Tuesday, 9 November 2010

Chronic Pain: A Disease in its Own Right

Melanie Thernstrom has written a superb book based on a historical, philosophical, and scientific review of pain: The Pain Chronicles: Cures, Myths, Mysteries, Prayers, Diaries, Brain Scans, Healing, and the Science of Suffering. Herself a victim of chronic pain, she brings a personal perspective to the subject and also includes informative vignettes of doctors and patients she encountered at the many pain clinics she visited in her investigations. She shows that medical treatment of pain is suboptimal because most doctors have not yet incorporated recent scientific discoveries into their thinking, discoveries indicating that chronic pain is a disease in its own right, a state of pathological pain sensitivity.

Chronic pain often outlives its original causes, worsens over time, and takes on a puzzling life of its own… there is increasing evidence that over time, untreated pain eventually rewrites the central nervous system, causing pathological changes to the brain and spinal cord, and that these in turn cause greater pain. Even more disturbingly, recent evidence suggests that prolonged pain actually damages parts of the brain, including those involved in cognition.

Sometimes the original problem creates new ones as the patient distorts posture and avoids exercise in an attempt to reduce the pain.  In chronic pain, the protective mechanism of avoidance becomes maladaptive. Muscles atrophy from disuse and new sources of pain develop. Jerome Groopman, MD, in The Anatomy of Hope, told how he conquered years of chronic back pain by realizing that his pain was not a warning to avoid further damage but a false message that he could refuse to listen to; with exercise and physical therapy he rebuilt his muscles and became pain-free.

Dr. John Sarno believes that chronic musculoskeletal pain is a manifestation of “tension myositis syndrome” due to repressed negative emotions. He recommends renouncing all treatments, accepting that pain is only in the mind, and resuming normal activities. I don’t accept his psychosomatic premise, but there is a grain of truth in his method. If patients can re-frame their thinking and resume normal activities despite the pain, they are more likely to improve than if they maintain the self-image of a sick, disabled victim.

Distraction is effective in removing the awareness of pain. Thernstrom tells us that as she got better,

I wasn’t aware of being in pain all the time, but whenever I thought about whether I had pain, I always did. There were pain-free moments owing to my being preoccupied — happily or unhappily — with something else, but I was never able to “catch” a pain-free moment and enjoy it, which meant that, in some sense, I was always in pain.

Pain perception in the brain involves two different pain systems: one of pain perception and one of pain modulation. Acute injuries always hurt more later as the modulation effects diminish and the brain releases neurotransmitters into the spinal cord that amplify incoming signals and augment pain. This serves the adaptive purpose of enabling flight at first and then enforcing rest. It is possible to induce complete analgesia in humans and animals by electrically stimulating pain-modulating areas of the brain. Various cognitive and affective states activate the two systems, especially attention and expectation. Simply asking patients to think about their pain activates the pain-perception circuits. Anticipation of a placebo effect causes the pain-modulating release of endorphins in the brain.

One medication requires the placebo effect for all of its effectiveness. An intriguing 1995 clinical trial proved an analgesic called proglumide to be a more effective pain reliever than a placebo when both groups were told they were being given an exciting new painkiller. But then subjects were slipped proglumide without their knowledge, thus ensuring they had no placebo effect, they felt no relief at all. None.

It turns out proglumide enhances the endorphin response by blocking cholecystokinin receptors.  Thernstrom speculates that drugs could be designed to enhance or create a placebo effect. Hmm… what would medical ethicists have to say about that? For that matter, how can a treatment still be called a placebo if it is shown to have the effect of producing endorphins in the brain?

Opioids relieve pain, but they are both under-used and over-used. If acute pain were better controlled, fewer patients would develop chronic pain. On the other hand, many chronic pain patients develop opioid-induced hyperalgesia, where their body becomes more sensitive to pain stimuli or even ordinary stimuli; they develop pain in parts of their bodies remote from the original injury site.

Caution is required. Relieving pain sometimes causes harm. A phase 3 study of tanezumab was recently halted by the FDA. Although the drug relieved the pain of osteoarthritis, it also resulted in more joint failure, presumably because there was more wear and tear on the joints when pain was absent.

The Pain Chronicles is a fascinating glimpse into the world of pain sufferers as well as a good overview of our current scientific knowledge. It suggests avenues of investigation that may vastly improve our management of pain. I highly recommend it to anyone who wants to know more about any aspect of the pain experience and the science.

I am always interested in reading and hearing about individual's experiences. This could be a worthwhile insight.

Posted via email from Specialist Pain Physio

1 comment:

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