What is the diagnostic workup for a patient with suspected fibromyalgia?

Diagnostic Workup for Fibromyalgia

The diagnostic workup for fibromyalgia is primarily clinical, requiring documentation of chronic widespread pain for at least 3 months plus comprehensive assessment of associated symptoms, followed by targeted laboratory testing to exclude mimicking conditions—not to confirm fibromyalgia itself. 1

Clinical Assessment

History Taking

Document the following specific features:

• Pain characteristics: Chronic pain present in all four body quadrants for minimum 3 months, with hyperalgesia (increased pain response) and allodynia (pain from normally non-painful stimuli) 2
• Associated symptoms: Fatigue disproportionate to activity level, non-restorative sleep, cognitive dysfunction ("fibro fog"), and mood disturbances including anxiety and depression 2, 3
• Functional impact: Use the Fibromyalgia Impact Questionnaire (FIQ) to quantify impairment in daily activities, pain intensity, fatigue, sleep quality, and overall functioning 2
• Demographic context: Note that fibromyalgia affects approximately 2% of the population, predominantly women aged 30-60 years 2, 3
• Environmental triggers: Specifically inquire about alcohol, sleep deprivation, emotional stress, large meals, caffeine, and exercise as potential precipitants 1

Physical Examination

The tender point examination remains clinically useful despite newer criteria:

• Apply approximately 4 kg of pressure (sufficient to blanch your fingernail bed) to 18 specific bilateral anatomical sites: occiput, lower cervical spine, trapezius, supraspinatus, second rib, lateral epicondyle, gluteus, greater trochanter, and knee 2
• A positive tender point requires the patient to report pain (not just tenderness) upon digital palpation 2
• The 1990 ACR criteria require pain in at least 11 of 18 tender points, though the 2010 criteria moved away from this requirement 2, 4

Laboratory Workup

Order the following tests to exclude mimicking conditions, not to diagnose fibromyalgia:

• Basic inflammatory markers: Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) to exclude inflammatory arthropathies 2
• Thyroid function tests: TSH and free T4 to exclude hypothyroidism 2, 5
• Creatine kinase: To exclude inflammatory myopathies 2
• Vitamin D level: To exclude vitamin D deficiency causing musculoskeletal pain 2
• Complete blood count: To exclude anemia contributing to fatigue 5

Critical caveat: There are no laboratory abnormalities that confirm fibromyalgia—all tests should be normal. If abnormalities are found, pursue alternative diagnoses. 6, 5

Differential Diagnosis Considerations

Actively exclude these conditions that can mimic fibromyalgia:

• Endocrine disorders: Hypothyroidism, hyperparathyroidism, Cushing's syndrome 5
• Rheumatologic diseases: Polymyalgia rheumatica, rheumatoid arthritis, systemic lupus erythematosus 5, 4
• Neurologic disorders: Multiple sclerosis, myasthenia gravis, peripheral neuropathy 5
• Medication-related causes: Statin-induced myopathy, corticosteroid withdrawal 5
• Overlapping syndromes: Chronic fatigue syndrome, irritable bowel syndrome, post-Lyme disease syndrome 2

Diagnostic Criteria Application

Use the American College of Rheumatology criteria for diagnosis:

The 1990 ACR criteria require both: (1) widespread pain for at least 3 months, and (2) pain in at least 11 of 18 tender points on digital palpation. 2, 4

The 2010 ACR criteria (and subsequent modifications) use a symptom-based approach without tender point examination, incorporating the Widespread Pain Index and Symptom Severity Scale. 3

The Fibromyalgia Rapid Screening Tool can be used for initial screening in patients with diffuse chronic pain. 3

Psychosocial Assessment

Screen for psychiatric comorbidities that commonly coexist:

• Depression and anxiety disorders (present in majority of patients) 2, 3
• History of physical or emotional trauma 4
• Sleep disorders beyond fibromyalgia-related sleep disturbance 5
• Active suicidal ideation (requires immediate psychiatric referral) 7

Common Pitfalls to Avoid

Do not treat fibromyalgia as a diagnosis of exclusion—it is a positive clinical diagnosis based on characteristic features. 6

Do not order extensive imaging or specialized testing unless specific findings on history or physical examination suggest alternative diagnoses. Routine chest radiography and echocardiography are not indicated. 5

Do not delay diagnosis while pursuing unnecessary testing—the average patient sees 3.7 different physicians over more than 2 years before diagnosis, leading to excessive healthcare utilization. 2

Establish the diagnosis promptly and provide patient education, as this alone can significantly reduce healthcare costs and improve patient reassurance. 2, 3