Chronic Pain

Overview

Pain is an unpleasant sensation triggered by the nervous system. The ability to experience pain is critical for survival because it can make us immediately aware of injury to the body.Pain is an individual experience affected by environmental, emotional, and cognitive factors.

Pain can be a symptom of illness, result from an injury, or occur with no apparent cause. Pain that results from illness or injury and tapers off or stops on its own or with medical treatment is called acute pain. Pain that persists after healing has occurred, results from long-term illness, or has no apparent cause is called chronic pain.

Chronic pain may persist for weeks, months, or years and may not respond to treatment. It can be debilitating and often becomes the defining factor in patients' lives. Without relief, or the hope for relief, many patients lose the ability to eat, sleep, work, and function normally.

Chronic pain can cause patients to alienate those around them and often leads to drug addiction, irritability, and depression. Physical, psychological, and emotional stress may worsen chronic pain.

Incidence and Prevalence

According to the Centers for Disease Control and Prevention, chronic pain is the leading cause of disability in the United States. Chronic pain occurs in as many as 90% of cancer patients and often is undertreated.

Causes

Long-term illness or disease, ongoing conditions, and injuries are the most common causes for chronic pain. Other causes include damage to the central or peripheral nervous system and vascular conditions.

Long-term illnesses that may result in chronic pain include the following:

• Cancer
• Degenerative disease (e.g., osteoarthritis, osteoporosis)
• Fibromyalgia
• Inflammatory disease (e.g., rheumatoid arthritis)
• Multiple sclerosis

Cancer patients often experience chronic pain caused by tumors that infiltrate and compress organs or bones and by treatment (e.g., radiation, chemotherapy) that causes edema (tissue swelling).

Ongoing conditions that may cause chronic pain include ear infections, migraine headaches, and peripheral neuropathy (e.g., carpal tunnel syndrome).

Initial injuries (e.g., sprain, muscle strain) and under- and overuse injuries (e.g., back pain, Achilles tendonitis, and heel pain) also may become chronic.

Chronic pain caused by damage to the central nervous system (i.e., brain, brainstem, or spinal cord) or peripheral nervous system is called neurogenic pain. Central pain syndrome, trigeminal neuralgia, and phantom pain are types of neurogenic pain.

Central pain syndrome is a neurological condition caused by damage to the central nervous system. It may occur in patients who have experienced spinal cord injury, brain injury, or stroke and in patients with multiple sclerosis (MS). It is characterized by steady pain (usually described as a burning, aching, or cutting sensation) and brief bursts of sharp pain. Central pain syndrome may develop years after damage to the central nervous system occurs.

Trigeminal neuralgia, also called tic douloureux, is a condition caused by damage to the fifth cranial nerve (called the trigeminal nerve). This condition is characterized by severe, stabbing pain on one side of the jaw or cheek, typically lasting a few seconds and recurring throughout the day. Talking, brushing the teeth, touching the face, chewing, or swallowing may trigger an attack. Trigeminal neuralgia may persist for days or months, disappear, and recur months or years later.

Phantom pain or "ghost" pain is a type of neurogenic pain that occurs in paralyzed patients or as a result of limb amputation.

Chronic pain also may be caused by vascular conditions that reduce blood flow to an area of the body. Vascular headache is one of the most common types of headache.

Chronic pain that is not related to physical disease or injury, or other physical cause is called psychogenic pain. This type of pain is also referred to as pain disorder with psychological factors. Mental and emotional disorders may cause, increase, or prolong pain. Headache, muscle pain, back pain, and stomach pain are the most common types of psychogenic pain. Physicians and mental health specialists work together to treat patients with this disorder.

Diagnosis

Chronic pain is diagnosed over time. The diagnosis is based on the patient's history of symptoms, the underlying condition, physical and neurological examination, and diagnostic tests. Patients may be referred to several medical practitioners (e.g., neurologist, orthopedist) for diagnosis and treatment.

Diagnostic tests vary, depending on the underlying condition. Tests may include the following:

• Blood and urine tests
• Imaging tests (e.g., x-ray, CT scan, MRI scan, bone scan)
• Spinal tap (lumbar puncture; may used to diagnose infection, MS, or other conditions)

Electrophysiological studies of the nerves and muscles (e.g., electromyography [EMG], nerve conduction velocity studies) also may be performed. These tests often are used in combination and are referred to as EMG/NCV studies. They are used to rule out or diagnose conditions that affect the nerves or muscles. EMG records electrical activity in muscle tissue, and nerve conduction velocity studies record the speed at which impulses travel through nerves and measure electrical responses.

