subject: Chronic Pain Causes Theories And Effects In Cognition [print this page] Chronic pain was originally defined as pain that has lasted 6 months or longer. It is now defined as pain that persists longer than the normal course of time associated with a particular type of injury. This constant or intermittent pain has often outlived its purpose, as it does not help the body to prevent injury.
Causes
Chronic pain is essentially caused by the bombardment of the central nervous system (CNS) with nociceptive impulses, which causes changes in the neural response. The pain subsequently provokes changes in the behavior of the patient, and the development of fear-avoidance strategies. As a result, the patient may also become physically atrophied and deconditioned. However, it is important to remember that chronic pain is multifactorial, with the underlying biological changes affecting physical and psychosocial factors.
Pain is usually elicited by the activation of specific nociceptors ('nociceptive pain'). However, it may also result from injury to sensory fibres, or from damage to the CNS itself ('neuropathic pain'). Although acute and subchronic, nociceptive pain fulfils a warning role, chronic and/or severe nociceptive and neuropathic pain is maladaptive.
Types
It discusses chronic pain in two categories: malignant and non-malignant.
Pain associated with malignancy can be caused by the cancer itself or by treatment.
Non-malignant pain includes a variety of causes: arthritis, neuropathy/neuralgia, back pain from injury or disorders (cervical stenosis, degenerative disc disease, other disc disorders, etc), migraines and other types of headaches, abdominal pain from chronic pancreatitis, bowel disorders, etc; pelvic pain from various conditions (endometriosis, interstitial cystitis, etc); and also diffuse conditions such as fibromyalgia, reflex sympathetic dystrophy, lupus and other systemic autoimmune/connective tissue conditions, multiple sclerosis and some other neuromuscular conditions.
Chronic pain can occur anywhere in the body; this list includes only a few examples of conditions that can cause chronic pain.
The most common symptoms are a tingling sensation near or around the area where the operation was performed, sharp shooting pains, severe aches after much movement, constant 'low ache' all day and sometimes a general 'weak' feeling.
Contrary to popular belief, all pain is real. This may seem like an obvious statement, but people with chronic pain are sometimes treated as if their chronic pain is either imaginary or exaggerated. In some cases, they feel like they have to prove their chronic pain to their friends, family and doctors. Some patients are told by their doctor that there is no reason for the chronic pain and therefore it cannot be that bad.
Chronic pain is a personal experience and cannot be measured like other problems in medicine, such as a broken leg or an infection. For instance, a broken leg can be confirmed by an X-ray and an infection by a blood test measuring white blood cell count. Unfortunately, there is no medical test to measure chronic pain levels.
To make matters more challenging for the patient, for many chronic pain problems there is no objective evidence or physical findings to explain the pain. Thus, many chronic pain sufferers go from one doctor to the next searching for explanations. This process can lead to unnecessary evaluations and treatments, in addition to putting the patient at risk for actually being harmed or made worse by the healthcare profession.
Everyone experiences and expresses pain differently. Two people with the exact same injury will feel and show their pain in unique ways depending on a number of things such as:
The situation in which the pain occurs
Thoughts about the chronic pain, such as this is nothing serious versus this pain could kill me
Emotions associated with the chronic pain, such as depression and anxiety versus hopefulness and optimism
Cultural influences determining whether a person is to be more stoic or more dramatic in showing pain to others
The newest theories of chronic pain can now explain, on a physiological level, how and why people experience pain differently.
Modern theories of chronic pain
The specificity theory of pain
In the 16th century, the French philosopher and mathematician Rene Descartes proposed one of the original theories of pain. His theory proposed
This theory - the specificity theory - is generally accurate when applied to certain types of injuries and the acute pain associated with them.
Problems with specificity theory of pain
Various clinical observations have proven the specificity theory to be inadequate to explain chronic pain. Dr. Henry Beecher, who worked with severely wounded soldiers during World War II, was one of the first doctors to question the theory. He observed that only one out of five soldiers carried into a combat hospital complained of enough pain to require morphine. These soldiers were not in a state of shock, nor were they unable to feel painindeed, they complained when the IV lines were placed. They found that severity of wound was not related to the intensity of pain. Also he found that the pain depends upon the meaning attached to the injury. It was found that the civilian with the same amount of injury as the soldier in war was having, the civilian required more morphiene. Also ,how hypnosis can be used as anesthesia is not been explained by this theory .
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Modern Ideas: The Gate Control Theory of chronic pain
Due to the observations that raised questions, a new theory of pain was developed in the early 1960s to account for the clinically recognized importance of the mind and brain in pain perception. It is called the gate control theory of pain, and it was initially developed by Ronald Melzack and Patrick Wall.
