Central sensitization: causes, and associated symptoms and diseases

Pain is an unpleasant sensory experience that can be experienced by all living beings with a central nervous system.. At an evolutionary and ethological level, in the natural world, pain is self-explanatory: this emotion it keeps us alert and teaches us what we should not approach if we want to survive in the long run term.

In our case, the nociceptors (free nerve endings of primary sensory neurons) are the receptors that mainly respond to noxious stimuli. These send impulses through afferent neurons to the spinal cord, and the spinal cord transmitted to the brain, which interprets the pain signal and causes the body's response relevant.

As counterintuitive as it may sound, without pain there is no life, because without the perception of danger there is no concept of "survival". Can you imagine what life must be like for a human being with modified pain perception? Nor do you have to think too much, because below we will tell you everything about a term widely linked to this idea: core sensitization.

• Related article: "Parts of the Nervous System: functions and anatomical structures"

What is central sensitization?

Central sensitization can be defined in the first instance as a pathological process of the nervous system. which consists of a decrease in the pain threshold, which causes hypersensitivity to noxious stimuli. This event, known as SC by its acronym, is caused by the increase in the excitability of neurons of the central nervous system (CNS) especially in spinal cord neurons of the second order.

In this state of hyperexcitability, the neurons involved are more easily activated by potentially harmful signals and tend to amplify the information received as it is transmitted along the nerve tree. Thus, it gives rise to a series of pathological pictures that we will see below.

When you respond so exaggeratedly to a peripheral stimulus, you experience two specific terms. We tell you briefly.

1. hyperalgesia

Central sensitization cannot be conceived without hyperalgesia, since they are two sides of the same coin. This last term refers to the increased sensitivity to pain and extreme reaction to it by the patient. Something that was already painful before now becomes unbearable.

According to the National Cancer Institute (NIH), hyperalgesia is typical of processes that damage nerves or produce chemical changes in nerve pathways involved in pain perception. Postherpetic neuralgia is a clear example of this, since the place affected by herpes (shingles) can be hypersensitive for 3 months or more after onset, due to damage to nerve fibers superficial.

2. allodynia

This term is a little different from the previous one, but it is also indivisible from central sensitization. Allodynia occurs when the patient abnormally perceives pain in response to a process that does not normally cause it., such as rubbing against a surface or simple palpation of the affected surface.

There are 3 types of allodynia: static mechanics, dynamic and thermal mechanics. The first is defined by the perception of pain with light manual pressure, such as touching the surface of the skin.

On the other hand, dynamic mechanical allodynia is produced by the repeated application of soft stimuli, such as the passage of a cotton ball or a brush. Lastly, thermal allodynia occurs when the patient presents special reluctance to slightly hot or cold weather events.

Both terms are different, but they are housed within the umbrella of central sensitization. The following idea should be clear to you:

Central sensitization: hyperalgesia + allodynia

Causes of central sensitization

The nickname "central" comes from the fact that, indeed, the problem is located in the Central Nervous System (CNS): the brain and spinal cord. As we have said, the neurons in charge of perceiving pain amplify the signal and make it stronger, which is why the patient perceives atypical pain in routine events.

In any case, neurons not only send amplified signals, but also transmit “erroneous” information, producing abnormal responses by the organism to environmental stimuli currents. It must be taken into account that, in order to understand central sensitization, it is necessary to factor in the fact that there are predisposing and precipitating factors.

1. predisposing

Although this series of pathologies are very little known, it is known that there is a certain genetic inheritance for their appearance. core sensitization it usually runs in families and, in addition, it seems that people who have suffered abuse or traumatic events during childhood are more likely to present it.

2. precipitants

In people with a predisposition, there is usually a precipitant or trigger that causes the appearance of central sensitization. Something as simple as a viral infection can cause it, but it usually happens after accidents and serious injuries, both physical and emotional..