Thermography measures the temperature of surface tissue as a function of blood flow. This test may be used to detect altered blood flow to a painful area, which may indicate a vascular condition.

Treatment

Treatment for chronic pain depends on the cause and on the individual needs of the patient. Complete pain relief is not always possible; it is important for patients and physicians to work together to find the best treatment plan.

roper exercise can strengthen muscles throughout the body, improve bone strength, reduce the risk for injuries, and enhance feelings of well being. It is important to speak with a doctor before starting an exercise regimen.

Physical therapy and massage therapy can reduce pain, improve function, and prevent recurrences. Other types of treatment that can be used to manage chronic pain include relaxation and behavior modification therapy, meditation, hypnosis, and biofeedback. Spinal manipulation (adjustment) can be used to relieve chronic pain caused by musculoskeletal conditions (e.g., osteoarthritis).

Acupuncture, which involves inserting and manipulating fine needles under the skin at selected points in the body, may be used to relieve chronic pain.

As many as 35% of patients may respond favorably to treatment with a placebo (e.g., sugar pill, saltwater injection). Precisely how a placebo works is unknown. Pain relief may result from the power of suggestion, distraction, or optimism, or from a neurochemical reaction in the brain.

Medications

Over-the-counter analgesics (e.g., aspirin, ibuprofen, acetaminophen) may be used to treat chronic pain. These medications should not be used to relieve pain for longer than 10 days without consulting a physician. Side effects of nonsteroidal anti-inflammatories (NSAIDs) include nausea, abdominal pain, dizziness, and rash. Due to potentially severe gastrointestinal and cardiovascular side effects, NSAIDs should only be used as instructed.

When over-the-counter medications are ineffective, stronger prescription medications may be used. Medications commonly used to treat chronic pain include the following:

• Muscle relaxants (e.g., Zanaflex®)-May cause drowsiness, dry mouth, and constipation.
• Nonsteroidal anti-inflammatories (e.g., Celebrex®)-May cause indigestion, diarrhea, and stomach pain, and severe cardiovascular and gastrointestinal side effects.
• Opioids (e.g., codeine, morphine)-May lead to tolerance, dependence, and addiction.

Duragesic® (fentanyl transdermal system) delivers the opioid analgesic fentanyl through a patch that is worn on the skin. It is used to treat moderate-to-severe chronic pain that does not respond to other medications (e.g., nonopioid analgesics, opioid-acetaminophen combinations) and provides continuous pain relief for 72 hours.

Various doses of the fentanyl transdermal system are available and the dose should be individualized to each patient and evaluated at regular intervals. Duragesic is not used to treat postoperative or acute pain and is not prescribed for children under the age of 12, or patients under the age of 18 who weigh less than 110 lbs.

Duragesic may cause life-threatening hypoventilation (reduced breathing rate and depth of breathing). Repeated administration may result in tolerance and physical and psychological dependence. Other side effects include the following:

• Confusion
• Constipation
• Dry mouth
• Excessive sleepiness (somnolence)
• Excessive sweating
• High blood pressure (hypertension) or low blood pressure (hypotension)
• Nausea and vomiting

Adjuvant drugs may be used to treat chronic pain that does not respond to other pain relievers and to reduce the side effects of other medications. Adjuvant drugs include antidepressants, anticonvulsants, and corticosteroids.

Other Treatments

Other treatment options for chronic pain include the following:

• Neurostimulation
• Corticosteroid injections (may reduce chronic pain caused by inflammation and nerve compression)
• Transcutaneous electrical nerve stimulation (TENS)
• Trigger point injection

Neurostimulation, or brain stimulation, may be used to treat widespread, severe pain. This invasive procedure involves surgically implanting electrodes in the brain, which the patient controls by means of an external transmitter.

In transcutaneous electrical nerve stimulation (TENS), brief pulses of electricity are applied to nerve endings to block pain transmission. This procedure has proven effective for many different types of chronic pain, and is safe and noninvasive.

Surgery (e.g., joint replacement, tumor excision, discectomy) may eliminate some types of chronic pain. Cordotomy may be used in severe cases of lower body pain when other treatments are ineffective. This procedure involves severing the nerve fibers on one or both sides of the spinal cord, eliminating the sensations of pain and temperature.