Neuromyotonia (NMT) is a form of peripheral nerve hyperexcitability that causes spontaneous muscular activity resulting from repetitive motor unit action potentials of peripheral origin. NMT along with Morvans syndrome are the most severe types in the Peripheral Nerve Hyperexciteability spectrum. Example of two more common and less severe syndromes in the spectrum are Cramp Fasciculation Syndrome and Benign Fasciculation Syndrome. NMT can have both hereditary and acquired (non- inherited) forms. The prevalence of NMT is unknown. Signs and symptoms
NMT is a diverse disorder. As a result of muscular hyperactivity, patients may present with muscle cramps, stiffness, myotonia-like symptoms (slow relaxation), associated walking difficulties, hyperhidrosis (excessive sweating), myokymia (quivering of a muscle), fasciculations (muscle twitching), fatigue, exercise intolerance, myoclonic jerks and other related symptoms. The symptoms (especially the stiffness and fasciculations) are most prominent in the calves, legs, trunk, and sometimes the face and neck, but can also affect other body parts. NMT symptoms may fluctuate in severity and frequency. Symptoms range from mere inconvenience to debilitating. At least a third of people also experience sensory symptoms. Causes
The three causes of NMT are:
Acquired
Paraneoplastic
HereditaryThe acquired form is the most common, accounting for up to 80 percent of all cases and is suspected to be autoimmune-mediated, which is usually caused by antibodies against the neuromuscular junction. The exact cause is unknown. However, 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.
However, some objective EMG criteria have been established to help distinguish between the three. Moreover, the generic use of the term peripheral nerve hyperexcitability syndromes to describe the aforementioned conditions is recommended and endorsed by several prominent researchers and practitioners in the field. Treatments
There is no known cure for neuromyotonia, but the condition is treatable. Anticonvulsants, including phenytoin and carbamazepine, usually provide significant relief from the stiffness, muscle spasms, and pain associated with neuromyotonia. Plasma exchange and IVIg treatment may provide short-term relief for patients with some forms of the acquired disorder. It is speculated that the plasma exchange causes an interference with the function of the voltage-dependent potassium channels, one of the underlying issues of hyper-excitability in autoimmune neuromyotonia. Botox injections also provide short-term relief. Immunosuppressants such as Prednisone may provide long term relief for patients with some forms of the acquired disorder. Prognosis
The long-term prognosis is uncertain, and has mostly to do with the underlying cause; i.e. autoimmune, paraneoplastic, etc. However, in recent years increased understanding of the basic mechanisms of NMT and autoimmunity has led to the development of novel treatment strategies. NMT disorders are now amenable to treatment and their prognoses are good. Many patients respond well to treatment, which usually provide significant relief of symptoms. Some cases of spontaneous remission have been noted, including Isaacs original two patients when followed up 14 years later. While NMT symptoms may fluctuate, they generally dont deteriorate into anything more serious, and with the correct treatment the symptoms are manageable.