CFS and Fibromyalgia
Caused by the same disease?
©1996 David A. Nye MD. CFS Connection: The Helping Hand.
Syndromes are defined constellations of symptoms and signs or lab findings. They are different from diseases which are defined by their causes. Anyone who has the symptoms and exam findings that define a syndrome has that syndrome by definition, whatever the underlying disease mechanism. Two different diseases may cause the same syndrome. Two different syndromes may be caused by the same disease.
A diagnosis of fibromyalgia syndrome (FM, or FMS) requires a complaint of aching all over that the finding of at least 11 out of 18 tender points on examination. A diagnosis of chronic fatigue syndrome (CFS, or CFIDS; also called myalgic encephalomyelitis, or ME, in the UK and Canada) requires that other criteria be met, including disabling fatigue and the presence of a certain number of other signs and symptoms, several of which are also common to FMS.
Although CFS and FMS are differently defined syndromes, it is likely that patients with fibromyalgia and chronic fatigue syndrome have the same underlying disease for a number of reasons. Three quarters of patients who meet the criteria for each do so for the other. It seems unlikely that these patients have two separate diseases. Symptoms are similar in the two disorders. Effective treatments for one often turn out to be effective for the other. Most CFS experts now acknowledge the value of gentle aerobic exercise in treating CFS. In FMS as in CFS, too much or too vigorous exercise is harmful. Similar laboratory abnormalities are now being uncovered in both.
This has lead to the suggestion that the distinction between the two is artificial and exists largely for historical reasons. Perhaps dividing the two disorders on the basis of degree of fatigue relative to pain is no less arbitrary than doing so on the basis on the degree of dizziness, tingling, pelvic pain, or any of the other dozen or more symptoms associated with these disorders.
This is not just a semantic "lumper vs splitter" debate. If FMS and CFS are produced by the same underlying disease process we may be wasting research money and effort and slowing down progress toward discovering their common pathophysiology, not to mention confusing patients and the public, by not combining FMS and CFS research efforts.
The prevalence of FMS is 2-4%, well above the estimated prevalence for CFS. If the two conditions are indeed caused by the same disease, that means that FMS is a more sensitive index for it. It has been estimated that at least 75% of FMS patients become at least 75% better with treatment. In my experience this is somewhat low given recent advances in treatment. The higher reported success of FMS than CFS suggests it might also be more specific, or at least does not achieve its sensitivity at the expense of reduced specificity.
A diagnosis of FMS does not require the extensive and expensive medical workup that CFS does, which requires that other causes of fatigue be excluded. In fact, there is no recommended routine minimum diagnostic evaluation for FMS. Whether this is because the presence of tender points is highly specific for this disease or because the recommended workup is not really necessary merits further study. I have had no FMS patients who turned out later to have a different problem masquerading as FMS and one doesn't read about this problem in the literature.
These considerations suggest that we should use the diagnosis of CFS only in patients why fail to meet diagnostic criteria for FMS, or better yet, allow the diagnosis of a new combined syndrome in some patients who fail the tender point criteria if they meet other symptomatic criteria currently associated with CFS.
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