Fibromyalgia Diagnostic Criteria
Fibromyalgia is diagnosed clinically using the American College of Rheumatology (ACR) criteria, which focus on chronic widespread pain lasting at least 3 months combined with a Widespread Pain Index (WPI) ≥7 and Symptom Severity (SS) scale ≥5, eliminating the outdated requirement for tender point examination. 1, 2
Modern ACR Diagnostic Criteria (2010-Present)
The current diagnostic approach requires:
- Widespread Pain Index (WPI) ≥7 AND Symptom Severity (SS) scale ≥5 as the primary diagnostic threshold 2, 3
- Chronic widespread pain present for at least 3 months in all four body quadrants (left side, right side, above waist, below waist) plus axial skeletal pain 1, 2
- The SS scale incorporates categorical ratings for cognitive symptoms, unrefreshed sleep, fatigue, and number of somatic symptoms 2
The 1990 tender point criteria (requiring 11 of 18 tender points with 4 kg/cm² pressure) are no longer recommended, as the focus on tender points was not justified and has been replaced by the more comprehensive symptom-based approach 2, 4
Core Clinical Features Required
- Pain characteristics: Chronic widespread pain with hyperalgesia and allodynia present in all four body quadrants for minimum 3 months 1
- Fatigue: Disproportionate to activity level 1, 3
- Sleep disturbances: Non-restorative sleep 1, 3
- Cognitive dysfunction: Often described as "fibro fog" 1, 3
Associated Symptoms That Strengthen Diagnosis
- Mood disturbances including anxiety and depression 1
- Stiffness 5
- Multiple somatic symptoms that overlap with other central sensitivity syndromes 6, 5
Screening Tools
- Fibromyalgia Rapid Screening Tool is recommended for initial screening in patients presenting with diffuse chronic pain 3
- The Fibromyalgia Impact Questionnaire (FIQ) measures functional impairment and impact on daily activities, though it is used for assessment rather than diagnosis 1
Essential Laboratory Exclusion Testing
Basic laboratory screening is required to exclude mimicking conditions, not to diagnose fibromyalgia:
- Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) to exclude inflammatory diseases 1
- Thyroid function tests to exclude endocrine disorders 1
- Creatine kinase to rule out myopathies 1
- Vitamin D levels 1
There are no laboratory abnormalities that confirm fibromyalgia—it remains a clinical diagnosis 4
Critical Diagnostic Pitfalls to Avoid
- Do not treat fibromyalgia as a diagnosis of exclusion—it is a positive clinical diagnosis based on specific criteria 4
- Do not perform tender point examination as the primary diagnostic method, as this outdated approach has been replaced by the WPI and SS scale 2
- Do not order excessive testing—establishing the diagnosis early can reassure patients and decrease unnecessary healthcare utilization, which averages 3.7 consultations with different physicians over 2+ years when diagnosis is delayed 1, 3
- Do not assume unilateral or focal symptoms rule out fibromyalgia, but investigate these thoroughly as they may represent comorbid conditions requiring separate treatment 7
Differential Diagnoses to Consider
- Chronic fatigue syndrome may coexist or present similarly 1, 6
- Post-Lyme disease syndrome can fulfill fibromyalgia criteria with multiple tender points and widespread pain 1
- Other central sensitivity syndromes including irritable bowel syndrome, temporomandibular disorder, and interstitial cystitis frequently overlap 6, 5
- Rheumatologic conditions may coexist with fibromyalgia and require separate evaluation 6