Muscle spasms and cramps

Definition

Muscle spasms and cramps are spontaneous, often painful muscle contractions.

Description

The rapid, uncontrolled muscle contraction, or spasm, happens unexpectedly, with either no stimulation or some trivially small one. The muscle contraction and pain last for several minutes and then slowly ease. Cramps may affect any muscle but are most common in the calves, feet, and hands. While painful, they are harmless and, in most cases, not related to any underlying disorder. Nonetheless, cramps and spasms can be manifestations of many neurological or muscular diseases.

The terms cramp and spasm can be somewhat vague, and they are sometimes used to include types of abnormal muscle activity other than sudden painful contraction. These include stiffness at rest, slow muscle relaxation, and spontaneous contractions of a muscle at rest (fasciculation). Fasciculation is a type of painless muscle spasm, marked by rapid, uncoordinated contraction of many small muscle fibers. A critical part of diagnosis is distinguishing these different meanings and allowing the patient to describe the problem as precisely as possible.

Demographics

The exact incidence of muscle cramps and spasms is not known. They are more likely to occur in older children and teenagers who are participating in organized, competitive sports and strenuous aerobic activities.

Causes and symptoms

Causes

Normal voluntary muscle contraction begins when electrical signals are sent from the brain through the spinal cord along nerve cells called motor neurons. These include both the upper motor neurons within the brain and the lower motor neurons within the spinal cord and leading out to the muscle. At the muscle, chemicals released by the motor neuron stimulate the internal release of calcium ions from stores within the muscle cell. These calcium ions then interact with muscle proteins within the cell, causing the proteins (actin and myosin) to slide past one another. This motion pulls their fixed ends closer, thereby shortening the cell and, ultimately, the muscle itself. Recapture of calcium and unlinking of actin and myosin allow the muscle fiber to relax.

Abnormal contraction may be caused by unusual activity at any stage in this process. Certain mechanisms within the brain and the rest of the central nervous system help regulate contraction. Interruption of these mechanisms can cause spasm. Motor neurons that are overly sensitive may fire below their normal thresholds. The muscle membrane itself may be overly sensitive, causing contraction without stimulation. Calcium ions may not be recaptured quickly enough, causing prolonged contraction.

Structural disorders such as flat feet, hyperextended knees (genu recurvatum), and hypermobility syndrome (joints that can move beyond the normal range of motion) may predispose a person to developing leg cramps. Prolonged sitting, inappropriate leg positioning during sedentary activity, or standing on concrete flooring for prolonged periods may be associated with an increased incidence of leg cramps.

Interruption of brain mechanisms and overly sensitive motor neurons may result from damage to the nerve pathways. Possible causes include stroke , multiple sclerosis, cerebral palsy , neurodegenerative diseases, trauma, spinal cord injury , and nervous system poisons such as strychnine, tetanus , and certain insecticides. Nerve damage may lead to a prolonged or permanent muscle shortening called contracture.

Changes in muscle responsiveness may be due to or associated with the following:

• Prolonged exercise : Curiously, relaxation of a muscle actually requires energy to be expended. The energy is used to recapture calcium and to unlink actin and myosin. Normally, sensations of pain and fatigue signal that it is time to rest. Ignoring or overriding those warning signals can lead to such severe energy depletion that the muscle cannot be relaxed, causing a cramp. The familiar advice about not swimming after a heavy meal, when blood flow is directed away from the muscles, is intended to avoid this type of cramp.
• Exercising or participating in activities in high or humid temperatures: Copious sweating during prolonged exercise can lead to heat cramps, a condition associated with brief, painful cramps, especially in the legs, sweating, and mild fever , usually less than 102°F. Heat cramps are more likely to occur when the child has not taken in enough fluids before, during, and after the activity. Exercising in high temperatures without adequate fluid intake may increase the risk of dehydration .
• Dehydration and salt depletion: This condition may be brought on by repeated bouts of vomiting or diarrhea or by copious sweating during prolonged exercise. Loss of fluids, salts, and minerals—especially sodium, potassium, magnesium, and calcium—can disrupt ion balances in both muscle and nerves. This imbalance can prevent the muscles and nerves from responding and recovering normally and can lead to cramping.
• Metabolic disorders that affect the energy supply in muscle: These are inherited diseases in which particular muscle enzymes are deficient. They include deficiencies of myophosphorylase (McArdle's disease), phosphorylase b kinase, phosphofructokinase, phosphoglycerate kinase, and lactate dehydrogenase.
• Myotonia: Myotonias include myotonic dystrophy , myotonia congenita, paramyotonia congenita, and neuromyotonia. These conditions cause stiffness due to delayed relaxation of the muscle but do not cause the spontaneous contraction usually associated with cramps. However, many patients with myotonia do experience cramping from exercise. Symptoms of myotonia are often worse in cold temperatures.

Fasciculation may be due to fatigue, cold, medications, metabolic disorders, nerve damage, or neurodegenerative disease, including amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig's disease). Most people experience brief, mild fasciculation from time to time, usually in the calves.

Symptoms

The pain of a muscle cramp is intense, localized, and often debilitating. Coming on quickly, it may last for minutes and fade gradually. Contractures develop more slowly, over days or weeks, and may be permanent if untreated. Fasciculation may occur at rest or after muscle contraction and may last several minutes.

Exercising in high temperatures can lead to dehydration. Dehydration should be suspected if these symptoms are present: dry mouth or tongue, increased or excessive thirst, few or no tears when crying, decreased urination, dark yellow urine, irritability, low energy, lightheadedness or fainting, severe weakness, and sunken abdomen, eyes and cheeks.

