People with rheumatoid arthritis (RA) have lower thresholds for pain and may have deficits in a central nervous system (CNS) mechanism that helps to modulate how the body experiences pain, according to recent research funded by the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the NIH, and published in the journal Arthritis and Rheumatism. In addition, sleep disruptions, which are common among people with RA, may exacerbate pain sensitivity.
Although RA pain is frequently attributed to joint inflammation, RA patients often report lingering discomfort even when the inflammation is controlled. "Researchers have theorized that CNS regulation of pain may be altered in those with RA, which would help explain why they continue to feel pain after inflammation is suppressed," said lead study author Yvonne C. Lee, M.D., of Brigham and Women’s Hospital.
RA patients and others with chronically painful conditions such as fibromyalgia may have impaired conditioned pain modulation (CPM), a process by which the CNS regulates pain that is coming from multiple sources or sites. "CPM is the so-called ‘pain inhibits pain’ mechanism," Dr. Lee noted. "It can be a measure of central pain processing, but it has not been adequately examined in people with RA."
In this study, Dr. Lee and colleagues recruited 58 women with RA age 40 and over, and 54 healthy women of similar ages as a comparison group. The researchers determined the point at which the women first felt pain when pressure was exerted at both joint and non-joint sites (pressure-pain threshold). They also measured the point at which the pressure caused unbearable pain (pressure-pain tolerance). In addition, the researchers assessed CPM by measuring pressure-pain threshold right before participants immersed their hand in ice cold water, and 20 seconds into the cold-water bath.
Results showed that the women with RA were more sensitive to pressure-pain at joint sites compared to those without RA, suggesting that their CPM process is impaired. RA patients also had more sleep problems compared to the healthy women, and sleep disturbances were associated with reduced CPM. In addition, the women with RA had higher rates of anxiety and depression, and were more likely to have negative emotions and thoughts in response to pain (e.g., pain catastrophizing).
The study suggests that RA patients’ pain regulation process may be abnormal. The data provide evidence that some pain may be more deeply rooted in CNS processing mechanisms, rather than in inflamed joints. In addition, the research supports other work showing that sleep disruptions may increase a person’s likelihood of experiencing enhanced sensitivity to pain.
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Lee YC, Lu B, Edwards RR, Wasan AD, Nassikas NJ, Clauw DJ, Solomon DH, Karlson EW. The role of sleep problems in central pain processing in rheumatoid arthritis. Arthritis Rheum. Jan 2013. 65(1):59-68. PMID: 23124650
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