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Central Sensitization and its Role in Chronic Pain

A Question and Answer with Dr. David Yu, M.D.

By David Yu, MD

Central Sensitization and its Role in Chronic Pain
This article originally appeared in the Fall 2015 issue of Spondylitis Plus, the quarterly news magazine of Spondylitis Association of America. Members receive every copy of Spondylitis Plus in the mail for free.

Pain: We'd do just about anything to be rid of it. It can take over the body, the mind, and seem to develop a life of its own. But are there different kinds of pain? Different mechanisms at work requiring different approaches? We sat down with Dr. Yu to speak about all of this and more.

Does pain serve a purpose?

A major factor in why the human race has survived is because humans can sense pain.

We sense pain quite frequently in everyday life, e.g. when we touch a needle point by accident. The purpose of this type of acute pain appears to be to prompt us to withdraw from harm.

The purpose of chronic pain, in which the duration exceeds several months, is different. Almost always the cause resides inside of us, e.g. a tumor in the liver or inflammation of the spine. As a matter of fact the simplest explanation for the pain of spondyloarthritis is that it is caused by inflammation in the spine and elsewhere. The apparent purpose of chronic pain is to alert the individual to correct the pathology.

How many people have chronic pain in the U.S.?

As many as 19% of adults in the U.S. are experiencing chronic pain, and half of those report that their pain levels are very high. Surprisingly, at least 1% of adults experience significant and wide-spread chronic pain when there is no obvious pathology, a condition called fibromyalgia. It is believed that the pain of fibromyalgia is the archetype of what is known as central pain.

What is central pain?

The sensation of pain is processed by our nervous system. The nervous system consists of three different structures: the brain, the spinal cord, and the peripheral nerves. When my finger is in contact with a sharp needle, the pain signal is first transmitted from my finger to the spinal cord, then upwards to the brain. At least two compartments of my brain process this signal in the context of all my past experience as well as my current psychosocial state. The human brain, being the most highly developed among animals, is capable of modifying our response to the cause of pain, e.g. keep on running in spite of pain in order to finish a marathon. The command from the brain is then transmitted once more via the spinal cord back to the peripheral nerves. Here, in some cases, sustained pain signaling creates alterations in the nervous system, leading to a lowering of the pain threshold and the enhancement of pain intensity, a process nick-named “wind-up” which involves neurotransmitters glutamate and substance P, among others. “Wind-up” in both the spinal cord and the brain are responsible for central pain. It is termed “central” because the brain and the spinal cord together comprise the central nervous system. The human mind is an extremely creative structure; it can generate and moderate belief systems, sadness and happiness, courage and cowardice, spirituality or analyticity, dignity or indifference, completely independent of external events. Not only that, the mind which the brain generates, differs from person to person, varies from hour to hour, with an infinite degree of variety.

With the onset of modern technologies, such as functional MRI, it is now believed that central pain is generated partly by our central nervous system itself, disproportional to outside events both in intensity and in duration. When a patient with arthritis senses disproportionately enhanced pain relative to the extent of arthritis, the process is termed “central sensitization”.

What is the role of central pain in arthritis?

Although the pain of arthritis is initiated by inflammation of the musculoskeletal system, central pain becomes a critical factor when the central nervous system modifies the sensation of pain to become disproportional to the degree of inflammation. I have seen for example patients with severe and active rheumatoid arthritis who feel very little pain. More frequently, I see patients with minor inflammation who are in severe pain. The prevalence of central pain in arthritis is best studied with rheumatoid arthritis - about 25% of patients with rheumatoid arthritis also have features of central pain/fibromyalgia. That number is lower in ankylosing spondylitis, with about 15% of AS patients having central pain/fibromyalgia features.

How important is it to determine if central pain contributes to the suffering of an arthritis patient?

It is critical for a physician to distinguish central pain from pain caused by the arthritis alone. Central pain is not relieved by standard arthritis medications such as acetaminophen, naproxen or even biologics.

How do doctors diagnose central pain?

Extreme central pain as we see in fibromyalgia is easily recognized by several features.
  1. Pain is widespread. Patients usually describe the pain as involving the entire body.
  2. It is associated to varying degrees with feelings of exhaustion, being un-refreshed after waking up from sleep, and lack of clarity in thoughts.
  3. It is often associated with mood changes such as depression and anxiety, and somatic complaints such as headache, diarrhea, and bladder spasm.
Other than the pattern of symptoms, there are no physical signs, laboratory tests, or clinically applicable imaging tools to diagnose fibromyalgia.

Can fibromyalgia be misdiagnosed as spondyloarthritis?

In general, rheumatologists are physicians who are familiar with both fibromyalgia and spondyloarthritis. They diagnose fibromyalgia and spondyloarthritis by the patterns of symptoms, physical signs, laboratory tests and imaging tests. For both spondyloarthritis and fibromyalgia, even negative laboratory tests and imaging tests, as well as negative physical signs, are important. However, there is no infallible diagnostic formula. The ultimate decision depends on the judgment of the physician.

A major challenge is that both fibromyalgia and spondyloarthritis are spectrums of disorders. The patterns of diseases can be florid or subtle. In addition, regardless of having fibromyalgia or not, in any subject, all pain is colored by past experiences, current events, future aspirations, moods of depression or anxiety, and even purposefulness in life. How a physician interprets reports of pain by a particular patient is also colored by the physician’s own experiences and sense of selfness.

Not infrequently, a single visit to a physician is insufficient. Often times the true diagnosis will unfold with time.

Can changes in mood affect the sensation of pain?

There is a great deal of variations among patients. In general, even with patients carrying an irrefutable diagnosis of spondyloarthritis, changes in mood can affect the severity of pain felt regardless of whether or not a spondyloarthritis patient is being inflicted with central pain. As emotion is part of the constitution of a person, a patient should be aware of their mood, and whether changes in mood affect the severity of their pain.

Are there medications for central pain?

Several drugs have been approved by the FDA for the treatment of fibromyalgia. About one in five to one in ten patients might experience a 30% or more improvement in pain with these medications. In treating central pain, it is best to combine medications with non-pharmacological measures.

Which non-pharmacological measures are useful for control of central pain?

Non-pharmacological measures for central pain are useful for all patients with spondyloarthritis pain, regardless of the degree of contribution by central pain mechanisms. I advocate all patients to consider them seriously. An ideal management of central pain is an interdisciplinary form of pain management. The first step is education about spondyloarthritis, which is what the Spondylitis Association of America is providing.

The most effective modality for alleviating central pain is exercise. The exercises should preferably be of an aerobic type, such as fast walking for 20 minutes, three times a week.

Another useful modality is to train patients to recognize how their perception of pain is modulated by their mood, and how the mood leads to changes in behavior. For example, a depressed individual may feel more pain than they normally would, and become more withdrawn in an apparent attempt to avoid pain. This mood-behavior pattern leads to a vicious cycle. The training to break the cycle is termed “cognitive behavior therapy,” and is commonly practiced by psychologists. In a way, support groups are a form of cognitive behavior therapy.

Cognitive behavior therapists also use mind exercises. Examples of this would be relaxation exercises such as meditation, breathing exercises, and imagery. When properly carried out, relaxation exercises lighten the anxiety and depression related with central pain and help break the pain cycle. Training in these relaxation exercises can be expedited by biofeedback.

What is the most important message in this Q & A?

If you are not sure, ask your doctor how much of your pain might be from central sensitization.


David Yu, MD

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