Diagnostic Criteria for Fibromyalgia
The American College of Rheumatology (ACR) 1990 criteria remain the most widely used diagnostic standard, requiring chronic widespread pain for >3 months plus tenderness at ≥11 of 18 specific tender point sites, though the 2010 modified criteria offer a practical alternative that eliminates the need for tender point examination. 1, 2
ACR 1990 Classification Criteria (Traditional Standard)
The 1990 criteria require both of the following 3:
Widespread pain present for ≥3 months, defined as pain in all four body quadrants:
Tenderness at ≥11 of 18 specific tender point sites upon digital palpation with approximately 4 kg/cm² of pressure 4, 3
- The patient must perceive the palpation as painful, not merely tender 4
Important Caveat About Tender Points
The focus on tender points has been increasingly criticized over the past two decades, as this criterion proved problematic in clinical practice and did not adequately capture the full spectrum of fibromyalgia symptoms 4, 5, 6. Many clinicians found the tender point examination unreliable and overly restrictive.
ACR 2010 Diagnostic Criteria (Modern Alternative)
The 2010 criteria shifted away from tender points to a symptom-based approach 4, 5:
Fibromyalgia is diagnosed when:
- Widespread Pain Index (WPI) ≥7 AND Symptom Severity (SS) Scale ≥5 4
Widespread Pain Index (WPI)
- Count the number of painful body regions (0-19 possible sites) 4
Symptom Severity Scale (SS)
- Rate severity (0-3) of: cognitive symptoms, unrefreshed sleep, fatigue 4
- Add count of somatic symptoms 4
- Total SS score ranges 0-12 4
Modified 2010 Criteria
A simplified version removed physician assessment of somatic symptoms and replaced it with self-reported symptom scores, making it easier to use while maintaining sensitivity 5.
Essential Clinical Features Beyond Criteria
Fibromyalgia presents as a central pain processing disorder with characteristic associated symptoms 1, 4:
- Chronic widespread pain with reduced pain threshold, hyperalgesia, and allodynia 1
- Fatigue (prominent and disabling) 1, 4
- Sleep disturbance (unrefreshed sleep) 1, 4
- Cognitive dysfunction (memory problems, "fibro fog") 1, 4
- Depression and anxiety (frequently comorbid) 1
- Additional somatic symptoms: headache, migraine, irritable bowel symptoms, diffuse abdominal pain, urinary frequency 1
Required Laboratory Screening to Exclude Mimics
Basic laboratory tests are mandatory to rule out inflammatory, endocrine, and other organic diseases 2:
- Erythrocyte sedimentation rate (ESR) 2
- C-reactive protein (CRP) 2
- Thyroid function tests 2
- Creatine kinase 2
- Vitamin D levels 2
These tests should be normal in fibromyalgia; abnormalities suggest alternative diagnoses 6.
Critical Differential Diagnoses to Exclude
Before diagnosing fibromyalgia, systematically rule out 6, 7:
- Systemic rheumatic diseases (rheumatoid arthritis, systemic lupus erythematosus, polymyalgia rheumatica)
- Inflammatory myopathies (polymyositis, dermatomyositis)
- Endocrine disorders (hypothyroidism, hyperparathyroidism)
- Neurologic conditions (multiple sclerosis, myasthenia gravis)
- Primary psychiatric disorders (major depression, generalized anxiety disorder) 6
Overlapping Central Sensitivity Syndromes
Fibromyalgia frequently coexists with other central sensitivity syndromes 7:
- Chronic fatigue syndrome/myalgic encephalomyelitis 1, 7
- Irritable bowel syndrome 7
- Migraine 2, 7
- Temporomandibular disorder 7
These conditions share central sensitization as a common pathogenic mechanism 7.
Functional Assessment Tools
Use validated instruments to quantify disease impact 1, 2:
- Fibromyalgia Impact Questionnaire (FIQ) - measures functional impairment and treatment response 1, 2
- Visual Analogue Scale (VAS) - assesses pain intensity 1, 2
Common Diagnostic Pitfalls
- Do not rely solely on tender points - the 1990 criteria's emphasis on tender points is outdated and misses many patients with genuine fibromyalgia 5, 6
- Do not diagnose fibromyalgia without excluding organic disease - laboratory screening is essential 2, 6
- Do not dismiss psychiatric comorbidity - carefully evaluate for primary mood disorders, as these are highly prevalent and require separate treatment 6
- Do not assume fibromyalgia is a diagnosis of exclusion - it has positive diagnostic features (widespread pain, characteristic symptoms, central sensitization) 4, 7
- Recognize that fibromyalgia can coexist with other rheumatic diseases - the presence of rheumatoid arthritis or lupus does not exclude fibromyalgia 3