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Pain and Painkillers (Part II)

By Salvador Quiroz

Pain is an unpleasant sensation localized to a part of the body. It is often described as a stabbing, burning, twisting, oppressing, tearing or squeezing sensation. It is often described as a bodily or emotional reaction, often called terrifying, nauseating, or sickening.

A pain of even higher intensity is usually accompanied by anxiety and the urge to escape or terminate the feeling. These properties illustrate the duality of pain: it is both sensation and emotion. When it is acute and intense, pain is characteristically associated with behavioral arousal and a stress response consisting of increased blood pressure, heart rate, pupil diameter, and levels of cortisones in the blood.

The task of medicine is to preserve and restore health and to relieve suffering. Understanding pain is essential to both of these goals. Because pain is universally understood as a signal of disease, it is the most common symptom that brings a patient to a physician’s attention. But because of the duality of pain, the threshold for this symptom is very personal and has a great degree of variability. In other words, everybody suffers from pain (even masochists), but the degree of suffering depends on the person. Pain is a symptom; fever is a sign. Signs are objective and symptoms like pain are perceived by the physician only through the narrative of the patient. Thus, if you are a good actor, you can malinger with pain because, so far, we do not have a pain-o-meter at our disposal. But when pain is intense, a good physician looks for the other signs mentioned above, such as increase in heart rate, pupil dilation, and/or mild hypertension. Because pain is so intimate a sensation, fakes abound, but very few can escape the eye of a trained physician.

The function of the pain sensory system is to detect, localize, and identify tissue-damaging processes. Since different diseases produce characteristic patterns of tissue damage, the quality, time course, location, and spread of a patient’s pain provide important diagnostic clues and are used to evaluate the response to treatment.

We all know that the pain produced by similar injuries is remarkably variable in different situations and in different people. For example, athletes have been known to sustain serious fractures with only minor pain, and Beecker’s classic WWII survey revealed that many men were not bothered by battle injuries that would have produced agonizing pain in civilian patients. Furthermore, even the suggestion of relief (placebo) has a significant analgesic effect. On the other hand, many patients find even minor injuries (such as vein puncture), unbearable, and the expectation of pain has been demonstrated to induce pain without the painful stimulus itself (for example, listening to the dentist’s drill).

The powerful effect of expectation and other psychological variables on the perceived intensity of pain implies the existence of brain circuits that can modulate the activity of the pain transmission pathways. Although there are probably several circuits, only one has been studied satisfactorily. It has links in certain anatomical sites of the brain, the hypothalamus, the midbrain, and the medulla.

Next week, I will write about the pain modulating circuit and how it contributes to the pain-relieving effect of narcotic analgesic medications. Stay tuned!

Dr Salvador Quiroz, Internal Medicine and Kidney Disease, Hospital H+, Graduated from the Mayo Clinic. Tel: 152 2329


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