What are the diagnostic criteria for fibromyalgia?

Diagnosing Fibromyalgia

According to the American College of Rheumatology (ACR) criteria, fibromyalgia is diagnosed based on the widespread pain index (WPI), symptom severity scale (SS), and a history of generalized pain present for at least 3 months. 1

Current Diagnostic Criteria

The diagnostic approach has evolved over time from the 1990 ACR criteria to the 2010 preliminary diagnostic criteria:

2010 ACR Preliminary Diagnostic Criteria (Current Standard)

• Diagnosis is made when either of these conditions are met:

  • WPI ≥7 AND SS ≥5, OR
  • WPI 3-6 AND SS ≥9 2

• Widespread Pain Index (WPI): Measures the number of painful body regions (score range: 0-19)

• Symptom Severity Scale (SS): Assesses:

  • Cognitive symptoms
  • Unrefreshing sleep
  • Fatigue
  • Number of somatic symptoms 1, 2

• Additional requirement: Symptoms have been present at a similar level for at least 3 months

Historical 1990 ACR Classification Criteria

• History of widespread pain for at least 3 months
• Pain upon digital pressure (approximately 4 kg) in at least 11 of 18 tender points 1

Key Diagnostic Elements

1. Chronic widespread musculoskeletal pain

   • Present for at least 3 months
   • Affecting multiple body regions

2. Associated symptoms to evaluate:

   • Fatigue
   • Unrefreshing sleep
   • Cognitive difficulties ("fibro fog")
   • Physical exhaustion
   • Stiffness 3, 4

3. No laboratory abnormalities

   • Diagnosis is clinical
   • Laboratory tests are used to exclude other conditions 5

Diagnostic Process

1. Comprehensive symptom assessment:

   • Document pain distribution using WPI
   • Assess symptom severity using SS scale
   • Evaluate duration of symptoms

2. Exclusion of other conditions:

   • Fibromyalgia is not a diagnosis of exclusion, but other conditions must be ruled out
   • Systemic and rheumatic diseases should be excluded through:
     • Patient history
     • Physical examination
     • Targeted laboratory investigations 4

Common Diagnostic Pitfalls

1. Overreliance on tender points:

   • The 2010 criteria eliminated the need for tender point examination
   • Many clinicians still incorrectly rely exclusively on tender points 4, 2

2. Failure to recognize overlapping conditions:

   • Fibromyalgia often coexists with other central pain disorders:
     • Irritable bowel syndrome
     • Chronic fatigue syndrome
     • Migraine 4

3. Missing psychiatric comorbidities:

   • Higher prevalence of psychiatric disorders in fibromyalgia patients
   • Careful evaluation for mood disorders is essential 4

4. Incomplete symptom assessment:

   • Focus only on pain without evaluating other key symptoms
   • Failure to assess symptom duration and severity

5. Lack of standardized approach:

   • No universally accepted "gold standard" for diagnosis
   • All diagnostic criteria should be interpreted with caution 4

By following these diagnostic criteria and avoiding common pitfalls, clinicians can accurately diagnose fibromyalgia and develop appropriate treatment plans for patients suffering from this challenging condition.