Using different measurements of rheumatoid arthritis activity to work out underlying causes of pain

What is it about?

Background People with rheumatoid arthritis (RA) usually have unpleasant and unacceptable pain levels, even when their condition is being well-managed by their rheumatologist. This has lead researchers to look for novel causes of pain, instead of inflammation. When people have RA, they are often examined by a doctor or nurse who will look at (1) swelling of the joints, (2) tenderness of the joints, (3) ask the person’s own opinion about their wellbeing, and (4) take a blood measurement. These measurements are used to make a score called DAS28. The DAS28 score is very important for decision-making in people with RA. For example, it is often used to decide the type of drugs that will be used. Two of the four parts of the DAS28 directly measure inflammation; they are the joint swelling and the blood measurement. Although the joint tenderness and the feelings of wellbeing are also partly related to inflammation, they are also strongly influenced by pain sensations and pain sensitivity. People with RA can become especially sensitive to pain (sometimes being told that they also have fibromyalgia). These people can have worse joint tenderness and feel less well, even despite having mild levels of inflammation. Aim We aimed to look at comparing the pain-related and the inflammation measures that are used to make DAS28. We wanted to see whether they could be used in a different way that would measure the sensitivity to pain. How the study was carried out We found that the DAS28 was related to pain, but that this was probably due to its measurement of inflammation. We then looked at 3 different ways of analysing the four DAS28 measurements. We found that these different methods could be used to investigate causes of pain that were not related to inflammation. Counting tender joints and swollen joints seemed to be the easiest and most informative way of analysing the data. The group of people with many more tender joints than swollen joints were more likely to experience worse pain, be more sensitive to painful tests, and experience worse pain in the next year. Having more tender joints than swollen joints was also associated with fibromyalgia in RA. The study used data collected from different research studies of people with RA. They were the Early RA Network (ERAN), the British Society for Rheumatology Biologics Register (BSRBR), a study of pain sensitivity in 50 people with RA, and measurements from teaching sessions for DAS28 scoring.

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Why is it important?

This study adds to our evidence that different pain mechanisms can make important contributions to arthritis pain. When inflammation is not causing pain, the person may need to be treated differently.

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