There’s substantial research suggesting that it might be – and substantial research suggesting it isn’t.
Approximately 95% of those with chronic fatigue syndrome have diffuse pain in addition to chronic fatigue.
Over 75% of those with fibromyalgia report extreme, often debilitating fatigue.
Approximately half of those with either diagnosis meet the formal diagnostic criteria for the other.
Both conditions have been associated with excess activation of NF-kB, pro-inflammatory cytokine elevation and certain other dysfunctions in the inflammatory response system.
All of the above suggests that we may be dealing with two variations of a single underlying problem.
One notable difference between the two is that a far higher percentage of men comprise those with chronic fatigue syndrome vs. the percentage of men found among those with fibromyalgia. However, it’s interesting to consider this difference in light of the fact that in nearly any condition associated with pain, women report experiencing more pain, more often, in more locations.
The formal diagnostic criteria for fibromyalgia requires pain in response to pressure on at least 11 of 18 identified locations. That criteria is of course rather arbitrary. If someone has pain at only 10 such locations do they not have fibromyalgia? According to the formal criteria they would not.
It’s important to keep in mind the reason a formal diagnostic criteria for fibromyalgia was initially established. The primary motivation for establishing a very specific definition of fibromyalgia was to allow clinicians, and especially researchers, to know they were all discussing (or studying) the same thing when they compared patients or the results from clinical trials. The number of tender points might just as well have been set at 14 or at 6.
Raising or lowering the bar would result in fewer, or more, people meeting the formal diagnostic criteria. Would that mean more or fewer people having fibromyalgia? Technically, yes. But in reality, the same process is most likely at work in those with 10 tender points (or 8, or 5) as in those with 11 or more.If so, then the same disease process is most likely at work in more than the 50% of chronic fatigue patients who satisfy the formal diagnostic criteria.
Because men experience less pain than women, regardless of the disease, fewer men than women are likely to satisfy any specific criteria for fibromyalgia. Therefore it might make sense to adopt a separate standard diagnostic criteria for men. If we were to do so, I suspect that a much larger percentage of men with chronic fatigue syndrome would then be found to have fibromyalgia as well.
In sum, sharing the formal diagnostic criteria for a syndrome is not the same as sharing the same underlying disease process. It’s likely that a far higher percentage share the underlying process than share the formal diagnosis. So while chronic fatigue syndrome and fibromyalgia initially appear similar, the true similarity may be even greater.
Of course none of this proves that the two conditions are variations on a single entity, let alone that they are ‘the same’. Still, the odds at this point seem to favor a single underlying condition, suggesting there might be a single effective treatment for both.