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Chronic Pain

Dernière mise à jour : 14 mai 2020



The International Association for the Study of Pain defines pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage”. Each person's perception of pain can be intensified or diminished by outside factors including anticipation, stress, mood, cognition, beliefs and genetics.

Pain can be divided into two main categories, acute or chronic, based on certain characteristics (table 1).

  1. Acute pain is a normal biologically important protective function that warns us against danger and injury. It’s onset is usually sudden resulting from a specific injury or illness, it is generally short-lived, not lasting longer than 6 weeks, and once resolved patients are able to resume a normal lifestyle.

  2. Chronic Pain (CP) is a recurrent or ongoing pain lasting longer than three months and in some cases years. This multifaceted disorder lasts long after the initial trigger has disappeared and in some cases there is no apparent past injury or illness. The World Health Organization estimates that approximately 22% of primary care patients worldwide suffer from CP and Canadian statistics report that 19% of the Canadian population (about 6 million people) are living with CP.

If not adequately treated, CP can have a significant negative impact on both physical and emotional aspects of life; In fact, more than three quarters of sufferers report poor concentration, lack of energy, inability to enjoy life, and feelings of depression resulting in reduced productivity.


Our ability to feel pain is because peripheral sensory neurons, the noniceptors which are present in almost all parts of our bodies, are activated by stimuli which cause or threaten to cause damage to the body. These chemical, mechanical or thermal stimuli are responsible for the cascade of physiological responses which translate into the sensation of pain.

When nociceptors are exposed to noxious stimuli they send nervous signals up the peripheral nerve to the spinal cord triggering the release of neurotransmitters within the spinal cord which in turn activate other nerves that transmit the signal to the brain. In the brain the thalamus relays the signals to the somatosensory cortex, frontal cortex and limbic system.

Example: you stub your toe and immediately feel a sharp pain at the site of the injury. This is accompanied by inflammation, swelling and redness which are all part of the body’s natural response mechanisms. The damaged tissues release inflammatory mediators which activate the nociceptors and initiate the healing process.


Immediately at the site of injury the acute and sharp pain is often accompanied by Inflammation, swelling, redness and the activation of the body’s natural response mechanisms. The damaged tissues release inflammatory mediators including bradykinin, serotonin, cytokines and prostaglandins which activate the nociceptors and participate in the healing process.

The activated nociceptors transform the pain stimuli into electrical signals through the exchange of sodium and potassium ions, occurring at the cell membranes, creating depolarisation and repolarization reactions. These electrical signals are conducted to the spinal cord and the central nervous system. A large brain network is activated during pain with the commonest areas being the primary and secondary somatosensory (S1 and S2), insular, anterior and cingulate cortex and prefrontal cortex, and the thalamus


Nerves are composed of thousands of axons (hair-like filaments) classified according to their diameter, the presence or absence of a fatty myelin coating, and to the type of receptor they connect to. Myelin is a protective insulating material implicated in the nourishment of the axons and the speed of transmission of the electric impulses. Two main types of afferent nerve fibers are involved in pain transmission, they are the A fibres (which include A-beta and A-delta fibres) and C fibers. The larger axons belong to the A fibre group and are heavily myelinated. The unmyelinated pain fibres belong to the C fiber group (Table 2).

The network of nerves covering the body is composed of different types of nerve endings each programmed to respond to specific stimuli and requiring specific minimum intensities of stimulation before they are triggered to respond.


1. Transduction: nociceptors, free nerve endings, of C fibres and A-delta fibers of afferent neurons respond to noxious stimuli

2. Transmission: pain impulses are transmitted from site of transduction along the nociceptor fibers to the dorsal horn in the spinal cord then to the brain stem and thalamus, then to multiple areas in the brain where they are processed

3. Modulation: is the suppression or intensification of pain impulses in the spinal cord by endogenous or exogenous factors. Endogenous opioids, present throughout the CNS are involved in inhibiting the transmission of pain impulses

4. Perception: noxious stimuli transmitted to the brain result in neuronal activity resulting in the perception of pain


The main types of pathways leading to CP identified are:

  1. Nociceptive Pain: normal, acute, localised response to threats in the environment manifesting as a high pain threshold resulting from damage to somatic or visceral tissue from noxious stimuli such as severe trauma or burns or post-operative pain.

