Background/Purpose: The ACR 1990 diagnostic criteria for fibromyalgia includes a definition for chronic widespread pain (CWP) that depends on a particular distribution of pain sites. The new proposed ACR 2010 criteria instead has a Widespread Pain Index which takes into account the number of sites only. The purpose of this analysis was to see, amongst persons reporting multi-site pain, if the distribution of pain sites has any association with a number of potential risk markers after adjustment for the number of sites.

Methods: The MUSICIAN survey was a general population survey aimed at identifying people with CWP for an intervention study. A questionnaire was sent by post to adults registered at family doctors in two areas of the United Kingdom. Questions included age, gender, employment status, smoking behaviour, height, weight, and questions on pain included a manikin in 35 sections to indicate the location of the pain. Respondents were included in the analysis who indicated that they had between 3 and 16 areas of pain, and that the pain had lasted 3 months or more. (People with less than 3 sites could not meet the ACR 1990 definition of widespread pain, while most of those with more than 16 sites did). Participants were classed as having pain that was widespread or not according to the ACR 1990 criterion. A number of potential associations with having widespread pain were tested using logistic regression to provide odds ratios (OR) with 95% confidence intervals (CI). These models were then adjusted for number of pain sites to see if any associations with the distribution pattern remained after accounting for having pain in multiple areas.

Results:  14680 people responded to the questionnaire, of which 7536 reported some chronic pain (prevalence 51.3%). In those with chronic pain, the median number of pain sites was 5 (interquartile range 3 to 9), and the prevalence of pain that met the ACR 1990 criterion for being widespread was 32.1%. Included in the analysis were 5715 respondents with chronic pain in 3 to 16 areas, of which 2037 (35.6%) met the criterion for widespread pain. Gender age, smoking and employment status all had significant associations with ACR 1990 widespread pain (see table). After adjustment for number of pain sites most of these associations either became non-significant or were attenuated.

Conclusion: We have shown that when number of pain sites was taken into account, the particular distribution of sites did not continue to have significant relationships with many associated factors. This might indicate that is not so much that the pattern of pain locations that is important as the multiplicity of areas. This may have implications in conditions such as fibromyalgia where pain across multiple areas is involved. Based on this data, the use of a measure that looks at the number of pain sites rather than a particular distribution is acceptable as a diagnostic criterion.