Dixie Morgan
Stephen F. Austin State University, Spring 2000
Return to Perception: Spring 2000 frontpage.
At some point in life, all people experience pain. The presence of pain can prevent further damage to an injured area or even prevent an injury from occurring, but pain that continues, after treatment or even after healing, can be debilitating (Loeser and Melzack, 1999).
Stephani Curtis (1997) presents a case study of a 32-year-old woman, Mrs. J, who injured her lower back when she fell off a horse. As a result of this accident, Mrs. J experienced a ruptured lumbar disc. The treatment, a lumbar laminectomy, failed to alleviate her pain. Due to the pain and the effects of her prescribed medication, Mrs. J was forced to curtail her activities, and she had to quit her job as a truck driver. Psychologists, neurosurgeons, and other health-care professionals research to relieve pain for patients like Mrs. J. This much needed research offers hope for the millions of people whose lives have been disrupted by pain, such as chronic pain, hyperalgesia, and allodynia.
While pain has always been present in humans' lives, Loeser and Melzack (1999) report that it is in only the past 30 years that pain research has made advances in both the treatment and the understanding of pain. There are three basic categories of pain: transient, acute, and chronic.
Short-term, or transient pain, serves to protect an individual from any lasting damage. Nociceptive transducers activate this beneficial kind of pain in daily life when people stub a toe or get a mild sunburn. People rarely seek medical care to address transient pain symptoms. The pain itself motivates the person to stop the harmful activity to prevent additional pain and damaging injury.
When damage does occur to an injured area, nociceptive transducers also activate acute pain, another beneficial type of pain. A broken bone or a tissue-damaging burn are examples of this medium-duration pain. People normally go to the doctor to aid the natural healing of the body and to reduce pain. Acute pain rarely continues for longer than three months; although, continuous acute pain from malignant diseases can last longer.
The final category of pain, chronic, presents many challenges to both patients, like Mrs. J, and health-care providers. The pain fails to cease after treatment or even after healing in some cases. The body may be unable to heal as in the amputation of a limb. Pain experienced in the missing limb is known as phantom limb pain (Loeser and Melzack, 1999; Pain Drain, 1999). Additionally, researchers think that the brain's plasticity allows experience to change the brain's processing of pain (Iadarola and Caudle, 1997). Although patients almost always seek medical intervention for chronic pain, the need for more effective treatments and for ways of addressing a patient's pain symptoms has caused medical professionals to be unable to effectively alleviate their patients pain in many cases (Loeser, et. al., 1999; Pain Drain, 1999).
The costs related to chronic pain are enormous. Leigh, Markowitz, Fahs, Shin, and Landrigan found for the year 1992, Americans suffered over 13.2 million work-related injuries. These injuries, alone, resulted in $145.37 billion of direct and indirect expenses (Leigh, et. al., 1997). This figure does not include expenses resulting from work-related diseases which cost another $25.5 billion and brings the total cost to $170.5 billion.
One example of a costly and debilitating work-related injury is carpal tunnel syndrome, a repetitive motion disorder. Atcheson, Ward, and Lowe (1998), in an observational study of 297 patients, found that disease and occupation seem to be independently associated with carpal tunnel syndrome. They suggest that doctors approach treatment by addressing both work-related factors and underlying diseases such as hypothyroidism. Regardless of the effect of certain diseases on carpal tunnel syndrome, repetitive work motions may trigger and/or aggravate the patient's health. Carpal tunnel syndrome can be disabling and/or can cause permanent damage. Technological approaches to providing a less harmful work environment, such as ergonomic keyboards and mouse wrist protectors, may help reduce additional aggravation while researchers continue to study this debilitating disorder.
In addition to efforts to understand chronic and other types of pain, researchers are also looking for more effective treatments. Doctors frequently prescribe medication as a part or as the whole of the treatment of pain. They must carefully consider a variety of side effects caused by drugs. For example, when aspirin is taken for a long time, it may counteract the body's natural prostaglandins effect. The patient also increases the possibility of developing a peptic ulcer or gastro-intestinal bleeding. Other dangers exist in pharmaceutical treatment. Some medications are addictive; others may cause dizziness, constipation, or blurred vision. Morphine can cause more pain in some people rather than reducing pain (Pain Drain, 1999).
Heger, Maier, Otter, Helwig, and Suttorp (1999) examine the effect of morphine in causing hyperalgesia and allodynia. Hyperalgesia happens when a patient feels more pain than normal for a painful event. When a patient experiences pain from a stimulus, such as touch, that is normally painless, allodynia occurs (Pain Drain, 1999). Anyone who has ever taken a warm shower when he had a sunburn has a little idea of what allodynia is like. While these effects have been observed in adults and children, a 9-month-old girl with a brain tumor was the first case of hyperalgesia and allodynia due to morphine exposure in a baby. The child was given morphine to reduce the pain she experienced during even routine nursing. The dosage was increased when she continued to cry and to exhibit extreme discomfort during daily care chores. Even feeding caused discomfort to the child. The morphine dosage was reduced when the doctors suspected allodynia and hyperalgesia due to the use of morphine. They changed her medication, and she quickly improved. She remained pain free for the last 17 months of her life (Heger, et. al., 1999; Correction, 1999).