  2. Inflammatory Pain: low threshold pain resulting from several conditions, including rheumatoid arthritis (RA), osteoarthritis (OA), gout, and ankle sprains…

  3. Neuropathic Pain: low threshold, radiating pain manifesting as electric, stabbing, burning, or tingling sensations caused by neuronal damage. Causes include diabetic neuropathies, post-herpetic neuralgias, alcoholism, exposure to toxins, chemotherapies, traumas.

  4. Sensory Hypersensitivity or Central Pain: low threshold pain not related to any known inflammation, neuronal damage or noxious stimuli. It is hypothesized to be the result of persistent neuronal dysregulation, such as in the case of fibromyalgia, migraine, irritable bowel syndrome, and non-cardiac chest pain.


The different treatment options available are not suitable for all patients, the therapeutic choice depends on several factors including: the characteristics of the pain (cause, location, intensity, frequency, duration), the patient’s general condition and psychological status, prescription medications currently being used, and the presence or absence of other pre-existing medical conditions.

1. Oral Medications

  • Over the Counter Non-Steroidal Anti-Inflammatory Drugs (NSAIDs): including aspirin, ibuprofen, and acetaminophen, muscle relaxants

  • Prescription Opioids: methadone, oxycodone, Hydrocodone, which help reduce pain signals.

  • Other Medications: anti-seizure medications (particularly for neuropathic pain), antidepressants (particularly tricyclics) , and muscle relaxants

3. Pain Injections: Injections which deliver medications (steroids or local anesthetics) directly to the painful location. Pain relief may last from a few months to 1 year but is not always guaranteed and sometimes repeat injections may be necessary to achieve results.

  • Nerve Root Blocks, for nerves located along the spine

  • Epidural Steroid Injections, for disc disease such as herniated discs

  • Trigger Point Injections, for muscle knots which can be tight enough to compress nerves

4. Pain Pumps: a reservoir implanted under the skin, between the muscle and the abdomen, with an attached catheter which delivers steroids or local anesthetics directly to the spinal cord receptors, thereby interrupting the transmission of pain signals to the brain. This method delivers an automatic continuous or timed slow drip of medication which may offer effective longer-lasting pain relief and the ability to function and participate in normal daily activities.

5. Radiofrequency Ablation or Neurotomy (RFA): procedure which uses a needle heated up by radio waves. The tip of the needle is introduced very close to the nerve to create a heat lesion which disrupts the nerve’s ability to send pain signals to the brain. This technique is used for many types of pain, including lower back/hip/neck or knee pain, arthritis, and neuropathy


Numerous treatment options for CP available within the complementary and alternative medicine (CAM) approach have been researched. One study, made up of a cohort of 500 subjects suffering from back pain, aiming to identify the benefits of CAM methods (which included herbal therapy, balneotherapy, cupping and massage manipulation) found that most patients using CAM perceived benefits.

It is also important to mention that whenever possible, the treatment of pain should be focused on the cause and not only on diminishing the sensation of pain. Therefore, it is necessary to address nutrition, deficiencies, excesses and toxicities, as well as underlying conditions. Following are different CAM approaches to the treatment of CP.


Acupuncture and cupping are techniques which work to restore a healthy flow of Qi in order to resolve blockages. A German study, published in the Archives of Internal Medicine Sept. 24, 2007 found acupuncture more effective than other physical therapy options for low back pain (LBP). Another clinical trial which took place in China found laser acupuncture plus Chinese cupping at the Weizhong (BL40) and Ashi acupoints effectively reduced pain and inflammation in chronic nonspecific LBP. In a trial, including 100 patients suffering from chronic LBP, patients were randomized to regular pulsatile cupping with 8 treatments plus paracetamol on demand, minimal cupping with 8 treatments plus paracetamol on demand and the control group with paracetamol on demand only. Pain intensity and back function were evaluated at the end of 4 and 12 weeks. In conclusion, both forms of cupping were effective in controlling LBP at 4 weeks, only pulsatile cupping showed effects compared to control after 12 weeks.


