Chronic Widespread Pain (CWP)

A total of 99 female twin pairs (198 women) participated in this study to understand more about the causes and conditions associated with chronic widespread pain. This study examined perceptions of pain, factors related to sleep, hormones related to the body’s response to stress, and inflammatory markers that might affect sensitivity to pain. A twin study was done because one of the aims of the study was to discover if familial or environmental factors have a role in chronic pain.

At home, twin participants collected saliva for 7 days, kept a daily diary of sleep, stress, mood and pain levels, and completed many questionnaires. They then came to the University of Washington Medical Center for two days. They had a physical exam, did exercise and pain sensitivity tests, and wore a Holter monitor.

One of the pain sensitivity tests was the cold pressor test. Each twin was asked to put her hand and forearm into a container of ice water kept at just above freezing. She was asked to say when the sensation changed from cold to pain (her pain threshold). She could remove her arm from the water when she could no longer stand the pain (her pain tolerance). She was asked to rate her pain at several points in the procedure.

C-Reactive Protein (CRP) was one of several inflammatory markers in blood that was measured. CRP is a general indicator of inflammation in the body. The higher the CRP, the more inflammation the person has.

An important finding of this study is that there is a link between blood levels of CRP and cold pain sensitivity. Higher levels of CRP were associated with higher pain ratings at pain threshold and pain tolerance. The twin analysis showed that this link may be partly due to non-shared environmental factors, and is not much influenced by shared familial factors.

These results mean that that in the future, your doctor might be able to predict if you are at risk for certain chronic pain conditions by doing a simple blood test for CRP or by performing a simple pain sensitivity test. This would allow earlier diagnosis and treatment of these chronic pain conditions. Also, since non-shared environmental factors appear to be more important than shared familial factors, more research can be targeted to identify which environmental factors are related to chronic pain conditions.