A four-year follow-up study in fibromyalgia. Relationship to chronic fatigue syndrome.
Nørregaard, J, Bülow, P M, Prescott, E et al. · Scandinavian journal of rheumatology · 1993 · DOI
Quick Summary
This study followed 91 fibromyalgia patients for about 4 years to see if their muscle pain was caused by other medical conditions and how their symptoms changed over time. Most patients reported their pain got worse, and while many experienced severe fatigue, very few actually met the diagnostic criteria for chronic fatigue syndrome. The good news was that muscle strength remained stable and most cases of fibromyalgia were not caused by an underlying disease.
Why It Matters
This study is important because it clarifies the relationship between fibromyalgia and ME/CFS, showing they are distinct conditions despite symptom overlap—particularly fatigue. Understanding that most fibromyalgia cases are not secondary to other diseases helps researchers and clinicians focus on primary pathophysiological mechanisms. For ME/CFS patients, this work highlights the need for condition-specific diagnostic criteria and recognition that fatigue-dominant presentations may represent different disease entities.
Observed Findings
Only 2 of 91 fibromyalgia patients developed an underlying somatic disease causing their muscle pain during 4-year follow-up
Muscle strength remained stable with no significant decline over the follow-up period
Approximately 80% of fibromyalgia patients reported severe fatigue, but only ~20% met proposed chronic fatigue syndrome diagnostic criteria
Inferred Conclusions
Fibromyalgia is primarily a primary disorder rather than secondary to other somatic diseases in most cases
Fibromyalgia and chronic fatigue syndrome overlap in symptomatology but represent distinct clinical entities with different prevalence rates
Fatigue is common in fibromyalgia but does not automatically indicate concurrent CFS diagnosis
Remaining Questions
What are the pathophysiological mechanisms that cause fatigue in fibromyalgia patients who do not meet CFS criteria?
Why do some fibromyalgia patients show pain progression while others improve, and can we identify predictive biomarkers?
How would fibromyalgia-CFS overlap rates change using current diagnostic criteria (e.g., ICC 2011 ME/CFS criteria)?
What This Study Does Not Prove
This study does not establish that ME/CFS and fibromyalgia never co-occur or are mutually exclusive; it only shows most fibromyalgia patients do not meet CFS criteria. The study does not identify the underlying causes of fibromyalgia or explain the mechanisms linking the two conditions. Additionally, 1993 diagnostic criteria for CFS differ from current definitions, so the actual overlap rate may differ with modern case definitions.
Tags
Symptom:PainFatigue
Method Flag:PEM Not DefinedWeak Case DefinitionNo Controls