Neuromyotonia

Neuromyotonia (NMT) is a form of peripheral nerve hyperexcitability that causes spontaneous muscular activity resulting from repetitive motor unit action potentials of peripheral origin. The prevalence of NMT is unknown but 100–200 cases have been reported so far. Neuromyotonia (NMT) is a form of peripheral nerve hyperexcitability that causes spontaneous muscular activity resulting from repetitive motor unit action potentials of peripheral origin. The prevalence of NMT is unknown but 100–200 cases have been reported so far. 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. The three causes of NMT are: The 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. 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. Autoimmune neuromyotonia is typically caused by antibodies that bind to potassium channels on the motor nerve resulting in continuous/hyper-excitability. Onset is typically seen between the ages of 15–60, with most experiencing symptoms before the age of 40. 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.