Is all chronic pain the same? A 25-year follow-up study

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Abstract
Many apparently distinctive clinical syndromes of pain and dysfunction show considerable overlap in both population and clinical settings. If the explanation is that they all share a common underlying mechanism, then we hypothesize that any one syndrome will be unlikely to retain its distinctiveness over time. Consultation data from general practice records for 10,073 women, collected between 1968 and 1978, was linked with information on pain complaints obtained from a subsequent postal survey carried out in 1994. Illness episodes were identified from the general practice records and grouped into diagnostic subcategories. Associations between these and future pain complaints were explored, adjusting for age, smoking, body mass index and social class in a series of nested case–control analyses. Overall, the strongest independent associations of current pain were with episodes of musculoskeletal illness and mental disorders recorded 15–25 years earlier; these associations were more marked for widespread pain (odds ratios 1.8 and 1.7, respectively) than for non-widespread pain (ORs 1.3 and 1.2, respectively). In analyses of specific illness subcategories, the strongest links for head and neck pain were with earlier migraine. Back pain was most strongly associated with earlier back complaints, and abdominal pain with earlier intestinal-related problems. By contrast, chest pain was most strongly linked with earlier psychological illness. Earlier soft tissue illness episodes showed no distinctive patterns of associations over time with subsequent regional pain complaints. This analysis provides some support for shared mechanisms of chronicity across regional pain complaints, particularly in relation to the earlier occurrence of mental illness and the development of widespread pain. However, there is strong evidence that regional pain complaints also track distinctively over time. This argues against chronic functional and pain syndromes all being the same problem with a common mechanism of persistence, and in favor of unique regional influences on chronicity as well.