Neuromyotonia

Neuromyotonia
Specialty	Neurology, neuromuscular medicine

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

Causes

NMT is a form of Peripheral Nerve Hyperexcitability (PNH). 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/Symptoms

As a result of muscular hyperactivity patients may present with muscle cramps, stiffness, myotonia-like symptoms (slow relaxation), excessive sweating, myokymia (quivering of a muscle), fibrillation (rapid twitching of individual muscle fibers with litle or no movement of the muscle as a whole), fasciculations (coarser form of muscular contraction,consisting on involuntary contraction of bunches of muscle fibers), fatigue, exercise intolerance and other related symptoms. The symptoms (especially the stiffnes and fasciculations) are most prominent in the calves, legs, trunk, and sometimes the face and neck, but can also affect other body parts.

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 may provide short-term relief for patients with some forms of the acquired disorder. Botox injections also provide short-term relief.

Prognosis

The long-term prognosis for individuals with the disorder is uncertain, and this has mostly to do with the etiology (underlying cause; i.e. autoimmune, paraneoplastic, etc) and lack of research for this disorder. However, in recent years our 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. ^[2]. Many patients respond well to treatment, which usually provide significant relief of symptoms. Some cases of spontaneous remission have been noted, including the original two subjects from Isaacs' original paper when followed up 14 years later.

This condition is not fatal; however it does mimic symptoms of motor neuron disease, which is fatal. This can often lead to significant anxiety until diagnosis is made. NMT symptoms may fluctuate but they generally don't deteriorate into anything more serious and with the correct treatment the symptoms are manageable.

A very small proportion of cases with NMT 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. However, this is a separate disorder.

Also, some studies have linked NMT with certain types of cancers, mostly lung and thymus, suggesting that NMT may be paraneoplastic in some cases. However, most cases of NMT is autoimmune and not associated with cancer.

References

External links

• http://isaacsyndrome.proboards.com
• http://pnhinfo.com