Abstract
Chronic pain has been traditionally defined by pain duration, but this approach has limited empirical support and does not account for chronic pain's multi-dimensionality. This study compared duration-based and prospective approaches to defining chronic pain in terms of their ability to predict future pain course and outcomes for primary care patients with three common pain conditions: back pain (n=971), headache (n=1078), or orofacial pain (n=455). At baseline, their chronic pain was classified retrospectively based on Pain Days in the prior six months and prospectively with a prognostic Risk Score identifying patients with "possible" or "probable" chronic pain. The 0-28 Risk Score was based on pain intensity, pain-related activity limitations, depressive symptoms, number of pain sites, and Pain Days. Pain and behavioral outcomes were assessed at six-month follow-up, and long-term opioid use was assessed two to five years after baseline. Risk Score consistently predicted clinically significant pain at six months better than did Pain Days alone (area under the curve of 0.74-0.78 for Risk Score vs. 0.63-0.73 for Pain Days). Risk Score was a stronger predictor of future SF-36 Physical Function, pain-related worry, unemployment, and long-term opioid use than Pain Days alone. Thus, for these three common pain conditions, a prognostic Risk Score had better predictive validity for pain outcomes than did pain duration alone. However, chronic pain appears to be a continuum rather than a distinct class, because long-term pain outcomes are highly variable and inherently uncertain.