KEY TERMS

acute pain: sudden, extreme pain that is short-term; serves as a warning of damage or disease

analgesic: a drug or medication that alleviates pain by blocking pain receptors

chronic pain: a deeper, aching pain that comes on slowly and lasts longer than the normal course for a specific injury or condition; it may be constant or intermittent

cutaneous pain: caused by injuries to the skin or superficial tissues; brief and localized

endorphins: brain chemicals released by the body that act as natural painkillers

nociception: the process of transmitting pain messages to the brain through the spinal cord by sensitive nerve endings in skin and tissues

referred pain: pain experienced at a site other than the site of origin

substance P: a peptide found in nerve cells in the body, which serves as a chemical messenger (neurotransmitter) that carries pain messages along pathways to the brain

visceral pain: throbbing or aching pain that originates in the deeper body tissues and organs; of longer duration than cutaneous pain

CAUSES AND SYMPTOMS

Not all causes of pain are known or understood, but some basic causes of the most commonly reported pain include inflammation, as in arthritis, rheumatism, and infection; work-related and sports-related injuries; stress and tension; nerve pain, as from shingles, diabetic neuropathy, and sciatica; and pain related to such diseases as osteoporosis and cancer.

People have similar pain thresholds but different levels of pain tolerance or how much pain they can bear. One congenital anomaly inhibits or eliminates the perception of pain. Pain tolerance is therefore subjective and can be influenced by socioeconomic status, cultural background, and socialization, with disparities noted in who suffers pain, what type of pain a person suffers, and how the individual perceives pain.

Physiological pain is the body’s response associated with tissue damage or inflammation or as a warning system to alert the body to potential physical harm. The most commonly reported types of pain are the lower back, severe or migraine headaches, and joint pain, particularly in the knees. Although pain may be produced without a defined stimulus, such as with emotional or psychological pain, physiological pain is transmitted through stimulation of nerve pathways, a process called “nociception.” Nociceptors are free, sensitive nerve endings outside the spinal column; they are found in skin and internal surfaces, such as on the joints. Nociceptors, when stimulated, send signals through sensory neurons to the posterior horn of the spinal cord that are then transmitted to other nerve fibers, which travel upward through the brain stem to the thalamus, the gateway to conscious action in the brain. There, information is coordinated, localized, and sent to the cerebral cortex, where a conscious reaction to the stimulus is produced.

Pain is said to be referred when it is experienced at a location other than its site of origin. Referred pain occurs when nerve fibers carrying pain messages enter the spinal cord at the same place as other nerve fibers from other body parts using the same pathways. The other nerve fibers may become stimulated and result in painful perceptions in healthy areas of the body, such as referred pain from the heart to the neck, arm, and stomach.

Among theories of pain transmission, Ronald Malzack and Patrick Wall’s Gate Control theory helps explain the differing degrees of pain that people may suffer. It is related to the amount of substance P, a peptide found in nerve cells throughout the body, that reaches the brain. The transmission of neurons is generally very rapid, as touching a hot stove produces immediate action to protect the body from damage. However, messages carried by substance P travel more slowly since they must pass through a special gateway in the spinal cord. At the same time, pain signals also prompt the brain to release chemical endorphins, the body’s natural painkillers, which must descend through the same gate. Thus, there is some competition for passage. The fewer available receptors for substance P once it arrives in the brain, the lower the pain perception. With healing, the gate closes, but when chronic pain occurs, it remains open even after healing or without an identified underlying cause.

The two basic types of pain are acute and chronic. Acute pain comes on suddenly and, although extreme, is generally brief. Acute pain warns the body about damage or disease, is localized, and is more easily treated. Chronic pain, however, occurs daily and lasts longer than would be common for a specific injury. It no longer serves to warn and is much more difficult to treat, although most sufferers can be helped. Chronic pain may last beyond the resolution of an underlying cause or grow out of an acute condition. In this case, it may become a learned response that no longer has a purpose but continues to hurt. Chronic pain may also occur without apparent cause, creating disability, depression, and suffering.

Pain may be medically classified as either superficial or deep. Superficial pain also called “fast or cutaneous pain,” is carried by nerve fibers on the skin and outer linings of the organs. These nerve fibers are plentiful in the intestines, cornea, and nose, for example, and pain messages are quickly delivered to the brain, such as when one is cut or burned. Also termed somatic pain, it is experienced as intense or burning. Kidney stones or acid reflux from the stomach may create waves of this burning pain. Deep pain, on the other hand, also referred to as slow or visceral pain, comes from nerve fibers located in muscles, bones, and tissues of the internal organs. It travels more slowly, taking longer to reach the brain. It may be experienced as dull aching or throbbing pain. The two types of pain may also occur at the same time.

TREATMENT AND THERAPY

The major treatment for pain in the United States has been analgesic medications or drug therapy. Sufferers spend over an estimated $18 billion annually for relief from prescription and over-the-counter medications. There are no standard guidelines for analgesics since the degree of relief varies from patient to patient. These medications are classified as narcotics, such as morphine or opium-based addictive drugs, and nonnarcotic, such as aspirin, ibuprofen, and acetaminophen. Since patients respond differently, and many analgesics can carry significant side effects with cardiovascular, renal, and gastrointestinal toxicity, the lowest dose of the preferred medication is usually recommended to start. Painkillers must also often be administered with other medications directed to the underlying cause of the pain and must therefore be compatible.