As studies indicate, a painful stimulus of great intensity can be the prelude to a series of functional and morphological characteristics in the central nervous system (CNS), which translates into the general picture of central sensitization that we see here. regards

Some examples of central sensitization

So far we have talked about central sensitization as a kind of pathology, but this is not exactly the case. This is a common event in several diseases characterized by chronic pain. We briefly tell you about some of them.

fibromyalgia

Is about a disorder characterized by the presence of widespread musculoskeletal pain, which interferes with the ability to rest, memory and general mood of the patient.

Fibromyalgia usually finds its causes in hereditary factors, infections, and physical and emotional trauma. Something like a car accident or a traumatic situation can lead to the appearance of this chronic pathology, although it may not seem like it. It is estimated that in certain countries the total prevalence is located at 2.4% of the general older population 20 years (generally between 35 and 55 years), being 6 to 8 times more common in women than in men.

Chronic Fatigue Syndrome

Chronic fatigue syndrome is a serious condition that simultaneously affects many systems in the body. This is characterized by severe fatigue that makes it impossible to carry out routine actions, sleep problems, difficulty concentrating, widespread pain and recurring dizziness.

In the United States alone, an estimated 836,000 to 2.5 million people have chronic fatigue syndrome. This occurs mostly in people between the ages of 40 and 60 and, again, it is more common in women than in men.

• You may be interested in: "Chronic Fatigue Syndrome: Symptoms, Causes, and Treatment"

Irritable bowel syndrome (IBS)

Perhaps this pathology sounds more familiar to you, right? Well yes, even if you didn't suspect it beforehand, irritable bowel syndrome and central sensitivity are highly correlated.

In a society increasingly dominated by stress and worry, IBS occurs in up to 20% of the global population, depending on the population focus consulted and the socioeconomic conditions that exist there. Various factors codify its appearance: genetic, health, dietary, cultural and emotional, among others.

The most common symptom of this pathology is chronic abdominal pain, accompanied by colic and swelling. that is usually alleviated totally or partially when it comes to evacuating the intestines (defeating or passing gases). It also causes the appearance of diarrhea or constipation and mucus in the stool, among other things.

Diseases without treatments

Unfortunately, diseases that present with central sensitization are largely unknown and therefore treatments are limited. In most cases, the aim is for the patient to learn to manage their pain and minimize it, but it is never completely eliminated..

For example, drugs such as pain relievers, antidepressants, and anticonvulsants (epilepsy drugs) have shown to be effective for some cases of chronic pain, although it is not an effective treatment in a universal. All this must be accompanied by robust psychological care for the patient, dominated by physiotherapy, occupational therapy and psychological counselling, among other things.

Summary

As you may have seen, central sensitization is a very little known general pathological picture, since the causes are never elucidated in many patients. If anything is known, it is that it manifests itself in the form of hyperalgesia and allodynia and that, furthermore, it is part of a large number of diseases.

Unfortunately, in most cases little remains beyond resistance and resignation in the patients who suffer from it. Sometimes chronic pain cannot be addressed and therefore it is only necessary to live with it and learn to manage it.

Bibliographic references:

• Azkue, J. J., Ortiz, V., Torre, F., & Aguilera, L. (2007). Central Sensitization in the pathophysiology of pain. Bilbao Medical Gazette, 104(4): pp. 136 - 140.
• Fleming, K. C., & Volcheck, M. m. (2015). Central sensitization syndrome and the initial evaluation of a patient with fibromyalgia: a review. Rambam Maimonides medical journal, 6(2).
• M Adams, L., & C Turk, D. (2015). Psychosocial factors and central sensitivity syndromes. Current rheumatology reviews, 11(2): pp. 96 - 108.
• Serrano-Muñoz, D., Gómez-Soriano, J., Ávila-Martín, G., Galán-Arriero, I., Romero-Muñoz, L. M., Taylor, J. S., & Barriga-Martín, A. (2016). Central pain sensitization in people with whiplash syndrome: a review. Latin American Journal of Orthopedic Surgery, 1(3): pp. 102 - 107.
• Solà, J. F. (2018). Central sensitization syndromes: towards the structuring of a multidisciplinary concept. Clinical Medicine, 151(2): pp. 68 - 70.