CHAPTER 121
Muscle Cramps
(Charley Horse)
Presentation
The patient complains of painful, visible, palpable muscle contractions, often affecting the gastrocnemius muscle or small muscles of the foot or hand. Ordinary cramps occur chiefly at rest during the night or after trivial movement but also can occur after forceful muscle contraction. Other muscle cramps are associated with exercise in the heat, occupations that cause overuse, pregnancy, and drug or alcohol use. Most cramps are transient in nature, but they are likely to recur after a severe episode. Following this, the muscles may be tender and painful for some time.
What To Do:
Look for a specific underlying cause. Unaccustomed exercise and salt depletion from sweating are common precipitating causes (see Chapter 2). Drug-induced cramps can include those from alcohol, lithium, cimetidine, nifedipine, antipsychotic medications (see Chapter 1), clofibrate, and others. Hypothyroidism, hyperthyroidism, hyponatremia, hypokalemia, hyperkalemia, hypocalcemia, hypomagnesemia, and respiratory alkalosis (see Chapter 3) can all cause muscle cramping.
Address any specific cause. IV fluids with electrolyte replacement will help with heat cramps and alcohol-induced cramps.
Ordinary muscle cramps can be treated immediately with passive or active stretching of the cramped muscle (dorsiflexing the foot for calf cramps).
Nocturnal leg cramps have historically been treated with quinine sulfate tablets, 260 to 325 mg taken qhs. Most studies show that quinine and its derivatives decrease the incidence, severity, and duration of night cramps. However, not all report favorable results, and their use has become somewhat controversial. Recently, the Food and Drug Administration (FDA) has warned against using quinine for non–FDA-approved symptoms of leg cramps and restless leg syndrome, because of reports of hematologic reactions. A glass of tonic water (a source of quinine) before bed is a less toxic alternative worth trying.
Oral magnesium (Slo-Mag, Mag 64), qd or bid, can be used to reduce leg cramps in pregnant women, without increasing serum concentrations. Although one study failed to find a difference between magnesium and placebo in patients with nocturnal leg cramps, magnesium salts are commonly used to relieve nocturnal leg pain in Europe and Latin America.
Provide appropriate follow-up to patients who have more than benign self-limited cramps.
What Not To Do:
Do not ignore muscle weakness, fasciculations, and wasting, which are signs of lower motor neuron disorders, including amyotrophic lateral sclerosis, polyneuropathy, peripheral nerve injury, and nerve root compression. Fasciculation and cramps without weakness or muscle atrophy are recognized as a benign syndrome. If there is any uncertainty, a normal electromyogram will rule out any serious disease processes.
Discussion
Most muscle cramps are thought to be caused by hyperactivity of the peripheral or central nervous system rather than the muscle itself. The pain results from a combination of ischemia, accumulation of metabolites, and possible damage to the muscle fibers. Electromyographic studies indicate that during ordinary muscle cramps, motor units fire at about 300 per second, far more rapidly than any voluntary contraction. This rapid firing rate causes the muscle tightness and pain.
The cramps occur when a muscle already in its most shortened natural position contracts further. True cramps, which by definition occur in the absence of fluid or electrolyte imbalance, are more prevalent in patients with well-developed muscles, in the latter stages of pregnancy, and in patients with cirrhosis. They are typically asymmetric, explosive in onset, and most frequently affect the gastrocnemius muscle and small muscles of the foot. The contraction, which is often visible, may leave soreness and even swelling. The most common type of true muscle cramp occurs at rest, usually during the night. A small study showed that in elderly patients with nocturnal leg cramps that are unresponsive to quinine sulfate, verapamil provided relief to most. There are reports that nitroglycerin paste applied to the overlying skin may relieve a muscle cramp rapidly, but the dose must be small to avoid hypotension, headache, and flushing.
Muscle cramps can also be a considerable source of discomfort in patients undergoing hemodialysis. There is limited evidence that nifedipine can also provide significant pain relief to this group of patients. In another study of hemodialysis muscle cramps, the combination of vitamin C and E supplements produced a 97% decrease in cramps.
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