Muscle Spasm
Muscle spasm or cramp is a sudden, involuntary, painful musle contraction that occurs with trauma or an irritant. Spasms may involve alternating contraction and relaxation (clonic) or sustained contraction (tonic). Muscle spasm may occur with musculoskeletal trauma or inflammation (eg, sprains, strains,
bursitis, arthritis). It is also encountered with acute or chronic low back pain, a common condition that is primarily a disorder of posture.
Spasticity
Spasticity involves increased muscle tone or contraction and stiff, awkward movements. It occurs with neurologic disorders such as spinal cord injury and multiple sclerosis.
In patients with spinal cord injury, spasticity requires treatment when it impairs safety, mobility, and the ability to perform activities of daily living (eg, self-care in hygiene, eating,dressing, and work or recreational activities). Stimuli that precipitate spasms vary from one individual to another and may
include muscle stretching, bladder infections or stones, constipation and bowel distention, or infections. Each person needs to be assessed for personal precipitating factors, so they
can be avoided when possible. Treatment measures include passive range-of-motion and muscle-stretching exercises and antispasmodic medications (eg, baclofen, dantrolene).
Multiple sclerosis (MS) is a major cause of neurologic disability among young and middle-aged adults, occurs
more often in women than in men, and has a pattern of exacerbations and remissions. It is considered an autoimmune disorder that occurs in genetically susceptible individuals,
although its cause is unknown. It involves destruction of portions of the myelin sheath that covers nerves in the brain, spinal cord, and optic nerve. Myelin normally insulates the
neuron from electrical activity and conducts electrical impulses rapidly along nerve fibers. When myelin is destroyed (a process called demyelination, which probably results from inflammation), fibrotic lesions are formed and nerve conduction is slowed or blocked around the lesions. Lesions
in various states of development (eg, acute, subacute, and chronic) often occur at multiple sites in the CNS. Muscle weakness and other symptoms vary according to the location and duration of the myelin damage.
In recent years, researchers have discovered that nerve cells can be repaired (remyelinated) if the process that damaged the myelin is stopped before the oligodendrocytes (the cells that form myelin) are destroyed. Other researchers are trying to develop methods for enhancing nerve conduction velocity in demyelinated nerves. For example, exposure to cold by wearing a cooling vest or exercising in cool water
temporarily increases the rate of nerve conduction and improves symptoms in some people. Avoiding environmental heat and conditions that cause fever may also help because an elevated body temperature slows nerve conduction and often aggravates MS symptoms.
The person with minimal symptoms does not require treatment, but should be encouraged to maintain a healthy lifestyle.
Those with more extensive symptoms should try to avoid emotional stress, environmental temperature extremes, infections, and excessive fatigue. Physical therapy may help main-
tain muscle tone, and occupational therapy may help maintainability to perform activities of daily living.
Drug therapy for MS may involve several types of medications for different types and stages of the disease. Acute exacerbations are treated with corticosteroids interferon beta (Avonex, Betaseron) or glatiramer (Copax-one) is given to prevent relapses, immunosuppressive drugs
(eg, methotrexate) are used to treat progressive disease, and symptoms are treated with a variety of drugs, including anti-depressants for depression and skeletal muscle relaxants for
spasticity.
Spasticity may be controlled with the use of baclofen, tizanidine, or dantrolene. In some cases, decreasing spasticity may not be desirable because clients with severe leg weakness
may require some degree of spasticity to ambulate. In cases of severe spasticity, baclofen may be given intrathecally through an implanted subcutaneous pump.
Mechanism of Action
All skeletal muscle relaxants except dantrolene are centrally active drugs. Pharmacologic action is usually attributed to general depression of the central nervous system (CNS), but may involve blockage of nerve impulses that cause increased muscle tone and contraction. It is unclear whether relief of
pain results from sedative effects, muscular relaxation, or a placebo effect. In addition, although parenteral administration of some drugs (eg, diazepam, methocarbamol) relieves
pain associated with acute musculoskeletal trauma or inflammation, it is uncertain whether oral administration of usual doses exerts a beneficial effect in acute or chronic dis-
orders.
Baclofen and diazepam increase the effects of gammaaminobutyric acid, an inhibitory neurotransmitter, and tizanidine inhibits motor neurons in the brain. Dantrolene is the only
skeletal muscle relaxant that acts peripherally on the muscle it self. It inhibits the release of calcium in skeletal muscle cells and thereby decreases the strength of muscle contraction.
Indications for Use
Skeletal muscle relaxants are used primarily as adjuncts to other treatment measures such as physical therapy. Occasionally, parenteral agents are given to facilitate orthopedic
procedures and examinations. In spastic disorders, skeletal muscle relaxants are indicated when spasticity causes severe pain or inability to tolerate physical therapy, sit in awheelchair, or participate in self-care activities of daily living (eg, eating, dressing). The drugs should not be given if
they cause excessive muscle weakness and impair rather than facilitate mobility and function.
Dantrolene also is indicated for prevention and treatment of malignant hyperthermia, a rare but life-threatening com plication of anesthesia characterized by hypercarbia, metabolic acidosis, skeletal muscle rigidity, fever, and cyanosis. For preoperative prophylaxis in people with previous
episodes of malignant hyperthermia, the drug is given orally for 1 to 2 days before surgery. For intraoperative malignant hyperthermia, the drug is given intravenously. After an occurrence during surgery, the drug is given orally for 1–3 days to prevent recurrence of symptoms.
Contraindications to Use
Most skeletal muscle relaxants cause CNS depression and have the same contraindications as other CNS depressants. They should be used cautiously in clients with impaired renal or
hepatic function or respiratory depression, and in clients who must be alert for activities of daily living (eg, driving a car, operating potentially hazardous machinery). Orphenadrine and
cyclobenzaprine have high levels of anticholinergic activity and therefore should be used cautiously with glaucoma, urinary retention, cardiac arrhythmias, or tachycardia.
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