The use of therapeutic doses of vitamins, minerals and other nutrients to alleviate CP has been studied extensively. Some of the most popular ones being omega-3 fatty acids for their anti-inflammatory properties, MSM/chondroitin/glucosamine and collagen to help rebuild cartilage and collagen, and magnesium as a muscle relaxant. Calcium, potassium, B vitamins are also contenders.

One study demonstrated magnesium to enhance opioid-induced analgesia in animal studies in both chronic and acute pain, thus reducing opioid consumption and potential opioid side effects. Certain B vitamins (B1, B6, B12) in large doses inhibited nociceptive activity in the brain and spinal cord.

L-tryptophan, a precursor to serotonin, appears to reduce the sensitivity to pain. One study on 96 patients suffering from maxillofacial pain found improvement in most patients within 2 weeks of taking a dose of 50mg/Kg body weight of tryptophan.

D-Phenylalanine inhibits the degradation of the endogenous opioids enkephalins and therefore may have an analgesic effect. 250 mg of D-phenylalanine administered 3 to 4 times per day have been used to decrease the pain of osteoarthritis.


Numerous trials have found homeopathic compound treatments to be very effective for the treatment of rheumatoid arthritis, migraine, fibromyalgia, neuralgia, chronic lower back pain as well as many other types of pain. Many of the trials were double-blind and placebo controlled. Individual remedies are also effective in reducing pain.

One double-blind randomized placebo-controlled trial which took place in Germany with 228 participants and which lasted four years found the homeopathic drug combination Lymphdiaral Basistropfein can improve the treatment of lower back pain.


Botanical medicine has much to offer for pain relief since many plant constituents have actions similar to allopathic treatments, such as anti-inflammatory and muscle relaxant properties. Plants may be administered orally (as single plants or in formulas) or applied topically. They have been used with success for different types of pain, including osteoarthritis (OA), rheumatoid arthritis (RA), lower back pain (LBP), athletic injuries (AI). Table 3 offers a short summary of some botanicals used for CP.

One example of topical phytotherapy involves the use of Cabbage Leaf Wraps (CLW): a study including 81 patients suffering from osteoarthritis of the knee at stages II to III, that lasted 4 weeks, randomly assigned participants to CLW, 10 mg diclofenac topical pain gel (TPG) or usual care (UC). Results found CLW to be more effective than UC but less than TPG for the relief of OA knee pain.


Water (in the form of compresses, wraps, water jets, baths, cold packs, heat packs, etc.) is used to heat and cool the body with the aim of manipulating circulation, inflammation and pain neurology. One study, lasting four weeks on a group of 20 people suffering from lower back pain undergoing three individual sessions of hydrotherapy treatments each week, demonstrated a reduction in pain levels and an improvement in thoraco-lumbar mobility.


  • Spinal adjustment: chiropractic manipulation of vertebrae or painful joints helps restore proper alignment which reduces mechanical stressors causing pain

  • Osteopathy: deep soft tissue manipulations which realign and restore joints, ribs and vertebrae to relieve mechanical stressors causing pain

  • Massage: kneading and massaging of painful areas improves circulation, relieves stress and relaxes tight muscle fibers, thus reducing tension and pain

  • Yoga, Pilates, Tai Qi or Qigong: exercise techniques which involve deep breathing coupled with slow precise movements that improve circulation, increase relaxation and stretch muscles gently


  • Meditation & Relaxation Techniques: aid in releasing tensions in the body, relaxing tight muscles and encourage the production of endogenous opioids

  • Biofeedback: creates awareness of body processes such as muscle tightening and spasms and helps mind to consciously control them

  • Hypnosis: helps reduce stressful emotions and refocuses attention away from pain sensations


Chronic Pain is a condition which affects millions of people worldwide which if not adequately treated can have significant negative impacts on both the physical and emotional aspects of life. CP must therefore be addressed by treating the cause of the pain and not only the symptom.

While pharmaceutical drugs have an important role to play in the management of CP to reduce pain and improve quality of life, they are not the only effective treatments available to patients. CAM therapies must also be seriously considered because of their efficacy, safety and the lack of serious undesirable side effects. They can be used in conjunction with conventional drugs to reduce dosing and toxicity of prescription drugs or they may be used alone in certain cases.


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