Looking beyond inflammation: How the CAP questionnaire helps explain pain in rheumatoid arthritis
Full reference: Stephanie Louise Smith, Vasileios Georgopoulos, Onosi Sylvia Ifesemen, Richard James, Eamonn Ferguson, Richard J Wakefield, Deborah Wilson, Philip Buckley, Dorothy Platts, Susan Ledbury, Ernest Choy, Tim Pickles, Zoe Rutter-Locher, Bruce Kirkham, David Andrew Walsh, Daniel F McWilliams, Validity and contributions to pain from the central aspects of pain questionnaire in rheumatoid arthritis, Pain Rep. 2025 Jun 20;10(4):e1295. doi: 10.1097/PR9.0000000000001295
Rheumatoid arthritis (RA) is an inflammatory condition affecting the joints, often causing pain, stiffness, and swelling. Although treatments have significantly improved, many individuals still experience persistent pain. This study examined whether the Central Aspects of Pain (CAP) questionnaire, which evaluates how the brain and spinal cord (central nervous system) might amplify pain, can be used to assess people with RA and whether pain in RA could also originate from the central nervous system rather than solely from inflammation.
Researchers used the CAP questionnaire, originally developed for knee pain, to see if it could help understand pain in people with RA. The CAP questionnaire includes eight short questions about symptoms such as fatigue, poor sleep, anxiety, depression, and widespread pain. These symptoms are often observed in people experiencing what is known as nociplastic pain, pain that arises from altered pain processing in the central nervous system rather than changes in the joint.
Over 380 people with RA completed the CAP questionnaire and rated their pain. Some also underwent detailed tests, including blood tests and assessments of their sensitivity to stimuli such as pressure.
The study found that the CAP questionnaire was reliable and valid for use in RA. It was strongly linked to how much pain people reported, more than markers of inflammation like swelling or markers in the blood. In fact, the CAP score alone explained over a third of people’s reported pain. When combined with inflammation and other factors like age and sex, it explained 42% of pain severity.
Interestingly, although CAP was linked to how people felt, it was not associated with physical measures of pain sensitivity. This suggests that CAP might be capturing how the brain and emotions influence pain, sometimes referred to as psychological hypervigilance, rather than physical pain sensitivity alone.
In summary, this study demonstrates that the CAP questionnaire is appropriate for use in individuals with RA and that pain is not solely caused by inflammation. Central nervous system processing, including emotional and psychological factors, plays a significant role. The CAP questionnaire could be a valuable tool for healthcare providers to gain a more complete understanding of pain in RA and to support personalised treatment beyond merely managing inflammation.