Clinical overlap between fibromyalgia and myalgic encephalomyelitis. A systematic review and meta-analysis.
Ramírez-Morales, Ricardo, Bermúdez-Benítez, Elyzabeth, Martínez-Martínez, Laura-Aline et al. · Autoimmunity reviews · 2022 · DOI
Quick Summary
This study looked at how often fibromyalgia and ME/CFS occur together in the same patients by reviewing 21 published research papers. The researchers found that nearly half of people diagnosed with one condition also had the other condition. This overlap suggests these two illnesses share common features, particularly fatigue, unrefreshing sleep, and brain fog.
Why It Matters
Understanding the overlap between fibromyalgia and ME/CFS is crucial because patients with both conditions may benefit from integrated diagnostic approaches and tailored treatment strategies. This finding validates the lived experience of many patients who struggle with overlapping symptoms and helps guide clinicians in recognizing and diagnosing these interconnected conditions more effectively.
Observed Findings
Nearly half (47.3%) of reported cases showed overlapping diagnoses of fibromyalgia and ME/CFS across the 21 reviewed studies.
The 2016 revised fibromyalgia diagnostic criteria incorporate three ME/CFS-specific features: fatigue, unrefreshed sleep, and dyscognition.
Studies examined were highly heterogeneous (98% heterogeneity index) in design, objectives, sample size, and diagnostic criteria used.
Most analyzed publications used the older 1990 fibromyalgia diagnostic criteria rather than more recent classification systems.
Fibromyalgia and ME/CFS demonstrate prominent clinical overlap, suggesting shared pathophysiological mechanisms or common diagnostic features.
The reported 47.3% overlap likely underestimates true concordance because most studies used older diagnostic criteria that do not fully capture ME/CFS-specific symptoms.
Use of updated 2016 FM criteria (which includes ME/CFS features) would probably yield higher estimates of clinical overlap.
Remaining Questions
Do fibromyalgia and ME/CFS represent distinct diseases with overlapping symptoms, the same underlying condition with different presentations, or a spectrum of related disorders?
What This Study Does Not Prove
This meta-analysis demonstrates correlation and overlap but does not establish whether fibromyalgia and ME/CFS are the same disease, distinct disorders with shared features, or whether one causes the other. The high heterogeneity across studies and reliance on older diagnostic criteria means the true overlap may differ from the reported 47.3% estimate. The study cannot determine causative mechanisms or explain why these conditions co-occur.
What are the biological mechanisms explaining why these conditions co-occur in nearly half of cases?
How would overlap estimates change if all studies used the 2016 fibromyalgia criteria instead of older diagnostic frameworks?
Are there distinct patient subgroups with FM-predominant, ME/CFS-predominant, or truly overlapping phenotypes with different prognoses and treatment responses?