereditary diseases. Acquired form is more frequent and is usually caused by antibodies against neuromuscular junction.

Autoreactive antibodies can be detected in a variety of peripheral (e.g. myasthenia gravis, Lambert-Eaton myasthenic syndrome) and central nervous system (e.g. paraneoplastic cerebellar degeneration, paraneoplastic limbic encephalitis) disorders. Their causative role has been established in some of these diseases but not all. Neuromyotonia is considered to be one of these with accumulating evidence for autoimmune origin over the last few years. Some neuromyotonia cases do not only improve after plasma exchange but they may also have antibodies in their serum samples against voltage-gated potassium channels.^[1] Moreover, these antibodies have been demonstrated to reduce potassium channel function in neuronal cell lines.

Presentation

As a result of muscular hyperactivity patients may present with muscle cramps, myotonia-like symptoms, excessive sweating, myokymia and fasciculations. A very small proportion of cases with neuromyotonia may develop central nervous system findings in their clinical course, causing a disorder called Morvan's syndrome and they may also have antibodies against potassium channels in their serum samples. Sleep disorder is only one of a variety of clinical conditions observed in Morvan's syndrome cases ranging from confusion and memory loss to hallucinations and delusions.

Treatment

There is no known cure for neuromyotonia. The long-term prognosis for individuals with the disorder is uncertain. Anticonvulsants, including phenytoin and carbamazepine, usually provide significant relief from the stiffness, muscle spasms, and pain associated with neuromyotonia. Plasma exchange may provide short-term relief for patients with some forms of the acquired disorder.

References

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