What is Central Sensitization? | El Paso, TX Chiropractor

Central sensitization is a state of the nervous system that’s related to the development and maintenance of chronic pain. When central sensitization occurs, the nervous system undergoes a process known as wind-up, becoming regulated in a state of constant increased reactivity. This persistent, or regulated, state of reactivity decreases the threshold for what causes pain and subsequently learns to the persistence of pain after the initial injury has healed. Central sensitization has two major characteristics. Both have an increased sensitivity to pain and to the feeling of touch. These are referred to as allodynia and hyperalgesia.

Allodynia occurs when an individual experiences pain in circumstances that are not supposed to be painful. For instance, chronic pain patients often experience pain even with things as simple as touch or a massage. In these situations, nerves in the region that has been touched send signals through the nervous system into the brain. Because the nervous system is in a constant state of heightened reactivity, the brain fails to generate a mild feeling of touch as it should, given that the stimulus that initiated it was a gentle touch or massage. Instead, the brain produces a sense of pain and discomfort.

Hyperalgesia occurs when a stimulus that’s usually considered to be somewhat painful is perceived as a much more debilitating pain than it ought to be. For instance, chronic pain patients who experience a simple bump, which generally would be mildly painful, will often feel intense pain. Again, once the nervous system is in a state of high reactivity, it amplifies pain.

Peripheral and Central Sensitization

Chronic pain patients sometimes believe they might be suffering from a mental health issue because they understand from common sense that touch or simple bumps produce tremendous amounts of pain or discomfort. Other times, it’s not the patients themselves who feel this way, but their friends and family members. Individuals who don’t suffer from chronic pain may witness others who have central sensitization experience pain at the slightest touch or cry out at the simplest bump. However, because they don’t have the condition, it may be difficult for them to understand what someone who does is going through.

In addition to allodynia and hyperalgesia, central sensitization exhibits other well-known features, although they may occur less frequently. Central sensitization may lead to heightened sensitivities across all senses, not just the sense of touch. Chronic pain patients can sometimes report sensitivities to light, smell, and sound. As such, regular levels of light may seem overly bright, or even the perfume aisle in the department store can produce a headache. Central sensitization can also be associated with cognitive deficits, including poor concentration and impaired or short-term memory. Central sensitization also interferes with increased levels of psychological distress, particularly fear and anxiety. After all, the nervous system is responsible not merely for senses, like pain, but also for emotions. If the nervous system is constantly in a state of reactivity, patients will likely experience nervousness or anxiety. Lastly, central sensitization is also correlated with sick role behaviors, including restlessness and malaise, as well as pain behaviors.

Central sensitization has long been known as a potential consequence of stroke and spinal cord injury. However, it is increasingly believed that it plays a part in several different chronic pain disorders. It may happen with chronic low back pain, chronic neck pain, whiplash injuries, chronic tension headaches, migraine headaches, rheumatoid arthritis, osteoarthritis of the knee, endometriosis, injuries sustained in an automobile accident, and even following surgeries. Fibromyalgia, irritable bowel syndrome, and chronic fatigue syndrome all appear to occur due to central sensitization as well.

Central Sensitization and C Fibers

What Causes Central Sensitization?

Central sensitization involves specific changes to the nervous system. Changes occur in the dorsal horn of the spinal cord and in the brain, particularly at the cellular level, such as at receptor sites. As mentioned previously, it has long been proven that fractures and spinal cord injuries can cause central sensitization. It stands to reason. Strokes and spinal cord injuries cause harm to the central nervous system, including the brain in the case of strokes and the spinal cord in the case of spinal cord injuries. These injuries change the sections of the nervous system that are involved in central sensitization.

However, what about the other, more prevalent, types of chronic pain disorders, recorded above, such as headaches, chronic back pain, or pain in the extremities? The accidents or conditions that lead to these kinds of chronic pain are not direct injuries to the brain or spinal cord. Rather, they include injuries or conditions that affect the peripheral nervous system, particularly in those areas of the nervous system that involve the spinal cord and brain. How can health issues associated with the peripheral nervous system contribute to modifications in the central nervous system and cause chronic pain in the isolated area of the initial injury? In summary, how can isolated migraine headaches eventually become chronic daily headaches? How can an acute low back lifting injury become chronic low back pain? How does an injury to the hand or foot turn into a complex regional pain syndrome?

There are probably multiple factors that cause the development of central sensitization in these ‘peripheral’ chronic pain disorders. These variables may be divided into two classes:

• Factors that are associated with the state of the central nervous system before the onset of the initial pain or injury condition
• Factors that are associated with the central nervous system following the onset of the initial pain or injury condition

The first group involves factors that may predispose individuals to developing central sensitization following an accident, and the next group involves antecedent factors that exacerbate central sensitization once pain begins.

