NORD is very grateful to Matthew Kiernan, PhD, DSc, Bushell Chair of Neurology, Brain & Mind Research Institute, The University of Sydney, for assistance in the preparation of this report.
Synonyms of Acquired Neuromyotonia
- continuous muscle fiber activity syndrome
- Isaacs-Merten Syndrome
- Isaacs' Syndrome
- quantal squander
- No subdivisions found.
Acquired neuromyotonia is an inflammatory disorder characterized by abnormal nerve impulses from the peripheral nerves that result in continuous muscle fiber activity. Affected individuals often experience progressive muscle stiffness and cramping especially in the hands and feet, increased sweating, and delayed muscle relaxation. Symptoms may persist even during sleep or under general anesthesia.
Acquired neuromyotonia is characterized by involuntary continuous muscle fiber activity (fasciculations) that cause stiffness and delayed relaxation in the affected muscles. Muscle twitching with a rippling appearance (myokymia) may occur along with these symptoms. Affected individuals may, at times, be unable to coordinate voluntary muscle movement and find difficulty in walking (ataxia). Other symptoms may include staggering and reeling (titubation), stiffness, and lack of balance in response to being startled. There may be diminished spontaneous gross motor activity.
The disorder is characterized by progressive stiffness, cramping, and weakness. Muscle activity is constant, and patients describe the feeling of continuous writhing or rippling of muscles under the skin. These movements continue during sleep. Diminished reflexes are also frequently a sign of this disorder. In some instances, muscle relaxation following voluntary muscle movement is delayed (grip myotonia) in the affected muscles. For example, affected individuals may be not be able to open their fists or eyes immediately after closing them tightly for a few seconds.
Affected individuals frequently have excessive sweating (hyperhidrosis), rapid heartbeats (tachycardia) and weight loss.
In slightly fewer than 20% of the cases, a set of symptoms, including arrhythmias, excessive salivation, memory loss, confusion, hallucinations, constipation, personality change and/or sleep disorders, are found. In such cases the disorder may be referred to as Morvan syndrome.
Approximately 20% of affected individuals have a tumor of the thymus gland (thymoma). The thymus glands are the source of a number of specialized cells associated with autoimmune functions. The disorder is also associated with peripheral neuropathies and autoimmune diseases including myasthenia gravis in some individuals. It has also been reported following infections and radiation therapy.
Acquired neuromyotonia is an autoimmune disease in which the immune system malfunctions so that it damages parts of one's own body. Approximately 40% of affected individuals have antibodies to voltage-gated potassium channels (VGKC's) that affect the points at which the signals from the nerve fiber meet the muscle cell (neuromuscular junction).
Aquired neuromyotonia is a rare disorder affecting males and females but is slightly more common among men. Disease onset is usually between the ages of 15 and 60 years but has also been reported in childhood.
Symptoms of the following disorders can be similar to those of acquired neuromyotonia. Comparisons may be useful for a differential diagnosis:
Amyotrophic lateral sclerosis (ALS) is one of a group of disorders known as motor neuron diseases. It is characterized by the progressive degeneration and eventual death of nerve cells (motor neurons) in the brain, brainstem and spinal cord that facilitate communication between the nervous system and voluntary muscles of the body. Ordinarily, motor neurons in the brain (upper motor neurons) sent messages to motor neurons in the spinal cord (lower motor neurons) and then to various muscles. ALS affects both the upper and lower motor neurons, so that the transmission of messages is interrupted, and muscles gradually weaken and waste away. As a result, the ability to initiate and control voluntary movement is lost. Ultimately, ALS leads to respiratory failure because affected individuals lose the ability to control muscles in the chest and diaphragm. ALS is often called Lou Gehrig's disease. (For more information on these disorders, choose "ALS" as your search terms in the Rare Disease Database.)