When to call the doctor

Prompt medical attention is required if the child has any of the symptoms associated with dehydration, as listed above. Prompt medical attention also is required if the child has a high fever— of 102°F or 38.9°C, or above. Parents also should call the child's pediatrician if the following symptoms are present:

• acute pain associated with the muscle cramp or spasm
• prolonged muscle contractions
• cramps or spasms that cause twisting and repetitive movement or abnormal posture
• apparent development of muscle contractures (prolonged joint flexion in an abnormal position)

Diagnosis

A usual bout of muscle cramps should not require a visit to the doctor. However, medical treatment is essential if the child has any symptoms of dehydration associated with the muscle cramps. In addition, any abnormal contractions or frequent muscle cramps or spasms that cause concern should be evaluated by a physician. Abnormal muscle contractions are diagnosed through a careful medical history, as well as a physical and neurological examination. In some cases when a structural abnormality is suspected, x rays may be performed.

The medical history helps the physician evaluate the presence of other conditions or disorders that might contribute to or cause the abnormal contractions. Records of previous diagnoses, surgeries, and treatments are reviewed. The child's family medical history is evaluated to determine if there is a history of muscular or neurological disorders.

Questions about the child's medical history may include:

• When were the symptoms first noticed?
• How long have the symptoms lasted?
• Are the symptoms always present?
• What muscles are affected?
• What makes the symptoms improve?
• What specific treatments or techniques have been tried?
• What makes the symptoms worse?
• Do certain activities, emotions, or events seem to aggravate the symptoms?
• Are other symptoms present?

The physical and neurological exams may include an evaluation of the child's motor reflexes including muscle tone, mobility, strength, balance, and endurance; heart and lung function; cranial nerve function; and an examination of the child's abdomen, spine, throat, and ears. The child's height and weight and blood pressure also are checked and recorded.

When a neurological cause is suspected, a multi-disciplinary team may be consulted to provide an accurate diagnosis, so the proper treatment can be planned. Occupational and physical therapy evaluations may be helpful to determine upper and lower extremity movement patterns and passive range of motion.

In some cases, nerve conduction studies with electromyography of the affected muscles may be performed to evaluate an underlying neuromuscular disorder. These tests are useful in evaluating a child's muscular activity and provide a comprehensive assessment of nerve and muscle function.

In both tests, the examiner uses a computer, monitor, amplifier, loudspeaker, stimulator, and high-tech filters to see and hear how the muscles and nerves are responding during the test. In the nerve conduction study, small electrodes are placed on the skin over the muscles to be examined. A stimulator delivers a very small electrical current (that does not cause damage to the body) through the electrodes, causing the nerves to fire. In the electromyogram, a very thin, sterilized needle is inserted into various muscles, usually those affected most by spasticity symptoms. The needle is attached by wires to a recording machine. The patient is asked to relax and contract the muscles being examined. The electrical signals produced by the nerves and muscles during these tests are measured and recorded by a computer and displayed as electrical waves on the monitor. The test results are interpreted by a specially trained physician.

Treatment

Most cases of simple cramps require no treatment other than patience and stretching. When heat cramps occur, the child should stop the activity, move to a cool or shady place, remove excess clothing, drink cool water or a sports drink with electrolytes, such as Gatorade, and rest. If the child appears nauseous or is feeling dizzy, he should lie down, with feet slightly elevated. Directing a fan on the child will help cool the child. Gently and gradually stretching and massaging the affected muscle may ease the pain and hasten recovery.

Briefly applying cold packs to cramped muscles, for about ten minutes, may help ease pain.

Acetaminophen (such as Tylenol) or ibuprofen (such as Advil or Motrin) should be used sparingly for relief of discomfort. Ask the child's doctor for specific guidelines. More prolonged or regular cramps may be treated with prescribed medications.

If the child has any signs of dehydration, generous amounts of fluids and an oral rehydrating solution containing glucose and electrolytes should be given. Oral rehydrating solutions, including brands such as Pedialyte, Infalyte, Ceralyte, and Oralyte, are available at most grocery stores and drug stores. They are essential for replacing fluids, minerals , and salts. Dehydration can upset the body's electrolyte balance, leading to potentially life-threatening problems such as heart beat abnormalities (arrhythmia). Prolonged, severe dehydration requires medical treatment with intravenous (IV) fluids and may require hospitalization .

Treatment of underlying metabolic or neurologic diseases, when possible, may help relieve symptoms.

KEY TERMS

Active motion —Spontaneous; produced by active efforts. Active range of motion exercises are those that are performed by the patient without assistance.

Acupuncture —Based on the same traditional Chinese medical foundation as acupressure, acupuncture uses sterile needles inserted at specific points to treat certain conditions or relieve pain.

Anoxia —Lack of oxygen.

Ataxia —A condition marked by impaired muscular coordination, most frequently resulting from disorders in the brain or spinal cord.

Biofeedback —A training technique that enables an individual to gain some element of control over involuntary or automatic body functions.

Central nervous system —Part of the nervous system consisting of the brain, cranial nerves, and spinal cord. The brain is the center of higher processes, such as thought and emotion and is responsible for the coordination and control of bodily activities and the interpretation of information from the senses. The cranial nerves and spinal cord link the brain to the peripheral nervous system, that is the nerves present in the rest of body.

Cerebral palsy —A nonprogressive movement disability caused by abnormal development of or damage to motor control centers of the brain.

Clonic —Referring to clonus, a series of muscle contractions and partial relaxations that alternate in some nervous diseases in the form of convulsive spasms.

Contraction —A tightening of the uterus during pregnancy. Contractions may or may not be painful and may or may not indicate labor.

