Causes
It may be acquired and or inherited, and is caused by an abnormality in the muscle membrane—specifically, the ion channels that controls the contraction of muscle fibers. 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 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.
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