Pain is one of the most frequent reasons for which people seek clinical care, yet the specialty of pain medicine and our understanding of pain mechanisms remains in its infancy.
It is well known that there are different pain mechanisms, but this knowledge does not always translate into our approach to pain control. Chronic pain can be defined in biopsychosocial terms and physiologically is multi-mechanistic in nature and requires pain control therapy that addresses each mechanism; it requires a multi-modal approach.
Types of pain
Nociception is one of the more familiar types of pain; it occurs when you stub your toe or burn your hand. Nociceptors on the periphery of the body receive input from noxious stimuli and transmit it via the neural network to the spine and brain; the brain “interprets” the pain messages and causes the body to respond, for example, by removing the hand from a hot object. The pain signals travel along afferent and efferent pain pathways and the neural messages can be amplified or blunted along the way.
Neuropathic pain is more challenging to treat. It can occur when the neural network aberrantly and maladaptively amplifies pain signals from the periphery, which can occur with allodynia. Neuropathic pain may also be present when the neural system sends out pain signals in the absence of clear stimuli, which may occur with painful diabetic peripheral neuropathy or fibromyalgia.
People with chronic pain typically have a neuropathic component to their pain, that is, they may experience both nociceptive and neuropathic pain. Chronic pain is generally defined by duration; typically, it is pain that has persisted for more than three to six months, long after the original injury has healed.
In some cases with chronic pain, the patient does not know what the original cause of the pain was. Chronic pain is a maladaptive form of pain that often presents as diffuse, migratory, intermittent, and may vary in intensity from mild to severe. While chronic pain is often defined in terms of duration, it is fundamentally different from acute pain.
Acute pain is closely associated with an injury or event and follows a somewhat predictable trajectory of lessening in severity as the patient heals. With chronic pain, patients may experience ongoing persistent pain with no clear resolution; patients may suffer chronic pain indefinitely, which may be why it is so closely tied to depression and even suicide.
In addition to nociceptive and neuropathic pain, patients may also experience inflammatory pain. Inflammatory pain is related to the inflammatory process and includes redness, tenderness, warmth and swelling around the affected area. Inflammatory pain is adaptive, but when inflammation becomes chronic (which may happen with patients with osteoarthritis, for example), it can cause persistent pain and contribute to the chronic pain syndrome as a distinct and different pain mechanism.
Acute inflammatory pain may occur with a single noxious event, such as a sprain. The inflammation subsides as the tissue heals. But inflammation can also become chronic inflammatory pain. Osteoarthritis is a good example of this type of condition.
Visceral pain involves the organs deep in the body and often occurs with cancer patients. Visceral pain is often perceived as very severe, hard to pinpoint and may be accompanied by symptoms of nausea, headache or malaise. Sometimes visceral pain can make the patient feel like something is tugging or pulling on an internal organ; cramping may also be reported.
Awareness of pain
People with chronic pain typically experience different types of pain from different mechanisms or multi-mechanistic pain. The patient may be unaware of the different mechanisms at play but, if asked to characterize the pain, the patient may recognize that some of the pain is sharp and easy to localize (nociceptive pain); other pains can be dull, hard to pinpoint, and intermittent (visceral pain), while other pain is more “electrical” and comes on suddenly and then goes away (neuropathic pain). Then there is incident pain with certain types of movement (inflammatory pain in the joints, for instance). Pain control for such patients must address each of the mechanisms in order to be optimally effective.
When assessing a chronic pain patient, it is helpful to begin by asking the patient to identify all of his or her pain sites, starting with the most severe or most disabling. Chronic pain patients may suffer from pain at multiple pain locations and these pains may or may not be related to each other.
Then, working site by site, ask the patient to rate the pain intensity at each site and describe the pain and report if specific things make the pain better or worse. Many patients lack the vocabulary to describe pain well but the clinician may be able to prompt them to determine what types of pain are involved. (See chart.)
Nociceptive pain may respond to chiropractic adjustments, lifestyle changes (exercise, weight loss, etc.), or techniques from complementary and alternative medicine (such as acupuncture and massage). However, in patients with multi-mechanistic pain, neuropathic pain may still persist even if nociceptive pain is controlled.
Treatment of pain
Neuropathic pain may require specific treatment such as exercise or relaxation techniques. Even then, inflammatory pain may still persist and may require special treatment, such as postural changes (leg elevation) or cold therapy to reduce swelling.
It is useful to consider what will not work. If a patient with multi-mechanistic pain comes to the clinic and gets a chiropractic adjustment, this may help his or her nociceptive pain but may not address the neuropathic component of pain. The patient—not differentiating pain mechanisms—may feel that the treatment “did not work.” In actuality, it may have worked very well at what it could do, but it may not have been able to relieve neuropathic pain.
Thus, clinicians should educate patients about multi-mechanistic pain and the need in some cases for multimodal pain therapy. Multi-modal pain therapy may involve: chiropractic care (nociceptive pain), lifestyle modification (nociceptive pain, inflammatory pain), cold or hot therapy (inflammatory pain), exercise (nociceptive and neuropathic pain), cognitive or behavioral therapy (all types of pain), topical therapy (nociceptive and inflammatory pain), and so on. Such patients should be educated that there may be no single thing they can do to eliminate their pain, but rather that they must pursue multiple therapies to address the multiple pain mechanisms involved.
Pain, particularly challenging pain that has persisted over many months, is often multi-mechanistic in nature and requires a multi-modal therapeutic approach. Patients who suffer from multi-mechanistic pain but only receive one type of treatment may be left with unresolved pain and not understand why. While chiropractic care may address much of the pain, clinicians must recognize that different mechanisms may require other treatments in order to provide the patient with maximum pain control.
Joseph V. Pergolizzi, Jr., MD, studies the causes and best treatments for acute and chronic pain. He has published more than 100 peer-reviewed articles in medical journals, has authored book chapters on pain, and speaks extensively on the subject. He is a co-founder of NEMA Research, Inc., in Naples, Fla. His writing and information about his products can be found at healthydirections.com.
Christopher G. Gharibo, MD, is director of pain medicine for the Department of Anesthesiology, Perioperative Care and Pain Medicine at NYU Langone Health in New York, NY.