Contracture —A tightening or shortening of muscles that prevents normal movement of the associated limb or other body part.

Dystonia —Painful involuntary muscle cramps or spasms.

Fasciculations —Small involuntary muscle contractions visible under the skin.

Genu recurvatum —Hyperextension of the knee.

Hyperactive reflexes —Reflexes that persist too long and may be too strong. For example, a hyperactive grasp reflex may cause the hand to stay clenched in a tight fist.

Hypermobility —Unusual flexibility of the joints, allowing them to be bent or moved beyond their normal range of motion.

Hypertonia —Having excessive muscular tone or strength.

Idiopathic —Refers to a disease or condition of unknown origin.

Motor neuron —A nerve cell that specifically controls and stimulates voluntary muscles.

Multiple sclerosis —A progressive, autoimmune disease of the central nervous system characterized by damage to the myelin sheath that covers nerves. The disease, which causes progressive paralysis, is marked by periods of exacerbation and remission.

Muscle spasm —Localized muscle contraction that occurs when the brain signals the muscle to contract.

Myoclonus —Involuntary contractions of a muscle or an interrelated group of muscles. Also known as myoclonic seizures.

Neurologist —A doctor who specializes in disorders of the nervous system, including the brain, spinal cord, and nerves.

Neurosurgeon —Physician who performs surgery on the nervous system.

Nocturnal leg cramps —Cramps that may be related to exertion and awaken a person during sleep.

Occupational therapist —A healthcare provider who specializes in adapting the physical environment to meet a patient's needs. An occupational therapist also assists patients and caregivers with activities of daily living and provide instructions on wheelchair use or other adaptive equipment.

Orthopedist —A doctor specializing in treatment of the musculoskeletal system.

Passive movement —Movement that occurs under the power of an outside source such as a clinician. There is no voluntary muscular contraction by the individual who is being passively moved.

Periodic limb movement disorder —A disorder characterized by involuntary flexion of leg muscles, causing twitching and leg extension or kicking during sleep.

Peripheral nerves —Nerves outside the brain and spinal cord that provide the link between the body and the central nervous system.

Physiatrist —A physician who specializes in physical medicine and rehabilitation.

Physical therapist —A healthcare provider who teaches patients how to perform therapeutic exercises to maintain maximum mobility and range of motion.

Range of motion (ROM) —The range of motion of a joint from full extension to full flexion (bending) measured in degrees like a circle.

Restless legs syndrome (RLS) —A disorder in which the patient experiences crawling, aching, or other disagreeable sensations in the calves that can be relieved by movement. RLS is a frequent cause of difficulty falling asleep at night.

Rigidity —A constant resistance to passive motion.

Spinal cord injury —Injury to the spinal cord, via blunt or penetrating trauma.

Stroke —Interruption of blood flow to a part of the brain with consequent brain damage. A stroke may be caused by a blood clot or by hemorrhage due to a burst blood vessel. Also known as a cerebrovascular accident.

Alternative treatment

Alternative and complementary therapies include approaches that are considered to be outside the mainstream of traditional health care. In adults, alternative treatments for cramps include gingko (Ginkgo biloba ) or Japanese quince (Chaenomeles speciosa ). Supplements of vitamin E, niacin, calcium, and magnesium may also help to relieve the likelihood of night cramps, especially when taken at bedtime. Indications for these treatments in children have not been documented.

There are several alternative therapies that can be useful when treating movement disorders . Among the therapies that may be helpful are acupuncture, homeopathy, touch therapies, postural alignment therapies, and biofeedback. The progress made will depend on the individual and his/her condition.

Biofeedback training may be used to teach older children how to consciously reduce muscle tension. Biofeedback uses an electrical signal that indicates when a spastic muscle relaxes. The patient may be able to use biofeedback to learn how to consciously reduce muscle tension and possibly reduce symptoms.

Before learning or practicing any particular technique, it is important for the parent or caregiver and child to learn about the therapy, its safety and effectiveness, potential side effects, and the expertise and qualifications of the practitioner. Although some practices are beneficial, others may be harmful to certain patients. Alternative therapies should not be used as a substitute for medical therapies prescribed by a doctor. Parents should discuss these alternative treatments with the child's doctor to determine the techniques and remedies that may be beneficial for the child.

Prognosis

Occasional cramps are common and have no special medical significance.

Prevention

The likelihood of developing cramps may be reduced with regular exercise to build up energy reserves in the muscles. Avoiding exercising in extreme heat helps prevent heat cramps. Heat cramps can also be avoided by drinking plenty of water before and during exercise in extreme heat. Practicing proper body mechanics while sitting (sitting with both feet on the floor, back straight and legs uncrossed) can help prevent the development of leg cramps. Taking a warm bath before bedtime may increase circulation to the legs and reduce the incidence of nighttime leg cramps.

Nutritional concerns

The likelihood of developing cramps may be reduced by eating a well-balanced, healthy diet with appropriate levels of minerals. A registered dietitian can work with parents to identify a child's specific calorie needs and develop an individualized meal plan.

Fluids should be encouraged during all strenuous activities, especially in warm weather. People should aim for two to four eight-ounce glasses of fluid per hour of activity.

If an underlying neurological disorder has been identified, dietary guidelines are individualized, based on the child's age, diagnosis, overall health, caloric and energy needs, and level of functioning. Early identification, treatment, and correction of specific feeding problems will improve the health and nutritional status of the patient.

Parental concerns

Occasional muscle cramps are common. The most important concern is preventing dehydration, especially when the child is exercising in high or humid temperatures. Make sure the child drinks enough fluids before, during, and after sports and other activities. Pack a water bottle and/or sports drink for the child to have at sports practices, games, and other physical activities. Make sure the coach provides time out for water breaks. After the activity, encourage the child to continue drinking water to replace lost fluids.

