A muscle cramp (charley horse) is a sudden, brief, involuntary, painful contraction of a muscle or group of muscles. Cramps commonly occur in healthy people (usually middle-aged and elderly people), sometimes during rest, but particularly during or after exercise or at night (including during sleep—see Sleep and Wakefulness Disorders: Sleep-related leg cramps). Leg cramps at night usually occur in the calf and cause plantar flexion of the foot and toes.

Other disorders can simulate cramps:

• Dystonias can cause muscle spasm, but symptoms are usually more sustained and recurrent and involve muscles other than typical leg cramps (eg, neck, hand, face, muscles throughout the body).
• Tetany can cause muscle spasm, but spasm is usually more sustained (often with repetitive brief muscle twitches); it is usually bilateral and diffuse, but isolated carpopedal spasm may occur.
• Muscle ischemia during exertion in patients with peripheral arterial disease (claudication) may cause calf pain, but this pain is due to inadequate blood flow to muscles, and the muscles do not contract as with a cramp.
• Illusory cramps are the sensation of cramps in the absence of muscle contraction or ischemia.

Causes

The most common types of leg cramps are

• Benign idiopathic leg cramps (leg cramps in the absence of a causative disorder, typically at night)
• Exercise-associated muscle cramping (cramps during or immediately after exercise)

Although almost everyone has muscle cramps at some time, certain factors increase the risk and severity of cramps. They include dehydration, electrolyte abnormalities (eg, low body levels of potassium or magnesium), neurologic or metabolic disorders, and drugs. Tight calf muscles (eg, due to lack of stretching, inactivity, or sometimes chronic lower leg edema) commonly contribute to leg cramps.

Table 4
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Some Drugs and Disorders Associated With Muscle Cramps Cause Suggestive Findings Diagnosis Confirmed by Drugs Contributory drugs: ARBs, cisplatin, clofibrate, diuretics, donepezil, drugs with β-adrenergic agonist effects (including bronchodilators and some β-blockers), lovastatin, oral contraceptives, pyrazinamide, raloxifene, stimulants (eg, amphetamines, caffeine, cocaine, ephedrine, nicotine, pseudoephedrine), teriparatide, tolcapone, vincristine Withdrawal syndromes: Alcohol, barbiturates, benzodiazepines, sedative-hypnotics In patients taking a causative drug Clinical evaluation, including sometimes trial of withdrawal of suspected drug Disorders Extracellular fluid volume depletion and/or electrolyte abnormalities (eg, ionized hypocalcemia, low body potassium or magnesium) Sometimes excessive sweating, vomiting, diarrhea, use of a diuretic, signs of dehydration Sometimes occurring during or after hemodialysis or during late pregnancy (probably related to low body magnesium) Sometimes serum K, Mg, and/or ionized Ca Metabolic disorders (eg, alcoholism, hypothyroidism) Alcoholism: History of overuse; sometimes ascites, gynecomastia, spider angiomas, testicular atrophy Hypothyroidism: Cold intolerance, constipation, fatigue, sluggish reflexes Alcoholism: Clinical evaluation Hypothyroidism: Thyroid function testing Peripheral neuropathies Plexopathies Radiculopathies Motor neuron disease Weakness, sensory loss, pain, and/or hyporeflexia in a peripheral nerve, plexus, or nerve root distribution Fasciculations In motor neuron disease, weakness that begins in one hand or foot Clinical evaluation Sometimes EMG, nerve conduction studies, and/or spinal cord MRI Musculoskeletal abnormalities Tight calf muscles, a history of prolonged sitting In patients with structural disorders (eg, flat feet, genu recurvatum) Clinical evaluation Exercise-associated muscle cramping Cramping of involved muscles during exercise or in the few hours after exercise Clinical evaluation Benign idiopathic leg cramps Unprovoked and unexplained cramps, typically in calf muscles and at night Usually tight calf muscles Clinical evaluation ARBs = angiotensin II receptor blockers; EMG = electromyography.

Evaluation

Evaluation focuses on recognition of what is treatable. In many cases, a disorder contributing to cramps has already been diagnosed or causes other symptoms that are more troublesome than cramps.

