How pain becomes chronic

Pain impulses enter the brain from the spinal cord which receives pain nerve signals from the injury site. AlL PAIN IS NEUROLOGICAL

From the injury site, substance P and cytokines, both neurotransmitters, are produced. They are sent into the back of the  spinal cord (called the dorsal horn) via long  nerves.  These nerves are A Delta (fast) and C (slow) fibers which carry information about the site, type and nature of the pain.  

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HOW PAIN BECOMES CHRONIC

Acute pain can become chronic due to a number of factors.  First, scar tissue typically forms around injury sites, and can serve as permanent pain nerve stimulators. Second, some injuries (e.g. spinal disc herniations, broken bones, etc) require the implantation of metal rods & screws for stabilization.  While providing stability, these metals are not inert and have been shown to attract inflammatory cells that cause permanent irritation of surrounding nerves and other tissues.  

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Next, injured joints develop rough articulation surfaces (where the two sides meet and interact in synovial fluid), and these rough surfaces cause progressive joint degeneration and permanent pain.  Finally, some injuries (e.g. crush injuries to limbs) cause tiny nerve nets to be literally re-set, such that pain nerves start responding to things that should not hurt, like wind, touch, and even tepid water.  

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The next time some silly person asks why you still have pain after all these years;  answer them with these words: 

SCAR TISSUE; RESET NERVES; CHRONIC INFLAMMATION, TRAUMATIC ARTHRITIS

and their mother wears combat boots  !!!!!! 

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Just before pain impulses enter the brain they are waylaid in the brain stem, an area just under the brain itself. Once in the brain stem, pain impulses are processed by areas called the reticular system. This produces a chemical, serotonin, which attempts to block pain impulses coming up to the brain.

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Serotonin is produced in brain stem nuclei (bundles of nerves that talk to one another) called raphe nuclei.  These nerve bundles send out nerve fibers and chemical signals that touch the spinothalamic tract that carries pain up toward the brain.  Serotonin nerve fibers also use Vitamin C as a co-factor to produce endomorphins, natural pain killer chemicals. These serotonin fibers and chemicals attempt to block out pain.  

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In addition to the serotonin anti-pain processes in the brain stem, several other events occur when pain transmits through the reticular system.  Throughout the reticular activating system (RAS), there are nuclei called the locus ceruleus;  here, the nerve bundles produce nor-epinephrine, formerly called nor-adrenaline.  

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Just as one might think, these neurotransmitters are stimulatory and result in activation of the widely known "flight or fight syndrome."  This is all fine, when the individual can flee or fight to resolve the situation confronting them.  But, in the case of pain, one cannot flee and one cannot fight it directly ; leaving the person to cope with built up  feelings of hopelessness, anger and angst, that can turn into panic, irritability or dysphoria. 

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Also, in some people this stimulation of the RAS results in surges of nor-epinephrine (noradrenalin) that can cause panic anxiety and cardiac symptoms. 

 In other words, uncontrolled pain can cause panic, chest pain, and abnormal heart rhythms, like skipped beats.

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From the brain stem, pain impulses enter the thalamus and then they are sent to the limbic system and the cortex.

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The thalamus is the way station of the brain, sending signals in various directions.  Pain is sent to the limbic system for emotional processing, and to the cortex for localization (so the brain will know where the pain is coming from).  It is also sent to a part of the brain called the cingulate, which controls pain memories.  Then, from the cortex, there is a nerve tract called the  cortico-spinal tract.  It is sent DOWN to attempt to block pain.  

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Without the serotonin, endomorphins and cortico-spinal mechanisms of reducing pain, the individual would probably be unable to tolerate pure, un-adulterated, pain impulses.  Some people seem to have more of these anti-pain systems than others, and some have less, unfortunately.  

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The unfortunate people who have weak or damaged anti-pain systems are likely locked in to chronic pain, and require long term medication management of pain.  

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This basically boils down to genetics.  Some people have a genetic predisposition to high pain tolerance; others to a low pain tolerance.  Those with a genetically disposed  low pain tolerance are likely to be pre-disposed to the development of chronic pain from injuries, surgeries, and pathological processes such as arthritis.  

Others who are more fortunate, have high tolerance for pain until their anti-pain systems are overwhelmed, usually via trauma,  by chronic, unremitting and horrendous pain !!

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In  other words, some types of pain have the ability to over-ride and overwhelm the individual's natural anti-pain systems.   Some types of injuries can also damage the anti-pain systems noted above. 

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Body's defenses against pain

Serotonin in the raphe nucleus blocks some of the pain signals coming up from below. Low serotonin yields more pain (and depression); this is why many people with chronic pain become depressed, their bodies have used up serotonin trying to control pain.......................... Somewhat opposite this process, is when pain impulses from below stimulate different parts of the brain stem's reticular activating system and cause hyper-arousal in an attempt to induce the FIGHT OR FLIGHT response. This may result in, with some people, the development of pain induced anxiety and panic disorders.

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The cortico-spinal tract goes down from the brain and into the spinal cord to inhibit pain signals coming up from the periphery.  For example it blocks any  signals coming up from the cord, arms, legs and trunk.  This is one way the brain can naturally dampen pain, in addition to the serotonin anti-pain actions in the brain stem.  

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Various drugs act at different sites to either block pain that's coming up or enhance pain control that's going down the spinal cord. ____________________

Opiates act at the brain and spinal cord, neuromodulators (e.g. gabapentin, pregabalin, et. al) act at the brain, brain stem, and dorsal horn of the spinal cord.  NSAIDs act at the local trauma site.  Anesthetics, such as lidocaine, act at both the trauma site and where the peripheral nerve carrying pain enters the spinal cord.  Antidepressants act at the Raphe tracts in the brain stem. Antispasmodics act at the junction of peripheral nerves and muscle to block pain stemming from muscle spasm.

It should now be abundantly clear to the reader that effective management of pain requires a Pain Physician with in depth knowledge of the brain, the brain stem, the spinal cord, and injury sites, as well as their inter-locking neurochemistry, neuroanatomy, and neuro-psychopharmacology

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 Always remember, the pain is not in your head, its in your neurons, your neuro-circuitry, and your neurochemistry!


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Recall that you can access Dr. Workman's recent Pain Medicine lecture to Medicine residents at UT Medical Center, via the image on the prior page.

Files Coming soon: Vitamin C as an opiate sparing agent;  Pain and Diet: Do you have an inflammatory diet?; Auricular Acupressure: Effects on Pain. 

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