If a movement disorder has been diagnosed, parents should work closely with the child's therapists and doctors to create an effective treatment plan. It is important for parents to communicate their treatment goals with the health care team. Parents should take an active role in the child's exercise program.

Raising a child with a movement disorder can be challenging. There are several support groups available to provide information and assistance.

Resources

BOOKS

Bradley, Walter G., et al. Neurology in Clinical Practice,4th ed. Woburn, MA: Butterworth-Heinemann, 2003.

Martini, Frederic H. Fundamentals of Anatomy and Physiology, 6th ed. Englewood Cliffs, NJ: Prentice Hall, 2002.

ORGANIZATIONS

National Institute of Neurological Disorders and Stroke (NINDS). National Institutes of Health. PO Box 5801, Bethesda, MD 20824. Web site: <www.ninds.nih.gov/about_ninds>.

National Rehabilitation Information Center (NARIC). 4200 Forbes Blvd., Ste. 202, Lanham, MD 20700. Web site: <www.naric.com>.

Richard Robinson Angela M. Costello

Muscle Relaxants

Resources

Muscle relaxants are drugs that are administered to relieve the discomfort of muscle spasm or involuntary muscle contracture and also in cases of surgery to relax muscles and provide easier access for the surgeon. Some nonprescription drugs are available to combat painful contraction of the uterus during a woman’s menstrual period. The muscle relaxant cyclobenzaprine (Flexeril^®), for instance, is sometimes used to treat fibromyalgia, a condition that involves aches, stiffness, and fatigue.

Muscle relaxants work by acting on the central nervous system. In the United States, they are available only with a physician’s prescription. Examples of muscle relaxants are carisoprodol (Soma^®), chlorzoxazone (Parafon Forte DSC^®), cyclobenzaprine (Flexeril^®), and methocarbamol (Robaxin^®). Most come only in tablet form. However, methocarbamol (Robaxin^®) is available in both tablet and injectable forms. Some muscle relaxants are available in Canada without a prescription.

Muscles can be divided into two classes, the voluntary or skeletal muscles and the involuntary or smooth muscles. The heart muscle, the myocardium, is a unique type of muscle that does not fit into either category. Skeletal muscles are those that are under voluntary control. The muscles that move the arms, that move the legs when you walk or run, or those that are involved in chewing are all skeletal muscles. They come into play only when a person consciously tells them to work. Smooth muscles are those that are not under conscious control. The muscles in the digestive organs, for example, are smooth muscles.

Usually it is the skeletal or striated muscles that will require therapy for painful spasm or will need to be relaxed to allow the surgeon to gain access to the abdomen easily. Muscle spasm may be associated with a trauma or may be brought on by multiple sclerosis, cerebral palsy, stroke, or an injury to the spinal cord. Severe cold, an interruption of blood supply to a muscle, or overexertion of the muscle also can lead to spasms. A muscle spasm actually is an increase in muscle tone brought on by an abnormality in motor control by the spinal nerves.

Skeletal muscles are controlled by large nerves in the spinal cord. The nerve cell or neuron is part of the spinal cord, but its projections, the axon and the many dendrites course outward to connect to muscle cells. The nerve axon is a sensory device that senses the muscle cells’ current condition. The dendrites are motor fibers that deliver the instructions to change its state to the muscle fiber. The area at which the muscle and nerve connect is called the neuromuscular junction. It is here that the end releases a chemical called a neurotransmitter that crosses the microscopic space between the nerve and muscle and causes the desired response. Five such neurotransmitters have been described: acetylcholine, serotonin, norepinephrine, glycine, and gamma-amminobutyric acid or GABA. Of these, the functions of three are known. Acetylcholine excites muscle activity and glycine and GABA inhibit it.

Muscle relaxants may act either peripherally, that is directly on the muscle, or centrally, in the spinal cord. Most such drugs act centrally, though how they perform their task is not understood. These drugs do not act directly on the muscle to relax it, they do not interfere with conduction along the nerve fiber, they do not stop the neurotransmitter from being released or crossing the nerve-muscle junction, and they do not alter the ability of the muscle to respond to the neurotransmitter. Somehow they act centrally to depress the central nervous system and may have a sedative effect.

The dosage of any muscle relaxing agent must be carefully tailored to achieve the desired result without overdosing the patient. Because these drugs have a sedative action the patient should be warned not to drive, operate machinery or perform any other task that requires wakefulness. An overdose of the drugs can put the patient to sleep and may well depress muscle function to the extent that the bladder will not contract normally and urine retention will occur. Also, some drugs will produce a change in the color of the urine of which the patient should be made aware.

The centrally acting muscle relaxants have an onset of action ranging from 30 minutes to one hour. They reach their maximum concentration in the blood between one to eight hours, and their effects last for four to 24 hours. Dosages are designed to allow some

overlap to maintain the desired blood concentration of the drug for maximum benefit.

Only one drug is classified as a peripherally acting muscle relaxant. This agent, dantrolene sodium, acts directly on the muscle, so it has fewer side effects than do the centrally acting drugs. Dantrolene is marketed as Dantrium^® by its manufacturer. It is a slow-acting drug whose peak effect is not felt for some five hours after it has been taken. The peak effect of a single dose, however, does not constitute a therapeutic dose. The therapeutic effects of the drug may not be seen for up to a week or longer. The patient may be tempted to increase the dosage of the drug because it seems to have little effect in the beginning stages of therapy. Of course, this could be a critically unwise procedure that would be seen once the therapeutic dosage is built up.