Although the theory accounts for phenomena that are primarily mental in nature - that is, pain itself as well as some of the psychological factors influencing it - its scientific beauty is that it provides a physiological basis for the complex phenomenon of pain. It does this by investigating the complex structure of the nervous system, which is comprised of the following two major divisions:
Central nervous system (the spinal cord and the brain)
Peripheral nervous system (nerves outside of the brain and spinal cord, including branching nerves in the torso and extremities, as well as nerves in the lumbar spine region)
Gates open or closed depending upon the number of factors
In the gate control theory, before they can reach the brain these pain messages encounter nerve gates in the spinal cord that open or close depending upon a number of factors (possibly including instructions coming down from the brain). When the gates are opening, pain messages get through more or less easily and pain can be intense. When the gates close, pain messages are prevented from reaching the brain and may not even be experienced.
Although no one yet understands the details of this process or how to control it, the following concepts are presented to help explain why various treatments are effective and how to find solutions to chronic back pain.
Sensory nerves bring information about pain, heat, cold and other sensory phenomena to the spinal cord from various parts of the body. At least two types of nerve fibers are thought to carry the majority of pain messages to the spinal cord:
A-delta nerve fibers, which carry electrical messages to the spinal cord at approximately 40 mph (first or fast pain).
C-fibers, which carry electrical messages at approximately 3 mph to the spinal cord (slow or continuous pain)
A good example of how these respective nerve fibers work is the activation of the A-delta nerve fibers followed by the activation of the slower C-fibers. The activation of other types of nerve fibers can modify or block the sensation of pain.
Sensory nerve fibres faster than A- delta fibres prevents pain
After hitting ones elbow or head, rubbing the area seems to provide some relief. This activates other sensory nerve fibers that are even faster than A-delta fibers, and these fibers send information about pressure and touch that reach the spinal cord and brain to override some of the pain messages carried by the A-delta and C-fibers.
The action of these other types of nerve fibers helps to explain why treatments such as massage, heat or cold packs, transcutaneous nerve stimulation, or even acupuncture are often effective in treating back pain..
Factors determining how the spinal nerve gates will manage pain
Many factors determine how the spinal nerve gates will manage the pain signal. These factors include the intensity of the pain message, competition from other incoming nerve messages (such as touch, vibration, heat, etc), and signals from the brain telling the spinal cord to increase or decrease the priority of the pain signal. Depending on how the gate processes the signal, the message can be handled in any of the following ways:
Allowed to pass directly to the brain
Altered prior to being forwarded to the brain (for instance, influenced by expectations)
Prevented from reaching the brain (for instance, by hypnosis-induced anesthesia)
Once a pain signal reaches the brain, a number of things can happen. Certain parts of the brain stem (which connects the brain to the spinal cord) can inhibit or muffle incoming pain signals by the production of endorphins, which are morphine-like substances that occur naturally in the human body. Stress, excitement, and vigorous exercise are among the factors that may stimulate the production of endorphins. The impact of endorphins is why athletes may not notice the pain of a fairly serious injury until the big game is over. It is also why regular low-impact aerobic exercise (e.g. a riding stationary bike) can be an excellent method to help control chronic back pain.
Pain messages may also be directed along a variety of pathways in the brain.
For instance, a fast pain message (A-delta fiber) is relayed by the spinal cord to specific locations in the brain, namely the thalamus and cerebral cortex. The cortex is the portion of the brain where higher thinking takes place. A fast pain message reaches the cortex quickly and prompts immediate action to reduce the pain or threat of injury.
In contrast, chronic pain tends to move along a slow pathway (C-fiber). Slow pain tends to be perceived as dull, aching, burning, and cramping. Initially, the slow pain messages travel along the same pathways as the fast pain signals through the spinal cord. Once they reach the brain, however, the slow pain messages take a pathway to the hypothalamus and limbic system. The hypothalamus is responsible for the release of certain stress hormones in the body, while the limbic system is responsible for processing emotions. This is one reason why chronic back pain is often associated with stress, depression, and anxiety. The slow pain signals are actually passing through brain areas that control these experiences and emotions.
The brain also controls pain messages by attaching meaning to the personal and social context in which the pain is experienced. This occurs in the cortex. As we have seen previously, soldiers who are wounded in combat may display much less pain than similarly wounded civilians involved in accidents. The meaning attached to the situation seems to be the important difference.
Opening and closing the pain gates for chronic pain
. The brain can send signals down the spinal cord to open and close the nerve gates.
In times of anxiety or stress, descending messages from the brain may actually amplify the pain signal at the nerve gate as it moves up the spinal cord. Alternatively, impulses from the brain can close the nerve gate, preventing the pain signal from reaching the brain and being experienced as pain.
The events and conditions that may open the pain gates and cause more suffering include:
Sensory factors, such as injury, inactivity, long-term narcotic use, poor body mechanics, and poor pacing of activities
Cognitive factors, such as focusing on the chronic pain, having no outside interests or distractions, worrying about the pain, and other negative thoughts
Emotional factors, such as depression, anger, anxiety, stress, frustration, hopelessness, and helplessness.
Alternatively, influences that can close the pain gates and reduce suffering include:
Sensory factors, such as increasing activities, short-term use of pain medication, relaxation training and meditation.
Cognitive factors, including outside interests, thoughts that help the patient cope with the pain, and distracting oneself from the chronic pain.
