Making a diagnosis
Fibromyalgia should be suspected in patients presenting with chronic (greater than 3 months), multifocal pain that cannot be explained by an obvious pathological process – e.g. inflammation, infection, degeneration or neoplasm. Once fibromyalgia is suspected, simple laboratory tests should be performed to exclude conditions that may present in the same way.
Differential diagnosis to consider in patients with fibromyalgia like pain:-
- Inflammatory rheumatic conditions
- Early rheumatoid arthritis
- Polymyalgia rheumatic
- Giant cell arteritis
- Systemic vasculitis
- Inflammatory spondyloarthritis
- Systemic lupus erythematosus
- Neuropathies (tend to be more localised)
- Multiple sclerosis (tend to have motor and sensory defects)
- Vitamin D deficiency
Laboratory tests should be tailored to the patient’s symptoms, however if a diagnosis of fibromyalgia is suspected the following would be considered a baseline set of investigations:-
- Full blood count
- Erythrocyte sedimentation rate
- C-reactive protein
- Thyroid function
- Creatine kinase
In 1990 the American College of Rheumatology (ACR) adopted research criteria as diagnostic criteria for fibromyalgia. These were superseded by the 2010 criteria. The new criteria take into account the fuller symptom complex of fibromyalgia and, although intended for epidemiological studies, are more applicable to the individual. The Canadian guideline recommends “The ACR 2010 diagnostic criteria for fibromyalgia can be used at initial assessment to validate a clinical diagnosis of fibromyalgia with the understanding that symptoms vary over time.”
A patient satisfies diagnostic criteria for fibromyalgia if all the following 3 conditions are met:
1) Widespread pain index (WPI) 7 and symptom severity (SS) scale score 5 or WPI 3–6 and SS scale score 9.
2) Symptoms have been present at a similar level for at least 3 months.
3) The patient does not have a disorder that would otherwise explain the pain.