THE BIOCHEMICAL ORIGIN OF PAINby Sota Omoigui

CHAPTER 1

SOTA OMOIGUI’S LAW OF PAIN. The origin of all pain is inflammation and the inflammatory response.

Irrespective of the type of pain whether it is acute pain as in a sprain, sports injury or eurochange jellyfish sting or whether it is chronic pain as in arthritis, migraine, back or neck pain from herniated disks, RSD/CRPS pain, Fibromyalgia, Interstitial cystitis, Neuropathic pain, Post-stroke pain etc, the underlying basis is inflammation and the inflammatory response. Irrespective of the characteristic of the pain, whether it is sharp, dull, aching, burning, stabbing, numbing or tingling, all pain arise from inflammation and the inflammatory response.

The current theories and treatment options for persistent pain are not satisfactory. The population of patients with chronic pain and disrupted lives grows constantly. According to the American Pain foundation, there are 75 million Americans who have chronic pain. Pain is the second most common reason for doctor visits. Unless we can understand how pain is generated, we cannot provide a solution. Current medical theories place an over reliance on structural abnormalities to explain pain syndromes. This is not surprising because our current imaging technologies are structure based. Physicians are comfortable treating what they see. Patients who have structural abnormalities such as a herniated disk on MRI scans get operated upon often times needlessly and end up with more back or neck pain. Patients with severe pain who do not have structural abnormalities on MRI scans are dismissed as psychiatric cases. The fallacy of this approach has been confirmed in numerous published studies. In one of these studies [2][1], the authors performed magnetic resonance imaging on sixty-seven individuals who had never had low-back pain, sciatica, or neurogenic claudication. The scans were interpreted independently by three neuro-radiologists who had no knowledge about the presence or absence of clinical symptoms in the subjects. About one-third of the subjects were found to have a substantial abnormality. Of those who were less than sixty years old, 20 per cent had a herniated nucleus pulposus and one had spinal stenosis. In the group that was sixty years old or older, the findings were abnormal on about 57 per cent of the scans: 36 per cent of the subjects had a herniated nucleus pulposus and 21 per cent had spinal stenosis. There was degeneration or bulging of a disc at least one lumbar level in 35 per cent of the subjects between twenty and thirty-nine years old and in all but one of the sixty to eighty-year-old subjects. In view of these findings in asymptomatic subjects, the authors concluded that abnormalities on magnetic resonance images must be strictly correlated with age and any clinical signs and symptoms before operative treatment is contemplated. In another study [3][2], the authors examined the prevalence of abnormal findings on magnetic resonance imaging (MRI) scans of the lumbar spine in people without back pain. 52 percent of the asymptomatic subjects were found to have a bulge at least at one level, 27 percent had a protrusion, and 1 percent had an extrusion. Thirty-eight percent had an abnormality of more than one intervertebral disk. The prevalence of bulges, but not of protrusions, increased with age. The most common nonintervertebral disk abnormalities were Schmorl’s nodes (herniation of the disk into the vertebral-body end plate), found in 19 percent of the subjects; annular defects (disruption of the outer fibrous ring of the disk), in 14 percent; and facet arthropathy (degenerative disease of the posterior articular processes of the vertebrae), in 8 percent.. The findings were similar in men and women. The authors concluded that on MRI examination of the lumbar spine, many people without back pain have disk bulges or protrusions but not extrusions. The authors went further to state that given the high prevalence of these findings and of back pain, the discovery by MRI of bulges or protrusions in people with low back pain may frequently be coincidental. In another study [4] [3], which tracked the natural history of individuals with asymptomatic disc abnormalities in magnetic resonance imaging the authors stated that the high rate of lumbar disc alterations recently detected in asymptomatic individuals by magnetic resonance imaging demands reconsideration of a pathomorphology-based explanation of low back pain and sciatica.