Dantrolene seems to work directly on the muscle cell, affecting the sarcoplasmic reticulum within the cell. The sarcoplasmic reticulum in a muscle cell stores calcium. When the electrical signal through the nerve releases an excitatory neurotransmitter, the sarcoplasmic reticulum releases calcium, which brings on the contraction of the muscle. Dantrolene seems to prevent the release of calcium, and thus short-circuits the muscle contraction.

Baclofen (marketed as Llorosal^®) is another muscle relaxant that acts on the spinal cord to lessen muscle spasms especially in patients with multiple sclerosis or spinal cord injuries. The chemical structure of baclofen is similar to that of the neurotransmitter GABA, which is an inhibitory chemical. Baclofen seems to inhibit neuron activity, which reduces muscle tone and reduces spasm. Its primary usage is in patients with spinal cord injury that has resulted in paralysis. The drug relaxes tightly flexed leg muscles, improves bowel and bladder control, and reduces muscle spasms both in number and severity. Baclofen builds up slowly and may require a month or two of therapy before the optimal dose is achieved. It does not have a high degree of sedative effect, so it may be preferable for many patients.

Another drug used to treat muscle spasms, diazepam, commonly known by its trade name, Valium^®, is a tranquilizer or antianxiety and anticonvulsant drug. Still, it has found a niche as a muscle relaxing drug in cases of acute, painful muscle spasm. Diazepam appears to work by enhancing the effects of the inhibitory neurotransmitter GABA. Only small doses of diazepam can be given as a muscle relaxant because of its sedative effects. For the patient who is not sensitive to the sedation often brought about by diazepam, the drug can serve both to relieve muscle spasm and to relieve anxiety about that situation.

All muscle relaxing agents should be given with caution to anyone who is taking other drugs. The muscle relaxants will enhance the sedative effects of many other classes of drugs such as antihistamines, antidepressants, sedatives, other muscle relaxants, and tranquilizers.

Muscle relaxants are usually prescribed along with rest, exercise, physical therapy, or other treatments. Although the drugs may provide relief, they should never be considered a substitute for these other forms of treatment. These drugs may make the injury feel so much better that one is tempted to go back to

KEY TERMS

Neuromuscular junction —The point at which a nerve ending intersects with a muscle cell. The nerve controls muscle movements.

Neurotransmitter —A chemical that is released from nerve ends to achieve a physiologic response, whether muscle contraction, speech, reflex action, or whatever.

Skeletal muscle —Also called voluntary or striated muscle, it is a muscle under conscious control by the individual. Striated muscles flex or extend the leg or arm, curl the fingers, move the jaw during chewing, and so forth.

Spasm —The uncontrolled tightening of a muscle to the point that it may become painful. A so-called Charlie horse is such a spasm.

Spinal nerve —A nerve fiber that rises from the spinal cord instead of directly from the brain. Spinal nerves control muscle movement without conscious thought from an individual.

normal activity, but doing too much too soon can actually make the injury worse.

In addition, they should not be suddenly discontinued. Stopping the drugs suddenly can lead to a return of symptoms to an even more painful degree. After the optimal clinical dosage is reached the physician will provide the drugs until the muscle spasm has passed and then wean the patient off the drug. In some cases, as in paraplegia, the drug may be given for years to maintain the patient’s comfort.

People with certain medical conditions or who are taking certain other medicines can have problems if they take muscle relaxants. Diabetics should be aware that the metaxalone (Skelaxin^®) may cause false test results on one type of test for sugar in the urine. People with epilepsy should be cautioned that taking the muscle relaxant methocarbamol may increase the likelihood of seizures.

Anyone who has allergies, who is breastfeeding has kidney disease, has suffered a recent heart attack or irregular heartbeat, has an overactive thyroid gland, hepatitis or liver disease, is a current or former drug or alcohol abuser, has glaucoma, or has problems with urination should discuss their condition with their doctor before taking muscle relaxants.

See also Muscular system.

Resources

BOOKS

Griffith, H. Winter. Complete Guide to Prescription and Non-Prescription Drugs. New York: Penguin Group, 2005.

Levinthal, Charles F. Drugs, Behavior, and Modern Society. Boston, MA: Pearson/Allyn and Bacon, 2005.

Larry Blaser

Muscle relaxants

Muscle relaxants are drugs that are administered to relax muscles. They are given to relieve the discomfort of muscle spasm or involuntary muscle contracture and also in cases of surgery to relax muscles and provide easier access for the surgeon. Some nonprescription drugs are available to combat painful contraction of the uterus during a woman's menstrual period.

Muscles can be divided into two classes, the voluntary or skeletal muscles and the involuntary or smooth muscles. The heart muscle, the myocardium, is a unique type of muscle that does not fit into either category. Skeletal muscles are those that are under voluntary control. The muscles that move the arms, that move the legs when you walk or run, or those that are involved in chewing are all skeletal muscles. They come into play only when you will them. Smooth muscles are those that are not under conscious control. The muscles in the digestive organs are smooth muscles.

Usually it is the skeletal or striated muscles that will require therapy for painful spasm or will need to be relaxed to allow the surgeon to gain access to the abdomen easily. Muscle spasm may be associated with a trauma or may be brought on by multiple sclerosis, cerebral palsy, stroke , or an injury to the spinal cord. Severe cold, an interruption of blood supply to a muscle, or overexertion of the muscle also can lead to spasms. A muscle spasm actually is an increase in muscle tone brought on by an abnormality in motor control by the spinal nerves.

