Background/Purpose : The 2010 American College of Rheumatology (ACR) preliminary criteria for the diagnosis of fibromyalgia (FM2010) and its extension for clinical research by patient self-report questionnaire (FM2011) broke with previous 1990 criteria (ACR1990) by eliminating tender points, but also by eliminating the requirement that pain be widespread (4 quadrant + axial) (WSP). By changing the definition of fibromyalgia (FM), the 2010 and 2011 criteria created an expected and natural discordance with the 1990 criteria. In addition, some researchers indicated that elimination of WSP could lead to misclassification by including cases that did not have generalized pain (ACR1990 regions = 5) into the FM definition; and thereby introducing bias favoring psychological symptoms. In the ACR 2010 criteria paper, WSP was absent in 6%-7% of those with FM.

Methods:  From 17,385 mixed rheumatic disease patients, we studied 4,964 (28.6%) who satisfied FM2011 criteria, and we evaluated the presence of WSP, and widespread pain index (WPI) scores (0-19) and the Symptom severity scales (SSS) (0-12). FM is diagnosed when (WPI ≥7 AND SS ≥5) OR (WPI 3–6 AND SS ≥9). We also calculated the number of painful regions (0-5: 4 quadrants + axial) from ACR1990. We determined the proportion of patients meeting FM2011 criteria who did not meet the ACR1990 widespread pain definition

Results: Among patients FM2011 (+) 6.6% did not have WSP. 3.5% those FM2011 (+) who had WPI <7did not have WSP.  As shown in Table 1, 93.4% of FM2011 (+) had 5 ACR1990 painful regions; 5,3% had 4, and only 1.3% had <4. For the 0-19 WPI, 7% had scores between 4 and 6. Overall, those not meeting the ACR1990 definition, and those perhaps appropriately (regions = 4) not meeting the criteria, were few. 

Conclusion:   FM criteria may be used 1) for differential diagnosis in which fibromyalgia is the best clinical diagnosis to explain a patient’s symptoms; or 2) for concomitant diagnosis in which the several illness are identified, one of which is fibromyalgia. FM2010 and FM2011 were designed for optimal diagnosis in the setting of usual rheumatic disease presentation and usual clinic prevalence. When used in settings where non-WSP and regional or psychiatric diagnoses are substantially increased, FM criteria will “misclassify” persons. This occurs because there is no reliable gold standard fibromyalgia definition. The solution to this type of misclassification is to use the most appropriate clinical diagnosis (e.g., regional arm pain or rheumatoid arthritis) and indicate the patient also satisfied fibromyalgia criteria. In a general or rheumatic disease clinic setting few people will meet FM2011 criteria without WSP, but most will also have many painful regions.

Table 1. Relation between Widespread Pain index and Widespread Pain Regions (ACR1990) and Fibromyalgia Criteria Status

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/when-fibromyalgia-criteria-misclassify/