Fibromyalgia or Chronic Fatigue Syndrome?

By Karen Lee Richards, ChronicPainConnection Lead Expert

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How do you tell whether you have fibromyalgia, chronic fatigue syndrome (also known as “Myalgic Encephalopathy” or “ME”) or both? Are they completely unrelated disorders, sister illnesses that share similar symptoms, or one disease with two different names?

Although there is still some disagreement among experts, most believe they are two distinct disorders that have a number of symptoms in common. However, distinguishing one from the other can be difficult. Further complicating the situation is the fact that approximately 70 percent of people who have one also have the other.


Some of the most common symptoms that may be found in both FM and ME/CFS are debilitating fatigue, muscle and/or joint pain, difficulty with memory, concentration and cognitive functioning, depression, headaches, sleep disturbances, dry eyes and mouth, morning stiffness, and numbness or tingling. 

There are also clinical similarities:

  • Reduced blood flow in the cerebral cortex and midbrain
  • Hypothalamic pituitary axis (HPA) suppression
  • Disturbed Stage 4 sleep
  • Lower than normal serotonin levels
  • Reduced levels of growth hormone
  • Evidence of a genetic component


A simplified explanation of the difference between fibromyalgia and chronic fatigue syndrome is that pain is the most predominant symptom of fibromyalgia, but fatigue is the most predominant symptom of ME/CFS. More specifically, fibromyalgia is identified by 18 distinct tender points (designated points on the body that are painful when four kilograms of pressure are applied), while chronic fatigue syndrome / ME is distinguished by a post-exertional malaise (deep fatigue and exhaustion following physical exertion, which lasts more than 24 hours).

Additional differences include:

  • Substance P (a neurotransmitter that sends pain signals) is elevated in FM but not in ME/CFS.
  • RNaseL (a cellular antiviral enzyme) is frequently elevated in chronic fatigue syndrome but not in fibromyalgia.
  • ME/CFS is often triggered by an infectious or flu-like illness, while FM is usually triggered by a severe physical or emotional trauma (for example, injury, illness, surgery, prolonged stress).
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