The Perception of Pain

Dixie Morgan

Stephen F. Austin State University, Spring 2000

Return to Perception: Spring 2000frontpage.

At some point in life, all people experience pain. The presence ofpain can prevent further damage to an injured area or even prevent aninjury from occurring, but pain that continues, after treatment oreven after healing, can be debilitating (Loeser and Melzack, 1999).

Stephani Curtis (1997) presents a case study of a 32-year-oldwoman, Mrs. J, who injured her lower back when she fell off a horse.As a result of this accident, Mrs. J experienced a ruptured lumbardisc. The treatment, a lumbar laminectomy, failed to alleviate herpain. Due to the pain and the effects of her prescribed medication,Mrs. J was forced to curtail her activities, and she had to quit herjob as a truck driver. Psychologists, neurosurgeons, and otherhealth-care professionals research to relieve pain for patients likeMrs. J. This much needed research offers hope for the millions ofpeople whose lives have been disrupted by pain, such as chronic pain,hyperalgesia, and allodynia.

While pain has always been present in humans' lives, Loeser andMelzack (1999) report that it is in only the past 30 years that painresearch has made advances in both the treatment and theunderstanding of pain. There are three basic categories of pain:transient, acute, and chronic.

Short-term, or transient pain, serves to protect an individualfrom any lasting damage. Nociceptive transducers activate thisbeneficial kind of pain in daily life when people stub a toe or get amild sunburn. People rarely seek medical care to address transientpain symptoms. The pain itself motivates the person to stop theharmful activity to prevent additional pain and damaging injury.

When damage does occur to an injured area, nociceptive transducersalso activate acute pain, another beneficial type of pain. A brokenbone or a tissue-damaging burn are examples of this medium-durationpain. People normally go to the doctor to aid the natural healing ofthe body and to reduce pain. Acute pain rarely continues for longerthan three months; although, continuous acute pain from malignantdiseases can last longer.

The final category of pain, chronic, presents many challenges toboth patients, like Mrs. J, and health-care providers. The pain failsto cease after treatment or even after healing in some cases. Thebody may be unable to heal as in the amputation of a limb. Painexperienced in the missing limb is known as phantom limb pain (Loeserand Melzack, 1999; Pain Drain, 1999). Additionally, researchers thinkthat the brain's plasticity allows experience to change the brain'sprocessing of pain (Iadarola and Caudle, 1997). Although patientsalmost always seek medical intervention for chronic pain, the needfor more effective treatments and for ways of addressing a patient'spain symptoms has caused medical professionals to be unable toeffectively alleviate their patients pain in many cases (Loeser,, 1999; Pain Drain, 1999).

The costs related to chronic pain are enormous. Leigh, Markowitz,Fahs, Shin, and Landrigan found for the year 1992, Americans sufferedover 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 fromwork-related diseases which cost another $25.5 billion and brings thetotal cost to $170.5 billion.

One example of a costly and debilitating work-related injury iscarpal tunnel syndrome, a repetitive motion disorder. Atcheson, Ward,and Lowe (1998), in an observational study of 297 patients, foundthat disease and occupation seem to be independently associated withcarpal tunnel syndrome. They suggest that doctors approach treatmentby addressing both work-related factors and underlying diseases suchas hypothyroidism. Regardless of the effect of certain diseases oncarpal tunnel syndrome, repetitive work motions may trigger and/oraggravate the patient's health. Carpal tunnel syndrome can bedisabling and/or can cause permanent damage. Technological approachesto providing a less harmful work environment, such as ergonomickeyboards and mouse wrist protectors, may help reduce additionalaggravation while researchers continue to study this debilitatingdisorder.

In addition to efforts to understand chronic and other types ofpain, researchers are also looking for more effective treatments.Doctors frequently prescribe medication as a part or as the whole ofthe treatment of pain. They must carefully consider a variety of sideeffects caused by drugs. For example, when aspirin is taken for along time, it may counteract the body's natural prostaglandinseffect. The patient also increases the possibility of developing apeptic ulcer or gastro-intestinal bleeding. Other dangers exist inpharmaceutical treatment. Some medications are addictive; others maycause dizziness, constipation, or blurred vision. Morphine can causemore pain in some people rather than reducing pain (Pain Drain,1999).

