How is fibromyalgia determined in a patient?

Determining Fibromyalgia: Diagnostic Approach

Fibromyalgia is diagnosed using the 1990 American College of Rheumatology (ACR) criteria, which require widespread pain in all four body quadrants for at least 3 months plus pain on palpation in at least 11 of 18 specific tender points. 1

Clinical Diagnostic Criteria

ACR 1990 Classification Criteria (Gold Standard)

• Widespread pain must be present for at least 3 months, defined as pain in the left and right sides of the body, above and below the waist, plus axial skeletal pain (cervical spine, anterior chest, thoracic spine, or low back). 1, 2

• Tender point examination requires pain in at least 11 of 18 specific bilateral anatomical sites when approximately 4 kg of pressure is applied (roughly the amount of pressure needed to blanch the examiner's thumbnail). 1, 2

• The 18 tender points are located at: occiput (bilateral), low cervical (C5-C7), trapezius, supraspinatus, second rib, lateral epicondyle, gluteal, greater trochanter, and knee (bilateral). 2

ACR 2010/2016 Criteria (Clinical Practice Alternative)

• These newer criteria eliminate the tender point examination and are more practical for routine clinical diagnosis, though the 1990 criteria remain the research standard. 2

• The 2010/2016 criteria incorporate assessment of widespread pain index and symptom severity scores, including fatigue, cognitive dysfunction, and sleep disturbances. 3

Essential Clinical Assessment

History and Physical Examination

• Document the distribution and duration of pain, specifically confirming pain in all four body quadrants and axial skeleton for at least 3 months. 1

• Assess associated symptoms including fatigue, nonrestorative sleep, cognitive dysfunction (often described as "fibro fog"), mood disorders, and stiffness. 3, 4

• Screen for overlapping conditions such as irritable bowel syndrome, Raynaud's phenomenon, migraine, heat/cold intolerance, and anxiety/depression, which commonly coexist with fibromyalgia. 5, 6

Laboratory and Imaging Evaluation

• Normal laboratory results support rather than exclude the diagnosis of fibromyalgia, as this is a clinical diagnosis without specific biomarkers. 1

• Obtain basic laboratory tests to exclude organic diseases: complete blood count, erythrocyte sedimentation rate, C-reactive protein, thyroid function tests, creatine kinase, and rheumatoid factor/antinuclear antibodies. 6

• Extensive imaging is not required unless the history or physical examination suggests alternative diagnoses. 3

Critical Diagnostic Considerations

Fibromyalgia is NOT a Diagnosis of Exclusion

• A careful differential diagnosis is mandatory, but fibromyalgia can be diagnosed positively when criteria are met, even in the presence of other conditions. 5

• Rule out systemic rheumatic diseases (rheumatoid arthritis, systemic lupus erythematosus, polymyalgia rheumatica), inflammatory myopathies, hypothyroidism, and vitamin D deficiency through history, examination, and targeted laboratory testing. 6

Understanding the Pathophysiology

• Fibromyalgia is characterized by central sensitization and abnormal pain processing, not peripheral tissue damage or inflammation, which distinguishes it from inflammatory rheumatic diseases. 7, 4

• This is a "nociplastic" pain condition with dysfunction of neuro-circuits involving perception, transmission, and processing of nociceptive stimuli. 4

Common Diagnostic Pitfalls

• Do not rely solely on tender point examination in isolation—the widespread pain criterion and duration requirement are equally essential. 6

• Avoid dismissing the diagnosis due to psychiatric comorbidity—while mood disorders are common in fibromyalgia, they do not exclude the diagnosis but should be evaluated and addressed separately. 6

• Do not order extensive imaging or specialized testing unless specific red flags suggest alternative diagnoses (e.g., inflammatory arthritis, malignancy, infection). 3

Outcome Assessment Tools

• Use the Fibromyalgia Impact Questionnaire (FIQ) to assess functional impairment and treatment response, measuring physical function, work status, depression, anxiety, morning tiredness, pain, stiffness, fatigue, and well-being. 2

• Measure pain intensity using a visual analog scale (0-100 mm) or numeric rating scale (0-10) as the primary pain outcome measure. 2