Background/Purpose: Chronic widespread pain (CWP) is often used as a surrogate for fibromyalgia in epidemiological research, particularly in Europe and in whiplash-related injuries. This CWP substitution occurred because it was operationally impossible to perform tender point examinations in epidemiological and survey research. CWP is a requirement for fibromyalgia diagnosis when the American College of Rheumatology (ACR) 1990 criteria are used. 20-35% of patients with CWP will also satisfy fibromyalgia criteria. Despite the common use of CWP, it is not clear how closely CWP positive patients resemble those with fibromyalgia, and whether CWP is a valid substitution for fibromyalgia. In this report we determined the relative severity of patients satisfying the CWP and fibromyalgia criteria.

Methods : We studied 6,583 rheumatic disease patients who completed a research questionnaire that contained assessments of criteria and severity variables. Fibromyalgia was diagnosed using the 2010 American College of Rheumatology (ACR) criteria for fibromyalgia, as modified for survey research. Widespread pain used the 1990 ACR definition: pain above and below the waist, on the left and right sides of the body, and involving the axial skeleton. Severity measures included the Polysymptomatic Distress Scale (PSD) and the Symptom Severity (SS) scale from the 2010 criteria. In addition, we employed other standard assessments of severity, including measures of pain, sleep, fatigue and quality of life. We categorized patients as a) without CWP, b) with fibromyalgia, c) with CWP assuming 20% of CWP cases had FM, and d) with CWP assuming 33% of CWP cases had fibromyalgia (Table 1).

Results : Figure 1 shows the relation of both measures to PSD in the overall sample.  X and y lines cross when probability of diagnosis is >= 0.5. This occurs at 9.3 and 13.3 on the PSD scale for CWP and FM, respectively. Table 1, adjusted for age and sex, demonstrates that patients with fibromyalgia have more severe symptoms than those with CWP at 20% and 33% prevalence levels. For the 3 clinical VAS scales, fibromyalgia patients are approximately 30% more severe than those with CWP.

Conclusion: Patients satisfying fibromyalgia criteria have a more severe illness than those with CWP. The use of CWP as a surrogate measure of fibromyalgia substantially underestimates fibromyalgia severity, but still identifies a group of severe patients.

Table 1. Severity status of patients with fibromyalgia or chronic widespread pain