Dr. Alex Jimenez’s Insight

Chronic pain can often modify the way the central nervous system itself functions, so much so that a patient may become more sensitive to pain with less provocation. This is what’s referred to as central sensitization and it generally involves changes in the central nervous system, or CNS, more specifically, in the brain and the spinal cord. Central sensitization has been associated with several common diseases and it’s even been reported to develop with something as simple as a muscle ache. Central sensitization has also been documented to persist and worsen even in the absence of obvious provocation. Several factors have also been attributed with the development of central sensitization, although the true cause is still unknown.

Predisposing Factors for Central Sensitization

There are likely biological, emotional, and environmental predisposing factors that contribute to central sensitization. Low and high sensitivity to pain, or pain thresholds, can be attributed in part to numerous genetic factors. While there’s currently no research to support a causal relationship between preexisting pain thresholds and the development of central sensitization after an incident, it’s largely assumed that such a relationship will eventually be found.

Psychophysiological factors, such as the stress response, are also likely to play a role in the development of central sensitization. Direct experimental evidence from animals and humans, as well as prospective studies on humans, has demonstrated a connection between stress and a decrease in pain thresholds. Similarly, different preexisting anxiety about pain is consistently related to higher pain sensitivities. All these psychophysiological aspects suggest that the preexisting state of the nervous system is also a significant determinant of central sensitization following the onset of pain. If the stress response has made the nervous system responsive before injury, then the nervous system may be more prone to becoming sensitized once pain onset occurs.

There is also considerable indirect evidence to support this theory. A prior history of anxiety, physical and psychological trauma, and depression is predictive of the onset of chronic pain later in life. The most common denominator between chronic pain, anxiety, nervousness, injury, and depression is the nervous system. They’re all states of the nervous system, especially a persistently changed, or dysregulated, nervous system.

It’s not the preexisting health issues that make individuals more vulnerable to injury or the onset of illness, as injury or disease is apt to happen on a somewhat random basis across the populace. Instead, preexisting health issues are more inclined to make people prone to the development of chronic pain once an injury or disease occurs. The dysregulated nervous system, at the time of injury, for instance, may interfere with the normal healing trajectory and thereby prevent pain from subsiding once tissue damage is healed.

Factors Resulting in Central Sensitization After Onset of Pain

Predisposing factors may also contribute to the development of central sensitization. The onset of pain is frequently associated with subsequent development of conditions, such as depression, fear-avoidance, nervousness or anxiety, and other phobias. The stress of those responses can, in turn, further exacerbate the nervous system’s reactivity, leading to central sensitization. Inadequate sleep is also a frequent effect of living with chronic pain. It is also associated with increased sensitivity to pain. In what’s technically known as operant learning, interpersonal and environmental reinforcements have long been proven to lead to pain behaviors; however, it is also evident that such reinforcements may lead to the development of central sensitization.

Treatments of Central Sensitization

Treatments for chronic pain syndromes that involve fundamental sensitization typically target the central nervous system or the inflammation that corresponds with central sensitization. All these often generally include antidepressants and anticonvulsant medications, and cognitive behavioral treatment. While typically not considered to target the central nervous system, regular mild aerobic exercise alters structures in the central nervous system and contributes to reductions in the pain of many ailments that are mediated by central sensitization. As such, moderate aerobic exercise is used to treat chronic pain syndromes marked by central sensitization. Non-steroidal anti-inflammatory drugs are used for the inflammation associated with central sensitization.

Finally, chronic pain rehabilitation programs are a standard, interdisciplinary treatment that employs each of the above-noted therapy strategies in a coordinated manner. They also leverage research on the role of operant learning in central sensitization and have developed behavioral interventions to alleviate the pain and discomfort associated with the health issue. Such applications are typically considered the most effective treatment option for chronic pain syndromes. The scope of our information is limited to chiropractic as well as to spinal injuries and conditions. To discuss the subject matter, please feel free to ask Dr. Jimenez or contact us at 915-850-0900.

Curated by Dr. Alex Jimenez

Additional Topics: Sciatica

Sciatica is medically referred to as a collection of symptoms, rather than a single injury and/or condition. Symptoms of sciatic nerve pain, or sciatica, can vary in frequency and intensity; however, it is most commonly described as a sudden, sharp (knife-like) or electrical pain that radiates from the lower back down the buttocks, hips, thighs, and legs into the foot. Other symptoms of sciatica may include tingling or burning sensations, numbness, and weakness along the length of the sciatic nerve. Sciatica most commonly affects individuals between the ages of 30 and 50. It may often develop as a result of the degeneration of the spine due to aging; however, the compression and irritation of the sciatic nerve caused by a bulging or herniated disc, among other spinal health issues, may also contribute to sciatic nerve pain.