Skeletal muscles are controlled by large nerves in the spinal cord. The nerve cell or neuron is part of the spinal cord, but its projections, the axon and the many dendrites course outward to connect to muscle cells. The nerve axon is a sensory device that senses the muscle cells' current condition. The dendrites are motor fibers that deliver the instructions to change its state to the muscle fiber. The area at which the muscle and nerve connect is called the neuromuscular junction. It is here that the end releases a chemical called a neurotransmitter that crosses the microscopic space between the nerve and muscle and causes the desired response. Five such neurotransmitters have been described: acetylcholine , serotonin, norepinephrine, glycine, and gamma-amminobutyric acid or GABA. Of these, the functions of three are known. Acetylcholine excites muscle activity and glycine and GABA inhibit it.

Muscle relaxants may act either peripherally, that is directly on the muscle, or centrally, in the spinal cord. Most such drugs act centrally, though how they perform their task is not understood. These drugs do not act directly on the muscle to relax it, they do not interfere with conduction along the nerve fiber, they do not stop the neurotransmitter from being released or crossing the nerve-muscle junction, and they do not alter the ability of the muscle to respond to the neurotransmitter. Somehow they act centrally to depress the central nervous system and may have a sedative effect.

The dosage of any muscle relaxing agent must be carefully tailored to achieve the desired result without overdosing the patient. Because these drugs have a sedative action the patient should be warned not to drive, operate machinery or perform any other task that requires wakefulness. An overdose of the drugs can put the patient to sleep and may well depress muscle function to the extent that the bladder will not contract normally and urine retention will occur. Also, some drugs will produce a change in the color of the urine of which the patient should be made aware.

The centrally acting muscle relaxants have an onset of action ranging from 30 minutes to an hour. They reach their maximum concentration in the blood between 1-8

hours, and their effects last for 4-24 hours. Dosages are designed to allow some overlap to maintain the desired blood concentration of the drug for maximum benefit.

Only one drug is classified as a peripherally acting muscle relaxant. This agent, dantrolene sodium , acts directly on the muscle, so it has fewer side effects than do the centrally acting drugs. Dantrolene is marketed as Dantrium by its manufacturer. It is a slow-acting drug whose peak effect is not felt for some five hours after it has been taken. The peak effect of a single dose, however, does not constitute a therapeutic dose. The therapeutic effects of the drug may not be seen for up to a week or longer. The patient may be tempted to increase the dosage of the drug because it seems to have little effect in the beginning stages of therapy. Of course, this could be a critically unwise procedure that would be seen once the therapeutic dosage is built up.

Dantrolene seems to work directly on the muscle cell, affecting the sarcoplasmic reticulum within the cell. The sarcoplasmic reticulum in a muscle cell stores calcium . When the electrical signal through the nerve releases an excitatory neurotransmitter the sarcoplasmic reticulum releases calcium, which brings on the contraction of the muscle. Dantrolene seems to prevent the release of calcium, and thus short-circuits the muscle contraction.

Baclofen (marketed as Llorosal) is another muscle relaxant that acts on the spinal cord to lessen muscle spasms especially in patients with multiple sclerosis or spinal cord injuries. The chemical structure of baclofen is similar to that of the neurotransmitter GABA, which is an inhibitory chemical. Baclofen seems to inhibit neuron activity, which reduces muscle tone and reduces spasm. Its primary usage is in patients with spinal cord injury that has resulted in paralysis. The drug relaxes tightly flexed leg muscles, improves bowel and bladder control, and reduces muscle spasms both in number and severity. Baclofen builds up slowly and may require a month or two of therapy before the optimal dose is achieved. It does not have a high degree of sedative effect, so it may be preferable for many patients.

Another drug used to treat muscle spasms, diazepam, commonly known by its trade name, Valium, is a tranquilizer or antianxiety and anticonvulsant drug. Still, it has found a niche as a muscle relaxing drug in cases of acute, painful muscle spasm. Diazepam appears to work by enhancing the effects of the inhibitory neurotransmitter GABA. Only small doses of diazepam can be given as a muscle relaxant because of its sedative effects. For the patient who is not sensitive to the sedation often brought about by diazepam, the drug can serve both to relieve muscle spasm and to relieve anxiety about that situation.

All muscle relaxing agents should be given with caution to anyone who is taking other drugs. The muscle relaxers will enhance the sedative effects of many other classes of drugs such as antihistamines , antidepressants, sedatives, other muscle relaxants, and tranquilizers .

In addition, they should not be suddenly discontinued. Stopping the drugs suddenly can lead to a return of symptoms to an even more painful degree. After the optimal clinical dosage is reached the physician will provide the drugs until the muscle spasm has passed and then wean the patient off the drug. In some cases, as in paraplegia, the drug may be given for years to maintain the patient's comfort.

See also Muscular system.

Resources

books

Griffith, H. Winter. Complete Guide to Prescription and Non-Prescription Drugs. Los Angeles: The Body Press, 1991.

Larry Blaser

KEY TERMS

Neuromuscular junction

—The point at which a nerve ending intersects with a muscle cell. The nerve controls muscle movements.

Neurotransmitter

—A chemical that is released from nerve ends to achieve a physiologic response, whether muscle contraction, speech, reflex action, or whatever.

Skeletal muscle

—Also called voluntary or striated muscle, it is a muscle under conscious control by the individual. Striated muscles flex or extend the leg or arm, curl the fingers, move the jaw during chewing, and so forth.

Spasm

—The uncontrolled tightening of a muscle to the point that it may become painful. A socalled Charlie horse is such a spasm.

Spinal nerve

—A nerve fiber that rises from the spinal cord instead of directly from the brain. Spinal nerves control muscle movement without conscious thought from an individual.