History: History of present illness should elicit a description of cramps, including their duration, frequency, location, apparent triggers, and any associated symptoms. Symptoms that may be related to neurologic or muscle disorders can include muscle stiffness, weakness, pain, and loss of sensation. Factors that can contribute to dehydration or electrolyte or body fluid imbalances (eg, vomiting, diarrhea, excessive exercise and sweating, recent dialysis, diuretic use, pregnancy) are recorded.

Review of systems should seek symptoms of possible causes, including amenorrhea or menstrual irregularity (pregnancy-related leg cramps), cold intolerance with weight gain and skin changes (hypothyroidism), weakness (neurologic disorders), and pain or loss of sensation (peripheral neuropathies or radiculopathies).

Past medical history should include any disorders that can cause cramps. A complete drug history, including use of alcohol, is taken.

Physical examination: General examination should include the skin, looking for stigmata of alcoholism, nonpitting edema or loss of eyebrow hair (suggesting hypothyroidism), and changes in skin moisture or turgor. A neurologic examination, including deep tendon reflexes, is done. Pulses should be palpated, and BP measured in all extremities. A weak pulse or low ankle:brachial BP ratio in an affected limb may indicate ischemia.

Red flags: The following findings are of particular concern:

• Upper extremity or truncal involvement
• Hyperreflexia
• Muscle weakness
• Fasciculations
• Alcoholism
• Hypovolemia
• Pain or loss of sensation in a peripheral nerve, plexus, or root distribution

Interpretation of findings: Focal cramps suggest benign idiopathic leg cramps, exercise-associated muscle cramping, musculoskeletal abnormalities, peripheral nervous system causes, or an early degenerative disorder that can be asymmetric, such as a motor neuron disorder. Focal hyporeflexia suggests a peripheral neuropathy, plexopathy, or radiculopathy.

In patients with diffuse cramps (particularly those who are tremulous), hyperreflexia suggests a systemic cause (eg, ionized hypocalcemia; sometimes alcoholism, a motor neuron disorder, or a drug), although effects on deep tendon reflexes can vary by drug. Generalized hyporeflexia can suggest hypothyroidism and sometimes alcoholism or be a normal finding, particularly in the elderly.

A normal examination and compatible history suggests benign idiopathic leg cramps or exercise-associated muscle cramping.

Testing: Testing is done as indicated by abnormal clinical findings. No tests are routinely done.

Blood glucose, renal function tests, and electrolyte levels, including Ca and Mg, should be measured if patients have diffuse cramps of unknown cause, particularly if hyperreflexia is present. Ionized Ca and ABGs (to confirm respiratory alkalosis) are measured if patients have tetany. Electromyography is done if cramped muscles are weak. MRI of the brain and often spinal cord is done if muscle weakness is diffuse.

Treatment

• Stretching

Underlying conditions are treated when identified.

If a cramp occurs, stretching the affected muscles often relieves the cramp. For example, to relieve a calf cramp, patients can use their hand to pull the toes and foot upward (dorsiflexion).

Prevention

Measures to prevent cramps include the following:

• Not exercising immediately after eating
• Gently stretching the muscles before exercising or going to bed
• Drinking plenty of fluids (particularly beverages that contain potassium) after exercise
• Not consuming stimulants (eg, caffeine, nicotine, ephedrine, pseudoephedrine)

The runner's stretch is most useful. A person stands with one leg forward and bent at the knee and the other leg behind and 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 sec and repeated 5 times. The set of stretches is repeated on the other side.

Most of the drugs often prescribed to prevent cramps (eg, Ca supplements, quinine, magnesium, benzodiazepines) are not recommended. Most have no demonstrated efficacy. Quinine has been effective is some trials but is usually not recommended because of occasional serious side effects (eg, arrhythmias, thrombocytopenia, thrombotic thrombocytopenic purpura [TTP] and hemolytic-uremic syndrome [HUS], severe allergic reactions). Mexiletine sometimes helps, but whether using it is worth the risk of adverse effects is unclear. These effects include nausea, vomiting, heartburn, dizziness, and tremor.

Key Points

• Leg cramps are common.
• The most common causes are benign idiopathic leg cramps and exercise-associated muscle cramping.
• Cramps must be differentiated from claudication and dystonias; clinical evaluation is usually adequate.
• Stretching can help relieve and prevent cramps.
• Drug therapy is usually not recommended.

Last full review/revision August 2012 by Michael C. Levin, MD