Chronic Pain

CHRONIC PAIN

Chronic or persistent pain is defined as pain that lasts for longer than six months. Chronic pain can stem from cancer, illness, injury, or postsurgical changes. Often, persons with chronic pain suffer from syndromes that cannot be confirmed by laboratory tests. These chronic pain syndromes include central pain syndromes, fibromyalgia, headache, lower back pain, myofascial pain syndrome, neuropathic pain, and phantom limb pain. Frequent locations of chronic pain include the back, head, joints, chest, abdomen, and extremities. Chronic pain is common and its sufferers are more likely to have anxiety or depression, have poor perception of their health, decreases in their quality of life, and experience a disruption of their livelihood than those who are not in pain.

In most cases, there is no cure for the chronic pain so treatment is aimed at pain control and rehabilitation. Unfortunately, chronic pain is often ineffectively treated because physicians can be reluctant to prescribe strong, potentially addictive medications. The ineffective pain treatment is compounded by commonly associated conditions such as depression, insomnia, fatigue, and a decrease in general physical functioning. Therefore, treating the pain alone is not sufficient.

The optimal approach to the chronic pain sufferer is an interdisciplinary team that may be comprised of a pain management physician, nurse specialist, psychologist, physical therapist, pharmacist, and vocational counselor. The physician conducts a thorough assessment of the patient and determines the appropriate medical interventions. The psychologist conducts a thorough psychological assessment, educates the patient on techniques to reduce pain, and tends to any associated mental health illnesses. The nurse specialist acts as a case manager and educator. The physical therapist ascertains the patient's physical endurance, flexibility, and strength and conducts the physical rehabilitation process. The vocational counselor identifies and devises strategies to allow the patient to return to work. In addition to dispensing medications, the pharmacist will review past and present use of medicinal agents and educate the patient on the proper use of medications.

PHARMACOLOGICAL MANAGEMENT OF CHRONIC PAIN

In the treatment of chronic pain, drugs (analgesics) are usually administered in a stepwise fashion beginning with mild, relatively safe agents and progressing to stronger agents as necessary. In 1986, the World Health Organization (WHO) proposed a stepwise plan, frequently called the Analgesic Ladder, for the oral treatment of cancer pain. This plan provides adequate pain relief for up to 90 percent of cancer patients but may have limited success for other chronic pain patients. Step one of the ladder is recommended for patients with mild pain and consists of nonopioid analgesics, step two is for moderate pain and consists of mild opioids, and step three is for severe pain and consists of strong opioids. More than one analgesic may be used at a time for an added effect, a procedure called adjuvant therapy.

Nonopioid analgesics consist of acetaminophen and nonsteroidal anti-inflammatory drugs (NSAIDs). Acetaminophen is an effective analgesic that has a minimal side effect profile. Nonsteroidal anti-inflammatory drugs have both analgesic and anti-inflammatory properties. Examples of nonsteroidal anti-inflammatory drugs are aspirin, ibuprofen, naproxen, meclofenamate, piroxicam, and more recently celebrex and vioxx. Major side effects associated with the use of nonsteroidal anti-inflammatory drugs include kidney toxicity, bleeding disorders, and stomach disorders.

Opioid analgesics are available in different strengths. Examples of opioid analgesics are morphine, fentanyl, methadone, and meperidine. The side effects of opioids may be much more serious than those seen with nonopioid analgesics. Side effects include respiratory depression, alterations in consciousness (e.g. drowsiness, sedation, confusion), nausea, vomiting, constipation, urinary retention, and itching.

Other medications used in the treatment of chronic pain include antidepressants and anticonvulsants. Nerve blocks, injection of anesthetics into trigger points, or injection of steroids into the epidural space of the spinal cord may also be utilized. Implantable methods are utilized as treatments of last resort. These methods involve implanting drug delivery systems or electrodes into specific areas of the spinal cord.

TOLERANCE, DEPENDENCE, AND ADDICTION

The continued use of opioids leads to tolerance, in which increasingly higher doses of drug must be used to obtain the original level of pain relief. Tolerance develops slowly, occurring over a period of months to years. Cross-tolerance to other opioids develops, although to a lesser extent. Tolerance can be differentiated from physical dependence and addiction.

Physical dependence is a characteristic of opioid use because of the mode of action. It reflects a state of neurological adaptation to the drug. With physical dependency, discontinuation of opioid use leads to withdrawal symptoms (e.g. sweating, tearing, rapid heart rate, nasal discharge, abdominal cramps, nausea, and vomiting). To prevent withdrawal symptoms, patients on long term opioid use are gradually weaned off the medication. Physical dependence on opioids does not lead to addiction, although it may compel the patient to seek opioids to relieve symptoms of withdrawal.

For chronic pain patients taking opioids, tolerance and physical dependence are not indicators of addiction. Addiction is not a characteristic of opioid use, rather, it is dependent upon the user. In fact, the medical use of opioids is only very rarely associated with addiction. The agonist-antagonist class of opioids (buprenorphine, butorphanol, nalbuphine, pentazocine, and dezocine) has a low abuse potential.

Any patient taking opioids to treat chronic pain can meet the criteria for addiction set forth by the American Psychiatric Association in the Diagnostic and statistical manual of mental disorders: DSMIV. Therefore, it is very difficult to diagnose addiction in chronic pain patients who are taking opioids. Chronic pain patients who are being ineffectively treated could display the drug-seeking behavior that is characteristic of addiction, a phenomenon called pseudoaddiction . Alternatively, the patient receiving effective pain treatment may take extreme measures to insure an adequate supply of medication. This behavior is termed therapeutic dependence .

Suggestive signs of addiction within the context of opioid therapy for chronic pain include:

• Loss of control over opioid use;
• Preoccupation with the use of opioids despite adequate pain control; and
• Continued use of opioids even with their adverse consequences.

BIBLIOGRAPHY

Ashburn, M.A. & Rice, L. J. (1998). The Management of Pain. New York, NY: Churchill Livingstone.

Ashburn, M.A. & Staats, P. S. (1999). Management of chronic pain. Lancet, 353, 1865-1869.

Gallagher, R.M. (ed.) (1999). The medical clinics of North America: Chronic pain. Philadelphia, PA: W. B. Saunders Company.

Belinda Rowland