Muscle Relaxants

Definition

Skeletal muscle relaxants are drugs that relax striated muscles (those that control the skeleton). They are a separate class of drugs from the muscle relaxant drugs used during intubations and surgery to reduce the need for anesthesia and facilitate intubation.

Purpose

Skeletal muscle relaxants may be used for relief of spasticity in neuromuscular diseases, such as multiple sclerosis, as well as for spinal cord injury and stroke. They may also be used for pain relief in minor strain injuries and control of the muscle symptoms of tetanus. Dantrolene (Dantrium) has been used to prevent or treat malignant hyperthermia in surgery.

Description

Although the muscle relaxants may be divided into only two groups, centrally acting and peripherally acting, the centrally acting group, which appears to act on the central nervous system, contains 10 drugs which are chemically different, while only dantrolene has a direct action at the level of the nerve-muscle connection.

Baclofen (Lioresal) may be administered orally or intrathecally for control of spasticity due to neuromuscular disease.

Carisoprodol (Soma), chlorphenesin (Maolate), chlorzoxazone (Paraflex), cyclobenzaprine (Flexeril), diazepam (Valium), metaxalone (Skelaxin), methocarbamol (Robaxin), and orphenadrine (Norflex) are used primarily as an adjunct for rest in management of acute muscle spasms associated with sprains. Muscle relaxation may also be an adjunct to physical therapy in rehabilitation following stroke, spinal cord injury, or other musculoskeletal conditions.

Diazepam and methocarbamol are also used by injection for relief of tetanus.

Recommended dosage

Dose varies with the drug, route of administration, and purpose. There may be individual variations in absorption that require doses higher than those usually recommended, particularly with methocarbamol. Consult specific references for further information.

Precautions

All drugs in this class may cause sedation. Baclofen, when administered intrathecally, may cause severe central nervous system (CNS) depression with cardiovascular collapse and respiratory failure.

Diazepam may be addictive. It is a controlled substance under federal law.

Dantrolene has a potential for hepatotoxicity. The incidence of symptomatic hepatitis is dose related, but may occur even with a short period of doses at or above. Even short periods of doses at or above 800 mg per day greatly increases the risk of serious liver injury. Overt hepatitis has been most frequently observed between the third and twelfth months of therapy. Risk of hepatic injury appears to be greater in women, in patients over 35 years of age and in patients taking other medications in addition to dantrolene.

Tizanidine may cause low blood pressure, but this may be controlled by starting with a low dose and increasing it gradually. The drug may rarely cause liver damage.

Methocarbamol and chlorzoxazone may cause harmless color changes in urine—orange or reddishpurple with chlorzoxazone and purple, brown, or green with methocarbamol. The urine will return to its normal color when the patient stops taking the medicine.

Most drugs in this class are well tolerated.

Not all drugs in this group have been evaluated for safety in pregnancy and breast feeding.

Baclofen is pregnancy category C. It has caused fetal abnormalities in rats at doses 13 times above the human dose. Baclofen passes into breast milk, and breast feeding while taking baclofen is not recommended.

Diazepam is category D. All benzodiazepines cross the placenta. Although the drugs appear to be safe for use during the first trimester of pregnancy, use later in pregnancy may be associated with cleft lip and palate. Diazepam should not be taken while breast feeding. Infants who were breast fed while their mothers took diazepam were excessively sleepy and lethargic.

Dantrolene is category C. In animal studies it has reduced the rate of survival of the newborn when given in doses seven times the normal human dose. Mothers should not breast feed while receiving dantrolene.

Interactions

Skeletal muscle relaxants have many potential drug interactions. Individual references should be consulted.

Because these drugs cause sedation, they should be used with caution with other drugs that may also cause drowsiness.

The activity of diazepam may be increased by drugs that inhibit its metabolism in the liver. These include: Cimetidine, oral contraceptives, Disulfiram, Fluoxetine, Isoniazid, Ketoconazole, Metoprolol, Propoxyphene, Propranolol, and Valproic acid.

Dantrolene may have an interaction with estrogens. Although no interaction has been demonstrated, the rate of liver damage in women over the age of 35 who were taking estrogens is higher than in other groups.

KEY TERMS

Central nervous system— The brain and spinal cord.

Intrathecal— Introduced into or occurring in the space under the arachnoid membrane which covers the brain and spinal cord.

Pregnancy category— A system of classifying drugs according to their established risks for use during pregnancy. Category A: Controlled human studies have demonstrated no fetal risk. Category B: Animal studies indicate no fetal risk, but no human studies, or adverse effects in animals, but not in well-controlled human studies. Category C: No adequate human or animal studies, or adverse fetal effects in animal studies, but no available human data. Category D: Evidence of fetal risk, but benefits outweigh risks. Category X: Evidence of fetal risk. Risks outweigh any benefits.

Sedative— Medicine used to treat nervousness or restlessness.

Spasm— Sudden, involuntary tensing of a muscle or a group of muscles.

Tranquilizer (minor)— A drug that has a calming effect and is used to treat anxiety and emotional tension.

Muscle Spasms and Cramps

Definition

Muscle spasms and cramps are spontaneous, often painful muscle contractions.

Description

Most people are familiar with the sudden pain of a muscle cramp. The rapid, uncontrolled contraction, or spasm, happens unexpectedly, with either no stimulation or some trivially small one. The muscle contraction and pain last for several minutes, and then slowly ease. Cramps may affect any muscle, but are most common in the calves, feet, and hands. While painful, they are harmless, and in most cases, not related to any underlying disorder. Nonetheless, cramps and spasms can be manifestations of many neurological or muscular diseases.

