Muscle cramps

Cramp
Classification and external resources
ICD-10	R25.2
ICD-9-CM	729.82
DiseasesDB	3151
MedlinePlus	003193
Patient UK	Cramp
MeSH	D009120
[]

A cramp is a sudden, involuntary muscle contraction or over-shortening; while generally temporary and non-damaging, they can cause mild-to-excruciating pain, and a paralysis-like immobility of the affected muscle(s). Onset is usually sudden, and it resolves on its own over a period of several seconds, minutes, or hours. Cramps may occur in a skeletal muscle or smooth muscle. Skeletal muscle cramps may be caused by muscle fatigue or a lack of electrolytes (e.g., low sodium, low potassium, or low magnesium, although the evidence has been mixed). Cramps of smooth muscle may be due to menstruation or gastroenteritis.

Causes of cramping includehyperflexion, hypoxia, exposure to large changes in temperature, dehydration, or low blood salt. Muscle cramps can also be a symptom or complication of pregnancy; kidney disease; thyroid disease; hypokalemia, hypomagnesemia, or hypocalcaemia (as conditions); restless legs syndrome; varicose veins; and multiple sclerosis.

Electrolyte disturbance may cause cramping and muscle tetany, particularly hypokalemia and hypocalcaemia. This disturbance arises as the body loses large amounts of interstitial fluid through sweat. This interstitial fluid comprises mostly water and salt (sodium chloride). The loss of osmotically-active particles outside of muscle cells leads to a disturbance of the osmotic balance and therefore shrinking of muscle cells, as these contain more osmotically-active particles. This causes the calcium pump between the muscle sarcoplasm and sarcoplasmic reticulum to "short circuit"; the calcium ions remain bound to the troponin, continuing muscle contraction.

...
Wikipedia