The origins of pain are the biochemical mediators of inflammation and the inflammatory response. To treat pain, we must block these mediators and block the signals they send up through the nerve cells. We can now measure many of these inflammatory mediators in the blood and spinal fluid. However, our current technology does not allow us to image these mediators. Hopefully sometime in the future we will be able to do so.

Inflammation occurs when there is infection or tissue injury. Tissue injury may arise from a physical, chemical or biological trauma or irritation. Degeneration of tissue subsequent to aging or previous injury can also lead to inflammation. Injured tissues can be muscle, ligament, disks, joints or nerves. A variety of mediators are generated by tissue injury and inflammation. These include substances produced by damaged tissue, substances of vascular origin as well as substances released by nerve fibers themselves, sympathetic fibers and various immune cells [5] [4]. There are three phases of an inflammatory response: initiation, maintenance and termination. Upon tissue injury or painful stimulation, specialized blood cells in the area such as basophils, mast cells and platelets release inflammatory mediators serotonin, histamine and nitric oxide. Subsequent to the binding of serotonin to its receptor, there is inflammation of the adjacent nerves and the nerve endings release short-lived inflammatory peptide proteins such as substance P, Calcitonin gene-related peptide (CGRP). In addition, clotting factors in the blood produce and activate potent inflammatory mediator peptide proteins called neurokinin A, bradykinin, kallidin and T-kinin. All of these proteins increase blood flow to the area of injury, stimulate arachidonic acid metabolism to generate inflammatory mediators prostaglandins and attract specialized immune cells to the area. The first immune cells to the area are neutrophils then monocytes and macrophages. These are the same cells that provide the body’s front line defense against bacterial infection. These immune cells release powerful enzymes that can digest any bacteria that have invaded the site of injury. The cells also release potent inflammatory chemical mediators (called cytokines) to attract and activate other cells of the immune system. Shortly thereafter the area of bacterial invasion or tissue injury is invaded by the other immune cells, which include white blood cells such as T helper cells, lymphocytes, neutrophils, eosinophils, and other cells such as fibroblasts and endothelial cells. These immune cells respond to the chemical mediators, release destructive enzymes to kill any invading organism and release more chemical mediators to attract more immune cells. A consequence of this immune response is tissue damage, pain and spasm. In a sense the initial immune reaction ignites a cascade of immune reactions and generates an inflammatory soup of chemical mediators. These chemical mediators produced by the immune cells include prostaglandin, nitric oxide, tumor necrosis factor alpha, interleukin 1-alpha, interleukin 1-beta, interleukin-4, Interleukin-6 and interleukin-8, histamine, serotonin, In the area of injury and subsequently in the spinal cord, enzymes such as cyclooxygenase increase the production of these inflammatory mediators. These chemical mediators attract tissue macrophages and white blood cells to localize in an area to engulf (phagocytize) and destroy foreign substances.

Molecules called selectins cause the circulating immune leukocytes to slow their flow and roll along the inner blood vessel wall [6] . Inflammatory mediators such as Il-1 and TNF-alpha produced by cells at the injured or infected site then stimulate the endothelial cells that form blood vessels to produce other chemical mediators such as interleukin-8 (IL-8). The mediators are held on the inner surface of the endothelial cells where they interact with receptors on the surface of the rolling leukocytes. This interaction, in turn, triggers the activation of molecules called integrin on the surface of the leukocytes. Activation of these integrins by inflammatory mediators enables the slowly rolling leukocytes to strongly bind to adhesion molecules such as ICAMs (intercellular adhesion molecules) and VCAMs (vascular cell adhesion molecules) on the inner surface of the vascular endothelial cells. Macrophage-produced mediators such as Interleukin-1 and TNF-alpha stimulate the production of these adhesion molecules on the vascular endothelium. Once bound to the endothelial cells, the leukocytes then flatten and squeeze between the endothelial cells to leave the blood vessels and enter the tissue. The leukocytes are then chemically attracted to the injured site by the inflammatory mediators. The chemical mediators released during the inflammatory response give rise to the typical findings associated with inflammation