Myotonia
Encyclopedia
Myotonia is a symptom of a small handful of certain neuromuscular disorders characterized by the slow relaxation of the muscles after voluntary contraction or electrical stimulation. Generally, repeated effort is needed to relax the muscles, and the condition improves after the muscles have warmed up. However, prolonged, rigorous exercise may also trigger the condition. Individuals with the disorder may have trouble releasing their grip on objects or may have difficulty rising from a sitting position and a stiff, awkward gait.
Myotonia can affect all muscle groups; however, the pattern of affected muscles can vary depending on the specific disorder involved.
People suffering from disorders involving myotonia can have a life-threatening reaction to certain anaesthetics; one of these conditions occurs when the patient is under anaesthetic and is termed "Malignant hyperthermia
".
is defective in myotonia. Myotonia is a symptom commonly seen in patients with myotonic muscular dystrophy
, of which two documented types and one speculated type exist, and in a group of disorders called channelopathies
(hereditary diseases that are caused by mutations in the chloride, sodium or potassium ion transport channels in the muscle membrane), such as Myotonia Congenita (Congenital Myotonia) of which two types called Becker's Disease and Thomsen's Disease exist. There is also a disorder called Paramyotonia Congenita. Myotonia arises from channelopathies, and myotonic muscular dystrophy can be exacerbated by exposure to cold (and occasionally heat); by eating foods that are potassium-rich (such as bananas); with exertion, especially after long periods of inactivity; sudden surprises; and stressful situations.
Symptoms of myotonia are more frequently experienced in women during pregnancy.
Myotonia is not always a disease-related or abnormal phenomenon. Humans and other animals (such as the fainting goat
) often display myotonia when placed in situations of extreme stress or fear; a resultant increase in 'fight-or-flight' hormones such as epinephrine
and cortisol
may cause increased muscle tension throughout the body.
Myotonia can affect all muscle groups; however, the pattern of affected muscles can vary depending on the specific disorder involved.
People suffering from disorders involving myotonia can have a life-threatening reaction to certain anaesthetics; one of these conditions occurs when the patient is under anaesthetic and is termed "Malignant hyperthermia
Malignant hyperthermia
Malignant hyperthermia or malignant hyperpyrexia is a rare life-threatening condition that is usually triggered by exposure to certain drugs used for general anesthesia; specifically, the volatile anesthetic agents and the neuromuscular blocking agent, succinylcholine...
".
Causes
It may be acquired or inherited, and is caused by an abnormality in the muscle membrane--specifically, the ion channels that control the contraction of muscle fibers. MyosinMyosin
Myosins comprise a family of ATP-dependent motor proteins and are best known for their role in muscle contraction and their involvement in a wide range of other eukaryotic motility processes. They are responsible for actin-based motility. The term was originally used to describe a group of similar...
is defective in myotonia. Myotonia is a symptom commonly seen in patients with myotonic muscular dystrophy
Myotonic dystrophy
Myotonic dystrophy is a chronic, slowly progressing, highly variable inherited multisystemic disease. It is characterized by wasting of the muscles , cataracts, heart conduction defects, endocrine changes, and myotonia. Myotonic dystrophy can occur in patients of any age...
, of which two documented types and one speculated type exist, and in a group of disorders called channelopathies
Channelopathy
Channelopathies are diseases caused by disturbed function of ion channel subunits or the proteins that regulate them. These diseases may be either congenital or acquired .There are a large number of distinct dysfunctions known to be caused by ion channel...
(hereditary diseases that are caused by mutations in the chloride, sodium or potassium ion transport channels in the muscle membrane), such as Myotonia Congenita (Congenital Myotonia) of which two types called Becker's Disease and Thomsen's Disease exist. There is also a disorder called Paramyotonia Congenita. Myotonia arises from channelopathies, and myotonic muscular dystrophy can be exacerbated by exposure to cold (and occasionally heat); by eating foods that are potassium-rich (such as bananas); with exertion, especially after long periods of inactivity; sudden surprises; and stressful situations.
Symptoms of myotonia are more frequently experienced in women during pregnancy.
Myotonia is not always a disease-related or abnormal phenomenon. Humans and other animals (such as the fainting goat
Fainting goat
A fainting goat is a breed of domestic goat whose muscles freeze for roughly 10 seconds when the goat is startled. Though painless, this generally results in the animal collapsing on its side. The characteristic is caused by a hereditary genetic disorder called myotonia congenita. When startled,...
) often display myotonia when placed in situations of extreme stress or fear; a resultant increase in 'fight-or-flight' hormones such as epinephrine
Epinephrine
Epinephrine is a hormone and a neurotransmitter. It increases heart rate, constricts blood vessels, dilates air passages and participates in the fight-or-flight response of the sympathetic nervous system. In chemical terms, adrenaline is one of a group of monoamines called the catecholamines...
and cortisol
Cortisol
Cortisol is a steroid hormone, more specifically a glucocorticoid, produced by the adrenal gland. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat,...
may cause increased muscle tension throughout the body.
See also
- Myotonia congenitaMyotonia congenitaCongenital myotonia is a genetic, neuromuscular channelopathy that affects skeletal muscles . It is congenital, meaning that it is present from birth. Amongst other problems, it causes delayed relaxation of the muscles and rigidity...
- Potassium-aggravated myotoniaPotassium-aggravated myotoniaPotassium-aggravated myotonia is a rare genetic disorder that affects skeletal muscle. Beginning in childhood or adolescence, people with this condition experience bouts of sustained muscle tensing that prevent muscles from relaxing normally...
- Myotonic dystrophyMyotonic dystrophyMyotonic dystrophy is a chronic, slowly progressing, highly variable inherited multisystemic disease. It is characterized by wasting of the muscles , cataracts, heart conduction defects, endocrine changes, and myotonia. Myotonic dystrophy can occur in patients of any age...
- Fainting goatFainting goatA fainting goat is a breed of domestic goat whose muscles freeze for roughly 10 seconds when the goat is startled. Though painless, this generally results in the animal collapsing on its side. The characteristic is caused by a hereditary genetic disorder called myotonia congenita. When startled,...