Myotonia

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".

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. Myosin 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.