Heger, Maier, Otter, Helwig, and Suttorp (1999) examine the effectof morphine in causing hyperalgesia and allodynia. Hyperalgesiahappens when a patient feels more pain than normal for a painfulevent. When a patient experiences pain from a stimulus, such astouch, that is normally painless, allodynia occurs (Pain Drain,1999). Anyone who has ever taken a warm shower when he had a sunburnhas a little idea of what allodynia is like. While these effects havebeen observed in adults and children, a 9-month-old girl with a braintumor was the first case of hyperalgesia and allodynia due tomorphine exposure in a baby. The child was given morphine to reducethe pain she experienced during even routine nursing. The dosage wasincreased when she continued to cry and to exhibit extreme discomfortduring daily care chores. Even feeding caused discomfort to thechild. The morphine dosage was reduced when the doctors suspectedallodynia and hyperalgesia due to the use of morphine. They changedher medication, and she quickly improved. She remained pain free forthe 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 aruptured lumbar disc. After its removal, Mrs. J tried a variety ofother treatments including physical therapy, exercises, and analgesicmedication because she continued to experience pain. She, then,received a lumbar facet radio-frequency lesioning procedure. Aftertwo weeks, she was feeling well enough to go back to work. She waspain free after six months, and she did return to being a truckdriver (Curtis, 1997).

Research is continuing into pharmacological and surgicalapproaches for alleviating chronic pain without affecting acute pain.Iadarola and Caudle (1997) explain that after as little as 5 or 10minutes of pain, the brain and neural system begin to change. Whilethese changes are not completely understood, research has shown thatthese changes alter genes that are responsible for encodingneuropeptides as part of a transcriptional network. If the paincontinues for a long time, more genetic alteration occurs. One suchstudy by Mantyh, et. al. (1997) examined the role of substance P innociceptive signaling. They discovered that it is instrumental in thetranscriptional network relaying pain including hyperalgesia. Theycut, or ablated, specific neurons in lamina I of mice. The miceexhibited a reduction in chronic, or persistent, pain without losingacute pain. While this research promises hope for millions who sufferfrom chronic pain, continued research in this area is required beforethis kind of treatment can be used for therapy in humans. Researchersneed to examine the long term effects of permanently destroyingneurons.

While morphine can induce hyperalgesia and allodynia, these twoeffects 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] isconcentrated in lamina II with some in lamina I, where Mantyh, (1997) ablated neurons in mice. Malmberg, et. al. discovered thatthe mice lacking PKC [Gamma] did not suffer from neuropathic painfollowing sciatic nerve injury; however, they continued to experienceacute pain.

In a study by Eguchi, et. al. (1999) found that prostaglandinplays a part in nociception. Prostaglandin D2(PGD2) is necessary in allodynia. Mice injected with anendogenous pain-producing substance, PGE2, did notexperience allodynia; however the mice did experience thermalhyperalgesia. This complex relationship between PGD2 andPGE2 requires additional study, but this research iscontributing to the growing understanding of pain perception.

Humans need pain to alert them to injury and damage to theirbodies. They may experience a variety of different pains in theirdaily lives, but when pain continues for a long time, people's livesare disrupted. The medical costs compound with the cost of job lossto result in an enormous expense that affects millions of Americanseach year. Additionally, depression may set in as patients are forcedto curtail social activities, to quit work, and to endure continuingpain. Researchers are working to expand their knowledge of how humansperceive pain and how to effectively eliminate debilitating chronicpain without destroying the perception of transient and acute pain.As the studies in this paper reveal, researchers are discovering avariety of factors that contribute to pain and new treatments thatallow 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 painfree, and many others are benefitting from the various applicationsof research to surgical and pharmacological treatments. Continuedresearch must be done to understand how to stop chronic pain withoutaffecting acute pain and without doing additional harm to thepatient. Researchers also can look into ways to apply these findingsto constructing tools to stop aggravating painful conditions. Whilethe major advances in nociception and pain research have occurredduring only the past 30 years, these advances promise new hope forthe millions of Americans who endure chronic pain.


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