Fibromyalgia and Central Sensitivity

This is a review of a 2015 paper by Dr. Muhammad Yunus who was a key Fibromyalgia researcher since 1983 (the start of the modern era of FM). He is now retired. Throughout this time, he has published several important papers, always respectful of patient’s experiences and focused on what the research tells us.

What is Central Sensitization (CS)?

If you have read about Fibromyalgia in the past decade you will have encountered the term “Central Sensitization”. Central Sensitization (CS) refers to the spinal cord and brain becoming hypersensitive to stimuli. In Session #7 of my manual, I explain many of the concepts connected with Central Sensitization such as allodynia and hyperalgesia. And I describe some of the research studies which prove that the central nervous systems of people with Fibromyalgia (now considered the poster child for Central Sensitivity Syndromes) are hypersensitive to painful stimuli. Conditions that are thought to be caused and perpetuated by Central Sensitization (the brain becoming sensitive to stimuli) are called Central Sensitivity Syndromes.

In this paper, Yunus explains that Fibromyalgia is caused and perpetuated by Central Sensitization as are so many other conditions which are notoriously hard to treat including Irritable Bowel Syndrome, Temporo-Mandibular Disorder, Chronic Headache, chronic pain of many types including pain due to Osteoarthritis, Rheumatoid Arthritis and Small Fibre Neuropathy. Yunus includes Multiple Chemical Sensitivity, Primary Tinnitus (ringing in the ears) and Restless Legs Syndrome in the list of conditions likely caused by Central Sensitization. He does not include ME/CFS saying that there is not (yet) enough evidence that fatigue is caused by Central Sensitization.

Central Sensitization is Measurable and Real

Some of you may be wondering whether Central Sensitization is a merely new term for an old, objectionable concept – psychosomatic illness or somatization. The answer is NO. Central Sensitization exists. There are thousands of studies demonstrating this in animals and humans. It is a measurable, biological reality. In certain circumstances, the brain changes and becomes overly sensitive to stimuli. It is very important to know that sensitization occurs outside of conscious awareness. It is not our fault. Some people are more susceptible due to genetics or earlier injuries or exposures, also not our fault. The brain's ability to change (neuroplasticity) causes these Central Sensitivity Syndromes and because the brain continues to be plastic or changeable, conditions caused by Central Sensitization are reversible no matter how long they have existed.

A quick refresher on the difference between acute and chronic pain. Acute pain is a healthy, protective reaction to tissue damage, inflammation or infection. Signals are sent from the area of injury to the brain and the brain assesses and acts on the danger. The brain sends signals to the muscles, immune, endocrine and other systems of the body to do things to protect itself. Chronic pain is caused by the brain’s adaptation to this initial trigger. Chronic pain continues long after the original tissue damage has healed. Chronic pain is caused and perpetuated by the brain, not the body.

Central Sensitization is the balance between signals going from the body to the brain (usually signalling something is wrong) and signals going from the brain to the body (usually inhibiting pain). These signals and the neurotransmitters which cause them can be measured in research settings. Studies repeatedly show that something is amiss in the brains of people with fibromyalgia and other chronic pain disorders. Interestingly, one of these tests called Conditioned Pain Modulation is consistently abnormal in chronic pain disorders but is normal in people with depression. This suggests that even though Depression is more common in people with chronic pain, Depression and chronic pain are different conditions.

Patients with disorders caused by Central Sensitization are generally hypersensitive not only to pain but also to sound, chemicals and light. The whole central nervous system is ramped up and over-reactive.

Treatment of Central Sensitization

Since Central Sensitization plays such a dominant role in Fibromyalgia and other Central Sensitivity Syndromes, interventions that decrease Central Sensitization are helpful. As mentioned in Session #7 of the manual, the drugs that are most helpful for FM pain include pregabalin which decreases Central Sensitization and duloxetine which increases the inhibitory signals flowing from the brain to the body. New approaches being tested include NMDA receptor blockers (like ketamine and memantine) and others.

Drugs, although sometimes helpful often cause side effects. Non-drug approaches include mindfulness meditation, neuroscience education (Explain Pain for example) and cognitive behavior therapy. A new approach I am experimenting with within my practice is changing the brain by using the healing potential of neuroplasticity. I run two groups teaching these skills: the Transforming Pain group using the work of Dr. Michael Moskowitz and the Neuroplasticity in Action group in which we study and practice several different approaches to rewiring the brain.

Triggers of Central Sensitization in vulnerable individuals include:

• physical trauma
• nerve injury
• diseases like arthritis, MS and lupus
• infection
• drugs – morphine can cause chronic pain
• emotional stress
• neuropathy
• poor sleep

You can see that this list includes many conditions with measurable physical findings. Central Sensitization can occur whether or not there is an underlying condition causing the pain. In the January 2015 newsletter (free on my website) I discuss the evidence for small fibre neuropathy (fewer and abnormal nerve endings in the skin) in FM. So even though FM is considered a Central Sensitivity Syndrome, there are physical findings in many cases. There is evidence of physical abnormalities in several other Central Sensitivity Syndromes including Irritable Bowel Syndrome, Interstitial Cystitis and Vulvodynia. Many Central Sensitivity Syndromes have a combination of observable physical pathology and a hypersensitive central nervous system. It’s not either or, it’s both.

Which conditions have central sensitization as a feature?

A suggested classification requires a Central Sensitivity Syndrome to co-exist with others known to be caused by Central Sensitization. For example, Fibromyalgia and Irritable Bowel Syndrome both exhibit brain hypersensitivity. Disorders such as ES which often co-exist with FM and IBS are therefore likely also Central Sensitivity Syndromes. This is a diagnosis by association.

The second suggestion is to include all conditions which exhibit Central Sensitization in research studies. Yunus reviews the evidence for the inclusion of disorders not previously considered due to Central Sensitization. These include chronic cough, Vulvodynia (chronic vulvar/vaginal pain), Burning Mouth Syndrome and Chronic Tinnitus (ringing in the ears). All of these conditions are resistant to treatment with usual methods. He predicts that the number of included conditions will increase as more research is done.

Brain Imaging

Yunus concludes his paper by explaining that with new imaging technology, we can now measure brain changes in Central Sensitivity Syndromes such as FM. As a result, the distinction between “functional” (psychosomatic) and “organic” (real, medical) conditions is erroneous. Changes in brain connectivity, activity and neurotransmitter activity can be demonstrated using functional MRI and PET scanning. Several of the best-studied Central Sensitivity Syndromes show similar brain findings. This suggests that common mechanisms of brain sensitization are shared by many Central Sensitivity Syndromes.

Yunus says that it is no longer accurate to describe Fibromyalgia as “poorly understood” or “mysterious” because there are too many measurable findings.

At the moment it is still very hard to diagnose FM and other Central Sensitivity Syndromes in the doctor’s office. Hopefully, some of the tests that are used in research will become available to validate a patient's experience and lead to evidence-based treatment.

Author: Eleanor (Ellie) Stein MD FRCP(C)

I am a psychiatrist with a small private practice in Calgary and am an assistant clinical professor in the faculty of medicine at the University of Calgary. Since 2000, I have worked with over 1000 patients, all with ME/CFS, FM and ES. My passion for this field comes from my own struggle with these diseases, my desire to improve my health and then pass on what I learn. My goal is for every patient in Canada to have access to respectful, effective health care within the publicly funded system.  

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