Is fibromyalgia similar to ME/CFS?


  • There is considerable debate about whether fibromyalgia and ME/CFS are similar or different illnesses
  • This systematic review of 21 studies found a clinical overlap with ME/CFS in about half of fibromyalgia patients
  • The findings suggest the illnesses share some disease-causing mechanisms such as infection or genetic factors


For many years, researchers have tried to distinguish between ME/CFS and fibromyalgia (FM). While both illnesses share some common symptoms such as pain and fatigue, there are marked differences in their apparent causes and presentation.

These differences have led to uncertainty about whether ME/CFS and fibromyalgia are similar or different illnesses, or even whether they are different presentations on a spectrum that includes both diseases.

Researchers in Mexico recently published the results of a systematic review and meta-analysis of the available research (comprising 21 studies) addressing this question of whether there is a clinical overlap.

A meta-analysis is way of pooling the results of several studies to look at overall trends in a larger number of patients than will have been investigated in any individual study.

What did they find?

The authors found that most of the 21 studies differed in their design, objectives, sample size, diagnostic criteria and/or outcomes, resulting in what is known as a high degree of heterogeneity, which makes comparisons between them difficult.

Nevertheless, the authors report that there is a well-defined clinical overlap between ME/CFS and FM. Almost half of FM patients met diagnostic criteria for ME/CFS.

Most of the 21 studies used the 1990 Wolfe diagnostic criteria for FM. It is possible that the overlap between conditions would have been higher if the studies had used the more recent 2016 diagnostic guidelines, which incorporate three key ME/CFS features: fatigue, waking unrefreshed and cognitive symptoms.

What does this mean?

The authors speculate that the overlap between ME/CFS and FM might reflect a similar underlying cause, such as a history of viral infection resulting in dysfunction of the autonomic nervous system and chronic inflammation. However, FM patients report higher rates of previous physical injury or psychological stress than do people with ME/CFS.

Inflammation of the dorsal root ganglia (an area of the spinal cord that detects things like pain and temperature) is believed to play a role in both conditions, possibly resulting in the activation of chronic pain, although this is a complex area.

It is possible that inflammation of the central nervous system is as important in FM as it is in ME/CFS. However, FM is often characterised by points of tenderness on the body, joints and muscles, while non-specific, generalised pain (in response to physical activity) is more common in ME/CFS.

Overall, this study reported that almost half of patients who meet criteria for FM could also meet criteria for ME/CFS, while another study suggests that around a third of all patients attending pain clinics could receive an ME/CFS diagnosis.

Some caution needs to be applied here. Overlapping symptoms do not mean that FM and ME/CFS can be considered the same condition or a spectrum of the same condition – there are important similarities between them, but some important differences also.

Newer criteria for diagnosing FM appear more aligned with ME/CFS criteria, but more research is needed to draw more definitive conclusions.

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