A cramp is a sudden, brief, unintended (involuntary), and usually painful contraction of a muscle or group of muscles. Muscle cramps can be a symptom of nervous system malfunction.
Causes
The most common causes of muscle cramps are
Muscle cramps (also called charley horses) often occur in healthy people, usually in middle-aged and older people but sometimes in younger people. Cramps tend to occur during or after vigorous exercise but sometimes occur during rest. Some people have painful leg cramps during sleep. Sleep-related leg cramps usually affect the calf and foot muscles, causing the foot and toes to curl downward. Although painful, these cramps are usually not serious and are thus called benign leg cramps.
Almost everyone has muscle cramps at some time, but certain conditions increase the risk and/or severity of cramps. They include the following:
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Having tight calf muscles, which may be caused by not stretching, inactivity, or sometimes repeated accumulation of fluid (called edema) in the lower leg
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Becoming dehydrated
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Having a nerve disorder or an underactive thyroid gland (hypothyroidism)
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Taking certain drugs
Low electrolyte levels may result from use of some diuretics, alcoholism, certain hormonal (endocrine) disorders, vitamin D deficiency, or conditions that cause loss of fluids (and thus electrolytes). Electrolyte levels may become low late in pregnancy.
Cramps can occur shortly after dialysis, possibly because dialysis removes too much fluid from the body, removes the fluid too quickly, and/or lowers electrolyte levels.
Conditions That Cause or Contribute to Muscle Cramps
Category |
Examples |
Drugs |
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Use of certain drugs |
Angiotensin II receptor blockers and some beta-blockers (used to treat high blood pressure), bronchodilators (used to treat asthma), cisplatin, clofibrate, diuretics, donepezil, lovastatin, birth control pills (oral contraceptives), pyrazinamide, raloxifene, synthetic parathyroid hormone (teriparatide), tolcapone, or vincristine Stimulants, such as amphetamines, caffeine, cocaine, ephedrine, nicotine, or pseudoephedrine |
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Sudden stopping of a drug |
Sedatives, such as alcohol, barbiturates, or benzodiazepines Drugs used to treat insomnia or anxiety |
Disorders |
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Electrolyte and hormonal (endocrine) disorders |
Low levels of potassium (hypokalemia), low levels of magnesium (hypomagnesemia), or low levels of calcium (hypocalcemia) Hypothyroidism (an underactive thyroid gland) |
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Musculoskeletal disorders |
Tight calf muscles Myopathies (disorders that affect muscle) Structural disorders, such as flat feet or genu recurvatum (a deformity of the knee joint that causes the knee to bend backward) |
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Nerve disorders |
Motor neuron disease (nerve disorders that affect voluntary muscles—those controlled by conscious effort) Peripheral neuropathies (damage to nerves outside the brain and spinal cord) Compression of a spinal nerve root |
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Water balance disorders |
Excessive sweating with inadequate replacement of salt or potassium Effects of dialysis—for example, if too much fluid is removed from the body or if fluid is removed too quickly |
Other conditions |
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Exercise and lifestyle |
Cramping during or soon after exercise Sitting for a long time |
Disorders that cause similar symptoms
Some disorders cause symptoms that resemble muscle cramps.
Dystonias are involuntary muscle contractions, but they usually last longer and occur more often than cramps. Also, they tend to affect other muscles and may affect many other muscles, including any limb muscles as well as those of the back, neck, and voice. In contrast, benign leg cramps and exercise-associated muscle cramping tend to affect the calf muscles.
Tetany is continuous or periodic spasms of muscles throughout the body. These spasms usually last much longer than muscle cramps and are more widespread. The muscles may also twitch.
Illusory muscle cramps occur in some people. These people feel as if they are having cramps but no muscle contraction occurs.
Hardening of the arteries in the legs (peripheral arterial disease) may cause calf pain (claudication) during physical activity such as walking. This pain is due to inadequate blood flow to muscles, not to muscle contraction as occurs with cramps.
Evaluation
The following information can help people decide whether a doctor's evaluation is needed and help them know what to expect during the evaluation.