One subcategory of nonnarcotic analgesics comprises nonsteroidal anti-inflammatory drugs (NSAIDs). Another alternative, acetaminophen, addresses pain but does not affect inflammation. Another nonnarcotic class of drugs, known as “COX-2 inhibitors,” suppresses the COX-2 enzyme, which triggers inflammation. Although these drugs are seemingly well-tolerated and effective, many endanger the heart, and several were withdrawn from the market.

Narcotic analgesics are the most effective, but long-term use can create dependency. These drugs are stringently protected in the United States by state and federal laws. Doctors have therefore been hesitant to use them for severe chronic pain, even in patients dying from cancer or other painful diseases, when other medications are not working. This situation appears to be changing.

Nondrug therapies include such techniques as transcutaneous electrical nerve stimulation (TENS), massage therapy, neurosurgery, physical therapy and exercise, and mind-body therapies such as guided imagery, meditation, relaxation, and hypnosis. These therapies attempt to alleviate chronic pain in various ways by stimulating blood circulation, blocking nerve pain messengers, and enlisting the help of the brain, where pain messages are processed.

A combination of biomedical and nonbiomedical therapies also utilizes several alternative therapies for pain. Acupuncture and acupressure, the foundation of Chinese medicine, are thought to stimulate blood circulation and possibly the autonomic nervous system by inserting very fine needles at crucial points in the body. Herbal medicine uses substances derived from plants with therapeutic or pharmacologic properties and benefits. Many of today’s medicines have ingredients that originated in plants and can be synthesized in the laboratory. Guided imagery, aromatherapy, creative arts therapy, magnet therapy, and therapeutic touch are often used as adjuncts to dealing with pain, but most have not been proven. Like analgesics, these therapies address the control and management of pain rather than offering a cure.

Although many of these complementary therapies are not biomedically sanctioned or recognized, many chronic pain sufferers try some form of complementary medicine. Little or no research has been done on many of these therapies. Still, their popularity relates to chronic pain being closely connected with the brain, affecting emotions, attitudes, and psychological stability, which are not addressed by conventional medicine and treatment. Some of these therapies may work through the placebo effect, meaning that if one expects the therapy to alleviate pain, it will. Some approaches are backed by positive evidence, while others have no effect. Very little evidence exists about how or why many of these therapies are successful, but combination therapies are vital in alleviating pain; however, they may work.

PERSPECTIVE AND PROSPECTS

The development of pain medicine and clinics devoted solely to the study and alleviation of pain is fairly recent. Since pain was traditionally seen as a symptom rather than a disease or condition in itself, the medical profession has generally focused on treating the cause, considering it purely a diagnostic tool. However, the discovery and development of anesthetics for surgical procedures in the mid-nineteenth century was a huge advance in medical care and treatment and was a precondition for the later development of pain medicine. Anesthesiologists not only had to address traumatic and postoperative pain but also worked to refine techniques and developed expertise in management relating to other types of pain.

Anesthesiology progressed rapidly during World War II, with improved nerve blocking and analgesic use. Anesthesiologist John Bonica contributed significantly to this development of pain medicine. He was faced with extreme, intractable, complex, and phantom limb pain (the sensation of pain felt in a limb no longer there) in the injured during wartime and lacked knowledge or methods to treat them. As pain persisted and physiological causes could not be identified, it became necessary to look elsewhere for the source of the pain. It became obvious that numerous specialists, including psychologists and psychiatrists, needed to consult and discuss their varied findings and opinions.

As defined by the American Academy of Pain Medicine, the specialty concerns the study, prevention, evaluation, treatment, and rehabilitation of people in pain. Practitioners of pain medicine mostly come from other medical fields most closely related to pain, such as neurology, anesthesiology, and rehabilitation. Many are certified as pain specialists through the American Board of Anesthesiology. While some pain clinics focus on specific types of pain, such as bone and joint, others address a broader spectrum of suffering and tend to use various methods and treatments, including alternative therapies, to find whatever works. Some pain cannot be eliminated but can be minimized or controlled to allow the patient to function.

The need to study and understand the causes and alleviation of pain have become more urgent. According to the National Center for Health Statistics, one in four adults in the United States reported suffering pain lasting for at least twenty-four hours during the previous month. One in ten reported pain lasting a year or more. Pain is usually seen as a result of another physical condition. Still, considering the costs that accompany pain and resulting disability in dollars and loss of individual function reflected in absenteeism in the workplace, pain places an increasing burden on the American health-care system. The general cost of pain and pain-related items is estimated to top $100 billion annually.

Research is being conducted into the origins and mechanics of pain to identify new and more effective therapies. A study funded by the National Institutes of Health found that the perception of pain (the extent to which one feels pain) is inherited through a gene with a specific variant. This gene variant affects sensitivity to acute pain and the risk of developing chronic pain. Other genes may also play a role. This study opens up pathways for developing new treatments and approaches to pain.

Such professional organizations as the American Academy of Pain Medicine, the American Pain Foundation, the American Pain Society, and the International Association for the Study of Pain represent only a few of the growing number of resources for studying pain and pain management. Alternative approaches are represented through organizations for specific therapies and the National Center for Complementary and Alternative Medicine.

Further Reading