Cramp
Co-Editor-In-Chief: Elliot B. Tapper, M.D., Department of Medicine, Beth Israel Deaconess Medical Center;
Co-Editor-In-Chief: C. Michael Gibson, M.S., M.D.

# Overview
Cramps are unpleasant, often painful, sensations caused by contraction or over shortening of muscles.  Cramps have many causes - from overexertion to imbalances of electrolytes (e.g. calcium)or more complex conditions. They can be fleeting or disabling. Cramps can occur in virtually any muscle-bound organ. This is a broad overview of all muscular cramps.

# Classification

## Nocturnal Leg Cramps
Nocturnal leg cramps are involuntary, often very painful muscle contractions that occur in the calves, soles of the feet, or other muscles in the body during the night or (less commonly) while resting. The duration of nocturnal leg cramps is highly variable with cramps sometimes only lasting a few seconds and other times several minutes. Soreness in the muscles may remain for some time after the cramp ends. These leg cramps are a common occurrence in late-term pregnancy and frequently afflict patients cirrhosis and those on dialysis. Most cramps, however, occur outside the context of systemic disease. These cramps are more common in older people but may happen to anyone. In population studies in the Netherlands and Sweden, 36% of all adults reported one or more disabling cramps per year and 2% report weekly cramps. As many as 50-60% of Americans over the age of 65 complain of more than one disabling muscle cramp per week.
The precise cause of these cramps is unclear. Potential contributing factors are believed to include dehydration, low levels of certain minerals (magnesium, potassium, calcium, and sodium), and the reduced blood flow through the muscles attendant in prolonged sitting or lying down.  An important cause specific to nocturnal leg cramps is iron deficiency. Through an unknown mechanism, low levels of iron can result in occasional or disabling cramps. It can often manifest as the so-called Restless Legs Syndrome of irresistible nocturnal movement impulses that resolve with standing or walking around. Anyone seeking evaluation for cramps or restless legs should have their hemoglobin or iron levels checked as iron repletion will improve and, often, stop the cramps altogether. There is no role, however, for iron supplementation in patients with a normal ferritin level.
The treatment of cramps can be difficult; there is very sparse data in the literature guiding treatment decisions. The medication with the best data support its use is Quinine, whose effects have been known since the 1940's and are both significant and long lasting. However, Quinine is exceptionally toxic, famously causing Thrombotic Thrombocytopoenic Purpura (TTP), and has been pulled off of the market for this indication.
There are some measures which have been studied and found to be ineffective: stretching, magnesium, vitamin E and gabapentin have all been evaluated with no benefit. Some measures are used by clinicians, but have never been formally evaluated by trial: baclofen, carbamazepine, and oxcarbazepine. Finally, there are a few medications that have proven benefit with small trial data: injected lidocaine (however impractical), vitamin B6, verapamil and diltiazem.

## Smooth Muscle Cramps
Smooth muscle contractions lie at the heart of the cramping (or colicky) pain of internal organs.  These include the intestine, uterus, ureter (in kidney stone pain), and various others.

### Menstrual Cramps
Menstruation is also highly likely to cause cramps of varying severity in the abdomen that may radiate to the lower back and thighs. Menstrual cramps can be treated with ibuprofen, acetaminophen or paracetamol, stretching exercises, or the application of heat through such means as warm baths or heating pads. Menstrual cramps that do not respond to self-treatment can be a symptom of endometriosis or other health problems.

## Skeletal Muscle Cramps
Skeletal muscles are muscles that can be voluntarily controlled. Of the skeletal muscles, those which cramp the most often are the calves, thighs, and arches of the foot. These cramps are seemingly associated with strenuous activity and can be intensely painful.

### Self Induced  Cramp
Self-induced cramp is brought on purposefully by individuals for the purpose of stretching muscle in a position where standing or greater movement is difficult or impossible. For instance, certain  workers or craftsmen may find inducing cramp in the lower legs enables them to stretch desirable muscle groups without the need to physically stand in tight spaces.

## Iatrogenic Causes
Statins are known to cause myalgia and cramps among other side effects. Additional factors increasing probability for this adverse side effects are physical exercise, age, female gender, history of cramps and hypothyroidism. Up to 80% of athletes using statins suffer significant muscular adverse effects including cramps , the rate appears to be approximately 10-25% in typical population using statins . In some cases this adverse effects will disappear after switching to a different statin, however they should not be ignored if they persist as they can rarely develop into a more serious problem. Coenzyme Q10 supplementation can be helpful to avoid some statin related adverse effects but currently there is not enough evidence to prove effectiveness in avoiding myopathy or myalgia .

# Causes
There are numerous causes of cramping: hyperflexion; inadequate oxygenation; exposure to large changes in temperature; dehydration; low blood salt; or low blood calcium. Muscle cramps may also be a symptom/complication of pregnancy, kidney disease, thyroid disease, severe hypokalemia or hypocalcemia, restless legs syndrome, and neurologic disorders like multiple sclerosis or ALS. Cramps can also occur 'idiopathically' with no apparent cause.
Electrolyte disturbance may cause cramping and tetany of muscles, particularly critical hypokalaemia (a low level of potassium) and hypocalcaemia (a low level of calcium). This disturbance arises as the body loses large amounts of interstitial fluid through sweat. This interstitial fluid is composed mostly of water and table salt (NaCl). The loss of osmotically active particles outside muscle cells(NaCl) leads to a disturbance of the osmotic balance and swelling of muscle cells as these contain more osmotically active particles. This causes the calcium pump between the muscle lumen and sarcoplasmic reticulum to short circuit and the calcium ions remain bound to the tropomyosin and the muscle contraction is  continued. This may occur when the lactic acid is high in the cells.

## Causes by Organ System

## Causes in Alphabetical Order

# Treatment
Muscle cramps can be treated by applying a soft massage on the cramped muscle, stretching the muscle and applying heat or cold. Heat improves superficial blood circulation and makes muscles more flexible, so some people find that heat is more soothing for muscle cramps. Application of excessive heat or cold to sore muscles may bring on cramps. Pounding on a cramped muscle can increase soreness.
- In the case of inadequate oxygenation, excess lactic acid, produced by anaerobic respiration, builds up and stresses the muscle. In addition to the methods described above, cramps from poor oxygenation can be improved by rapid deep breathing.
- Cramps from lack of water and/or salt can be treated by drinking water and/or increasing salt intake, respectively.
There is no scientific evidence to support the widely held claim by the sports nutrition industry that intake of specially composed electrolyte drinks has any advantage over intake of plain table salt (via drink or food) and water to counter these electrolyte disturbances and muscle cramps in people with a well-functioning renal system.
Eating foods high in potassium can help prevent muscle cramps.  Foods with high sources of potassium include, in order from highest to lowest: avocados, potatoes, bananas, broccoli, orange juice, soybeans and apricots, although it is also common in most fruits, vegetables and meats.
Leg cramps may also be due to vitamin D deficiency (also needed for calcium absorption). Due to change in diet, shunning milk because of high cholesterol content, or, in children, preference for soft drinks, and decreased sun exposure, vitamin D deficiency is widespread. Correcting this deficiency will in many cases also eliminate, or reduce, frequency of leg cramps.

# Related Chapters
- Trigger points
- Side Stitch
- Delayed onset muscle soreness