Doctors also perform surgery to treat patients with chronic pain. Mrs. J, mentioned earlier, received a lumbar laminectomy to treat a ruptured lumbar disc. After its removal, Mrs. J tried a variety of other treatments including physical therapy, exercises, and analgesic medication because she continued to experience pain. She, then, received a lumbar facet radio-frequency lesioning procedure. After two weeks, she was feeling well enough to go back to work. She was pain free after six months, and she did return to being a truck driver (Curtis, 1997).
Research is continuing into pharmacological and surgical approaches for alleviating chronic pain without affecting acute pain. Iadarola and Caudle (1997) explain that after as little as 5 or 10 minutes of pain, the brain and neural system begin to change. While these changes are not completely understood, research has shown that these changes alter genes that are responsible for encoding neuropeptides as part of a transcriptional network. If the pain continues for a long time, more genetic alteration occurs. One such study by Mantyh, et. al. (1997) examined the role of substance P in nociceptive signaling. They discovered that it is instrumental in the transcriptional network relaying pain including hyperalgesia. They cut, or ablated, specific neurons in lamina I of mice. The mice exhibited a reduction in chronic, or persistent, pain without losing acute pain. While this research promises hope for millions who suffer from chronic pain, continued research in this area is required before this kind of treatment can be used for therapy in humans. Researchers need to examine the long term effects of permanently destroying neurons.
While morphine can induce hyperalgesia and allodynia, these two effects can also be caused by nerve injury. Malmberg, Chen, Tonegawa, and Basbaum, studied mice that lack protein kinase C gamma (PKC [Gamma]) to better understand neuropathic pain. PKC [Gamma] is concentrated in lamina II with some in lamina I, where Mantyh, et. al. (1997) ablated neurons in mice. Malmberg, et. al. discovered that the mice lacking PKC [Gamma] did not suffer from neuropathic pain following sciatic nerve injury; however, they continued to experience acute pain.
In a study by Eguchi, et. al. (1999) found that prostaglandin plays a part in nociception. Prostaglandin D2 (PGD2) is necessary in allodynia. Mice injected with an endogenous pain-producing substance, PGE2, did not experience allodynia; however the mice did experience thermal hyperalgesia. This complex relationship between PGD2 and PGE2 requires additional study, but this research is contributing to the growing understanding of pain perception.
Humans need pain to alert them to injury and damage to their bodies. They may experience a variety of different pains in their daily lives, but when pain continues for a long time, people's lives are disrupted. The medical costs compound with the cost of job loss to result in an enormous expense that affects millions of Americans each year. Additionally, depression may set in as patients are forced to curtail social activities, to quit work, and to endure continuing pain. Researchers are working to expand their knowledge of how humans perceive pain and how to effectively eliminate debilitating chronic pain without destroying the perception of transient and acute pain. As the studies in this paper reveal, researchers are discovering a variety of factors that contribute to pain and new treatments that allow the patient to be pain free and to return to a productive, working life. Mrs. J, who was able to return to work and be pain free, and many others are benefitting from the various applications of research to surgical and pharmacological treatments. Continued research must be done to understand how to stop chronic pain without affecting acute pain and without doing additional harm to the patient. Researchers also can look into ways to apply these findings to constructing tools to stop aggravating painful conditions. While the major advances in nociception and pain research have occurred during only the past 30 years, these advances promise new hope for the millions of Americans who endure chronic pain.
References
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Correction (to 'Morphine induced allodynia in a child with brain tumour', in September 4, 1999 issue). (1999). British Medical Journal, 319, 1114.
Curtis, S. (1997). Radio-frequency lesioning to treat chronic lumbar facet joint point. AORN Journal, 66, 684.
Eguchi, N., Minami, T., Shirafuji, N., Kanaoka, Y., Tanaka, T., Nagata, A., Yoshida, N., Urade, Y., Ito, S., Hayaishi, O. (1999). Lack of tactile pain (allodynia) in lipocalin-type prostaglandin D synthase-deficient mice. Proceedings of the National Academy of Sciences of the United States, 96, 726.
Heger, S., Maier, C., Otter, K., Helwig, U., Suttorp, M. (1999). Morphine induced allodynia in a child with brain tumour. British Medical Journal, 319, 627.
Iadarola, M. J., Caudle, R. M. (1997). Good pain, Bad pain. Science, 278, 239.
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