Neurodegeneration with Brain Iron Accumulation Type 1 (Hallervorden-Spatz syndrome) is a rare, inherited, neurological movement disorder characterized by the progressive degeneration of the nervous system (neurodegenerative disorder). Individuals with NBIA1 have iron accumulation in the brain along with a progressive movement disorder. Individuals can plateau for long periods of time and then undergo intervals of rapid deterioration. Symptoms may vary greatly from case to case. Common features include an abnormality in muscle tone (dystonia), muscular rigidity, and sudden involuntary muscle spasms (spasticity). These features can result in clumsiness, walking problems, difficulty controlling movement, and speech problems. Another common feature is degeneration of the retina, resulting in progressive night blindness and loss of peripheral (side) vision. Approximately 50% of individuals with a clinical diagnosis of NBIA1 have gene mutations in PANK2, which helps to metabolize vitamin B5. (For more information on these disorders, choose "NBIA" as your search terms in the Rare Disease Database.)
Hereditary spastic paraplegia (HSP) is a group of inherited neurological disorders characterized by progressive weakness (paraplegia), increased muscle tone and spasticity of leg muscles. The age of onset and severity of symptoms may be extremely variable from case to case, including among individuals within the same family. Symptoms usually develop during early to mid-adulthood. Initial findings typically include stiffness and relatively mild weakness of leg muscles, balance difficulties, unexplained tripping and falls, and an unusually "clumsy" manner of walking. As the disorder progresses, walking may become increasingly difficult, however, complete loss of the ability to walk is relatively rare. (For more information on this disorder, choose "paraplegia" as your search term in the Rare Disease Database.)
Stiff-person syndrome (SPS) is a rare acquired neurological disorder characterized by progressive muscle stiffness (rigidity) and repeated episodes of painful muscle spasms. Muscular rigidity often fluctuates and usually occurs along with the muscle spasms. Spasms may occur randomly or be triggered by a variety of different events including a sudden noise or light physical contact. In most cases, other neurological signs or symptoms do not occur. The severity and progression of SPS varies from one person to another. If left untreated, SPS can potentially progress to cause difficulty walking and significantly impact a person's ability to perform routine, daily tasks. Although the exact cause of SPS is unknown, it is believed to be an autoimmune disorder and sometimes occurs along with other autoimmune disorders. (For more information on this disorder, choose "SPS" as your search term in the Rare Disease Database.)
Episodic ataxia type 1(EA1) is an autosomal dominant genetic disorder characterized by muscle cramps and stiffness; muscle twitching with a rippling appearance; spastic contraction of skeletal muscles of the head, arms and legs; and loss of motor coordination and balance. EA1 is caused by mutations in the KCNA1 gene.
The diagnosis of acquired neuromyotonia is based on the presence of continuous muscle contractions (myokymia), especially in the face and hands, rhythmic tics or twitches (fasciculations), and muscle cramps. The diagnosis is confirmed by studies of the electrical signs of muscle activity (electromyography).
Acquired neuromyotonia may be treated with anticonvulsant drugs such as phenytoin or carbamazepine, which may stop the abnormal impulses and prevent the symptoms from reoccurring. Plasma exchange (plasmapheresis) and intravenous immune globulin have been effective in a few cases but no long-term, controlled, clinical studies have been carried out.
Testing for acetylcholine receptor antibodies should be done if thymoma is suspected. The thymus gland should be surgically removed if thymoma is present.
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.
For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:
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Organizations related to Acquired Neuromyotonia
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NINDS Isaac's syndrome Information Page. Last Updated February 8, 2013.
www.ninds.nih.gov/health_and_medical/disorders/isaacs_syndrome.htm Accessed Jan 22, 2014.
D’Adamo MC, Hanna MG, Di Giovanni G, et al. Episodic Ataxia Type 1. 2010 Feb 9 [Updated 2012 Aug 16]. In: Pagon RA, Adam MP, Bird TD, et al., editors. GeneReviews[Internet]. Seattle (WA): University of Washington, Seattle; 1993-2014. Available from: http://www.ncbi.nlm.nih.gov/books/NBK25442/ Accessed Jan 22, 2014.
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