The terms cramp and spasm can be somewhat vague, and they are sometimes used to include types of abnormal muscle activity other than sudden painful contraction. These include stiffness at rest, slow muscle relaxation, and spontaneous contractions of a muscle at rest (fasciculation). Fasciculation is a type of painless muscle spasm, marked by rapid, uncoordinated contraction of many small muscle fibers. A critical part of diagnosis is to distinguish these different meanings and to allow the patient to describe the problem as precisely as possible.

Causes and symptoms

Causes

Normal voluntary muscle contraction begins when electrical signals are sent from the brain through the spinal cord along nerve cells called motor neurons. These include both the upper motor neurons within the brain and the lower motor neurons within the spinal cord and leading out to the muscle. At the muscle, chemicals released by the motor neuron stimulate the internal release of calcium ions from stores within the muscle cell. These calcium ions then interact with muscle proteins within the cell, causing the proteins (actin and myosin) to slide past one another. This motion pulls their fixed ends closer, thereby shortening the cell and, ultimately, the muscle itself. Recapture of calcium and unlinking of actin and myosin allows the muscle fiber to relax.

Abnormal contraction may be caused by abnormal activity at any stage in this process. Certain mechanisms within the brain and the rest of the central nervous system help regulate contraction. Interruption of these mechanisms can cause spasm. Motor neurons that are overly sensitive may fire below their normal thresholds. The muscle membrane itself may be over sensitive, causing contraction without stimulation. Calcium ions may not be recaptured quickly enough, causing prolonged contraction.

Interuption of brain mechanisms and overly sensitive motor neurons may result from damage to the nerve pathways. Possible causes include stroke, multiple sclerosis, cerebral palsy, neurodegenerative diseases, trauma, spinal cord injury, and nervous system poisons such as strychnine, tetanus, and certain insecticides. Nerve damage may lead to a prolonged or permanent muscle shortening called contracture.

Changes in muscle responsiveness may be due to or associated with:

• Prolonged exercise. Curiously, relaxation of a muscle actually requires energy to be expended. The energy is used to recapture calcium and to unlink actin and myosin. Normally, sensations of pain and fatigue signal that it is time to rest. Ignoring or overriding those warning signals can lead to such severe energy depletion that the muscle cannot be relaxed, causing a cramp. The familiar advice about not swimming after a heavy meal, when blood flow is directed away from the muscles, is intended to avoid this type of cramp. Rigor mortis, the stiffness of a corpse within the first 24 hours after death, is also due to this phenomenon.
• Dehydration and salt depletion. This may be brought on by protracted vomiting or diarrhea, or by copious sweating during prolonged exercise, especially in high temperatures. Loss of fluids and salts—especially sodium, potassium, magnesium, and calcium—can disrupt ion balances in both muscle and nerves. This can prevent them from responding and recovering normally, and can lead to cramp.
• Metabolic disorders that affect the energy supply in muscle. These are inherited diseases in which particular muscle enzymes are deficient. They include deficiencies of myophosphorylase (McArdle's disease), phosphorylase b kinase, phosphofructokinase, phosphoglycerate kinase, and lactate dehydrogenase.
• Myotonia. This causes stiffness due to delayed relaxation of the muscle, but does not cause the spontaneous contraction usually associated with cramps. However, many patients with myotonia do experience cramping from exercise. Symptoms of myotonia are often worse in the cold. Myotonias include myotonic dystrophy, myotonia congenita, paramyotonia congenita, and neuromyotonia.

Fasciculations may be due to fatigue, cold, medications, metabolic disorders, nerve damage, or neurodegenerative disease, including amyotrophic lateral sclerosis. Most people experience brief, mild fasciculations from time to time, usually in the calves.

Symptoms

The pain of a muscle cramp is intense, localized, and often debilitating Coming on quickly, it may last for minutes and fade gradually. Contractures develop more slowly, over days or weeks, and may be permanent if untreated. Fasciculations may occur at rest or after muscle contraction, and may last several minutes.

Diagnosis

Abnormal contractions are diagnosed through a careful medical history, physical and neurological examination, and electromyography of the affected muscles. Electromyography records electrical activity in the muscle during rest and movement.

Treatment

Most cases of simple cramps require no treatment other than patience and stretching. Gently and gradually stretching and massaging the affected muscle may ease the pain and hasten recovery.

More prolonged or regular cramps may be treated with drugs such as carbamazepine, phenytoin, or quinine. Fluid and salt replacement, either orally or intravenously, is used to treat dehydration. Treatment of underlying metabolic or neurologic disease, where possible, may help relieve symptoms.

Alternative treatment

Cramps may be treated or prevented with Gingko (Ginkgo biloba ) or Japanese quince (Chaenomeles speciosa ). Supplements of vitamin E, niacin, calcium, and magnesium may also help. Taken at bedtime, they may help to reduce the likelihood of night cramps.

Prognosis

Occasional cramps are common, and have no special medical significance.

Prevention

The likelihood of developing cramps may be reduced by eating a healthy diet with appropriate levels of minerals, and getting regular exercise to build up energy reserves in muscle. Avoiding exercising in extreme heat helps prevent heat cramps. Heat cramps can also be avoided by taking salt tablets and water before prolonged exercise in extreme heat. Taking a warm bath before bedtime may increase circulation to the legs and reduce the incidence of nighttime leg cramps.

Resources

BOOKS

Bradley, Walter G., et al. Neurology in Clinical Practice. 2nd ed. Woburn, MA: Butterworth-Heinemann, 1995.

KEY TERMS

Motor neuron— Nerve cells within the central nervous system that carry nerve impulses controlling muscle movement.