Neuromyotonia
|
|
Neuromyotonia is spontaneous muscular activity resulting from repetitive motor unit action potentials of peripheral origin. 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. cerebellar ataxia, 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. Moreover, these antibodies have been demonstrated to reduce potassium channel function in neuronal cell lines.
As a result of muscular hyperactivity patients may present with muscle cramps, myotonia like symptoms, excessive sweating, myokimia 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.