Warning signs
In people with muscle cramps, the following symptoms and characteristics are of particular concern:
If people have cramps in the arms or trunk or muscle twitching, the cause is more likely to be a disorder (such as an electrolyte or hormonal disorder) or a drug than benign leg cramps or exercise-related muscle cramps.
When to see a doctor
People with muscle cramps should consult a doctor as soon as possible if they also have alcoholism, sudden weakness or loss of sensation, or severe symptoms or if they have lost body fluids (for example, through vomiting, diarrhea, or excessive sweating). Otherwise, people should call their doctor to discuss how soon the doctor needs to see them.
What the doctor does
Doctors first ask questions about the person's symptoms and medical history and then does a physical examination. What doctors find during the history and physical examination often suggests a cause and the tests that may need to be done.
Doctors ask the person to describe the cramps, including the following:
Doctors ask about symptoms that suggest clues to the cause:
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Lack of menstrual periods or menstrual irregularities—symptoms that suggest pregnancy-related leg cramps
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Vomiting, diarrhea, use of diuretics, excessive exercise, and sweating—symptoms that suggest loss of body fluids or electrolytes
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Difficulty tolerating cold, weight gain, and coarse, thick skin—symptoms that may indicate hypothyroidism
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Weakness, pain, or loss of sensation—symptoms that suggest a nerve disorder
The person is also asked about use of drugs and alcohol, recent dialysis treatment, and any association between past dialysis treatments and muscle cramps.
The physical examination focuses first on the nervous system (neurologic examination), including assessment of muscles and reflexes. Doctors also inspect the skin for signs of the following:
Testing
No tests are routinely done.
If cramping is widespread, particularly if reflexes are overactive, doctors measure levels of blood sugar and electrolytes (including calcium and magnesium) and do blood tests to check for kidney malfunction (which can cause levels of calcium and magnesium to be abnormal).
If the cramped muscles are also weak, electromyography may be done. For this test, a small needle is inserted into a muscle to record the electrical activity of the muscle when the muscle is at rest and when it is contracting.
If muscle weakness is widespread and doctors think that it is related to a problem with the nervous system, magnetic resonance imaging (MRI) of the brain and spinal cord is done.
Prevention
Preventing cramps is the best approach. The following measures can help:
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Not exercising immediately after eating
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Gently stretching the muscles before exercising or going to bed
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Drinking plenty of fluids (particularly sports beverages that contain potassium) after exercise
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Not consuming caffeine (for example, in coffee or chocolate)
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Not smoking
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Avoiding drugs that are stimulants, such as ephedrine or pseudoephedrine (a decongestant contained in many products that do not require a prescription but are available only behind the pharmacy counter)
Stretching makes muscles and tendons more flexible and less likely to contract involuntarily. The runner's (gastrocnemius) stretch is the best stretch for preventing calf cramps. A person stands with one leg forward and bent at the knee and the other leg behind with the knee straight—a lunge position. The hands can be placed on the wall for balance. Both heels remain on the floor. The knee of the front leg is bent further until a stretch is felt along the back of the other leg. The greater the distance between the two feet and the more the front knee is bent, the greater the stretch. The stretch is held for 30 seconds and repeated 4 or 5 times. Then the set of stretches is repeated on the other side.
Treatment
If a disorder that can cause muscle cramps is identified, it is treated.
If a cramp occurs, stretching the affected muscle often relieves the cramp. For example, for a calf cramp, the person could use a hand to pull the foot and toes upward or could do the runner's stretch. Massage may temporarily relieve some types of cramps.
Most of the drugs prescribed to prevent cramps from recurring (including calcium supplements, magnesium carbonate, and benzodiazepines such as diazepam) have not proved to be effective, and they can have side effects. Quinine is no longer recommended as treatment for muscle cramps because of its side effects, such as vomiting, vision problems, ringing in the ears, and headaches. Mexiletine (used to treat abnormal heart rhythms) sometimes helps but also has many side effects, such as nausea, vomiting, tremors (rhythmic shaking of a body part), and seizures.