Emotional factors, such as having a positive attitude, overcoming depression, feeling reassured that the pain is not harmful, taking control of ones chronic pain and life, and stress management
Chronic pain is a subjective experience and has not only physical, but also psychological and social dimensions Among the different factors relevant to the psychological assessment and treatment of chronic pain, those of a cognitive nature play a prominent role, due in large part to the fact that pain is a perceptual phenomenon. Indeed, cognitive factors are largely responsible for the final (cortical) part of the perception process, so that, without subtracting importance from the more sensorial and even emotional aspects of pain, the final integrating point is cognitive in character.
Of the different cognitive variables that can mediate in the experience of pain, few variables are selected that have greatest relevance to chronic pain.
Pain prevalence and impaired cognition:
Pain prevalence did not differ between the communicative resident with normal cognition (48.7%), mildly impaired cognition (46.5%), or severely impaired cognition (42.9%). However, the latter 2 groups reported more acute pain than those with normal cognition (7.9% to 14.1% vs. 2.5%). Those with impaired cognition reported constant pain more often, reported fewer total sites of pain, and had more frequent and more severe pain. Regardless of cognitive status, 73.3% to 100% of residents had significant scores on depression or anxiety measures when they reported pain-related mood disturbance. Pain-related reduction in activity was associated with a lower Human Activities Profile score. Sixteen of 36 uncommunicative residents had pain on the Pain Assessment in Advanced Dementia and at least 12 of them had significant mood disturbance. They found that Cognitive status does not affect pain prevalence; however, it affects the chronicity and characteristics of reported pain. Self-report of pain-related mood involvement is associated with significant mood scores.( Leong and Nuo ,2007)
Older adults with chronic low back pain demonstrated impaired neuropsycholgical performance as compared with pain-free older adults. Further, pain severity was inversely correlated with Neuropsycholgical performance, and Neuropsychological performance mediated the relationship between pain and physical performance ( Weiner et al.,2006).
In a subset of chronic pain disorder patients there were disturbances of mood , sleep, energy, libido, memory/concentration, behaviour and stress tolerance.( Rome and Rome , 2000)
Cancer pain and cognitive functions:
Cancer survivors did not differ from persons without cancer on the cognitive functions.( Keating et al., 2005).
Chronic pain in rats impaired spatial learning and memory function
Chronic pain stress induced by CFA impairs the spatial learning and memory function in neonatal rats. These effects might exert through down-regulating Bcl-2 and BDNF mRNA expression in the hippocampus (Li et al , 2005)
Causal attributions and beliefs about pain
Causal attributions and beliefs that the pain is caused by external factors like luck or organic causes increases the perception of pain ( Demjen and Bakel, 1981; ). The patients who believed that pain is a mysterious phenomenon apart from poor adherence of treatment also presented low self esteem and high level of somatization( Williams and Thorn, 1989). Also they used lower coping strategies
( Williams and Keefe, 1991)
Locus of control and pain
High internal locus of control present active coping strategies with regard to their pain (Brown and Nicassio, 1987; Crisson and Keefe, 1988) while patients with strong beliefs in the luck presented higher level of psychological unease, feel more helplessness and tend to use more passive strategies with pain ( Crisson and Keefe.,1988).
Impaired attention and pain
Glass (2006) found that fibromyalgia patients have impaired control of attention, due to chronic pain. Neuroimaging studies demonstrated cerebral abnormalitites and pattern of increases neural recruitment during cognitive tasks. Some chronic pain patients did show scores suggestive of attentional impairment( Etherton et al 2006). There is a poor attention to chronic pain due to osteoarthritis in community-dwelling elders with cognitive impairment.( Cornali et al, 2006)
Chronic non-malignant pain patients (N=91) treated in a multidisciplinary pain centre were compared with age and sex matched healthy volunteers (N=64).It was found that Continous reaction time and Finger tapping test were impaired in the total patient sample. Treatment with opioids was associated with poorer performance of paced auditory serial addition task. ( Sijogren et al 2005). Dick et al (2002) found that the patients with fibromyalgia, rheumatoid arthritis and musculoskeletal pain patients have impaired cognitive functioning on the test sensitive to attention.
Decrease in attention in the rats with colotis( chronic visceral inflammatory state of pain).
In a study colitis was induced in rats by an emema containing 2,4,6 trinitorbenzen sulfunic acid and it was found that rats with colitis had decreased attention level but there was no change in their locomotor activity and interest in the environment on memory encoding. ( Mellicamps et al, 2004)
Slow information processing and pain
Patients with chronic fatigue syndrome have slow information processing as found in the study by Glass (2006). The results of a study highlighted (Moseley et al , 2005)that the differences between acute and chronic pain and may reflect a bias in information processing in acute pain toward the affected part. Both pain and the expectation of pain increased response time to recognize the opposite hand. The findings are consistent with a bias in information processing toward the painful or impending painful hand.( Hudson et al, 2006).
In a study, it was found that diagnosed chronic pain patients demonstrated a recall bias away from depression related stimuli while the non diagnosed chronic patients did not. The diagnosed ankylosing spondylitis also showed a bias
