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Fibromyalgia (FM) and Chronic Fatigue Syndrome (ME/CFS) Similar But Different?

question mark2How similar are chronic fatigue syndrome and fibromyalgia? Are they ‘sister diseases’ – two different types of the same disorder? Or are they totally different diseases that just happen to share many symptoms? One researcher has proposed that both diseases belong to a set of disorders called Central Sensitization Syndromes (CSS’s) that are characterized by increased ‘sensitization’ in different parts of the brain. He believes these two disorders share a problem that is similar in type but different in location. Others think differently

Let’s take a look some similarities and differences….


Perhaps the most striking similarity between the two diseases lies in their symptoms. Both diseases are characterized by pain, fatigue, poor sleep, cognitive problems, increased sensitivities to odors and chemicals, headaches, irritable bowel, orthostatic intolerance (problems standing), poor coordination and more. Mood disorders are common in both diseases but in neither disease are they believed to be a contributing factor. Attempts to separate the two diseases from each other using statistical analyses of their symptoms have largely failed.

Yet they do differ. While both are characterized by both pain and fatigue pain is the dominant symptom in FM and a crushing fatigue is the most dominant symptom in ME/CFS. The pain in FM reaches a kind of intensity not found in CFS while the degree of post-exertional fatigue is much higher in CFS. Unlike FM patients some ME/CFS patients are unable to tolerate more than the smallest amount of activity


Both diseases are reported to be triggered by many of the same events including trauma, physical and/or psychological stress, infection and toxins.

The Type of People Effected

In both diseases middle-aged women of all socioeconomic classes are most commonly affected. According to some reports approximately 70% of CFS patients have FM and vice versa.


Both diseases are defined using symptoms not laboratory measures and controversies rage in both diseases about how to properly define them[/p]


  • Brain and Nervous System These disorders share many central nervous system abnormalities such as reduced blood flows to the thalamus and abnormal activation of the anterior cingulate, reduced gray matter volume, abnormal nervous system activity involving serotonin, increased sympathetic nervous system activity and decreased parasympathetic nervous system activation during sleep and low heart rate variability. Levels of the pro-pain factor substance P, however, are increased in FM but not in CFS. The antiviral enzyme RNase L is fragmented in CFS but not FM. Different sets of gene mutations are associated with each disease.
  • Endocrine Reduced functioning of the stress response in the HPA axis, low cortisol levels are found in both.
  • Others Both ME/CFS and FM patients also display reduced blood flows to the brain and muscles, evidence suggesting mitochondrial abnormalities are present and increased levels of oxidative stress. An unusual activation of the pain response during exercise is also present in both disorders

Societal Acceptance

Perhaps the most important similarity for the CFS/FM patient concerns how well informed the medical profession is of their diseases; both diseases have a high misdiagnosis rate and suffer from poor acceptance by the medical profession.

Different Research Approaches

Some of our confusion about how similar CFS and FM are results from the different approaches researchers have taken towards the two diseases. We know a lot about the immune system in CFS but very little about it in FM. Similarly we know a lot about the functioning of pain pathways in FM but very little about pain production in CFS. As these two diseases get more research we should know more.

The Future

With increased research funding over the past five years and more attention being given to the FM by the pharmaceutical companies the future for the FM patient is looking better. Despite great strides in increasing its legitimacy recently research funding for CFS has remained flat or even declined recently and the outlook there is much poorer.  The creation of an interagency NIH group focusing on fibromyalgia, ME/CFS, irritable bowel syndrome, interstitial cystitis and similar disorders suggests interest is increasing in the ties that may bind these disorders together. Whether that will result in coordinated studies and more funding, however, is unclear.



Latent class analysis of symptoms associated with chronic fatigue syndrome and fibromyalgia.
Sullivan PF, Smith W, Buchwald D., Psychol Med. 2002 Jul;32(5):881-8.

Pain complaints in patients with fibromyalgia versus chronic fatigue syndrome. Bradley LA, McKendree-Smith NL, Alarcon GS. 1: Curr Rev Pain. 2000;4(2):148-57.

Fibromyalgia and overlapping disorders: the unifying concept of Central Sensitivity Syndromes. M. Yunus. 2007. Semin Arthritis Rheum, In press.

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