CHAPEL HILL -- When older people complain of joint pain but hard evidence of its cause cannot be found, doctors and others may say -- or at least think -- "it's all in their heads." But now scientists say that's not necessarily so.
Medical researchers at the University of North Carolina at Chapel Hill have discovered that a naturally occurring protein known as COMP significantly increases in the blood of people with hip or knee osteoarthritis even before X-rays reveal joint damage.
The findings could become increasingly important, the scientists say, as the number of Americans suffering from the painful degenerative condition swells from 40 million people to 60 million by 2020. With more research, a clinically useful osteoarthritis screening test measuring COMP could be developed.
"This work shows that there may be a way to identify osteoarthritis early," said lead investigator Dr. Joanne Jordan, research associate professor of medicine at the UNC-CH School of Medicine. "It also shows that doctors shouldn't just dismiss patients complaining of joint pain as being complainers or being depressed. If those patients have elevated levels of COMP, which is short for cartilage oligomeric matrix protein, then something really is going on with them that we may need to know about and possibly treat."
The study, to be described at an American College of Rheumatology meeting in Philadelphia Monday (Oct. 30), involved 145 of 3,200 randomly selected people participating in the Johnston County Osteoarthritis Project, a large, government-sponsored N.C. study that for the first time includes many black subjects.
Previous research, especially at UNC-CH but also elsewhere, showed that higher levels of COMP, which also is found in cartilage, tendons and joints, are associated with osteoarthritis, Jordan said. The new work concentrated on people with no X-ray evidence of osteoarthritis.
"We wanted to see if we could find differences in COMP levels in people whose X-rays were negative so we studied a sub-sample of participants with no osteoarthritis evident in X-rays of either their knees or their hips," she said. "When we compared those levels with whether they said they suffered joint pain, we found that COMP corresponded strongly with reports of pain."
People with five or more years of hip or knee pain, for example, showed about 33 percent more of the protein in their blood than did people reporting no pain, Jordan said.
Controlling statistically for age, sex and other variables did not change the outcome. The clear association between elevated COMP and joint pain remained. The protein also was elevated in participants who had early abnormal findings or pain in their knees or hips during physical examinations.
Jordan is a member of the Thurston Arthritis Research Center at UNC-CH's School of Medicine. Anca Dragomir, an epidemiology doctoral student in the UNC-CH School of Public Health, presented the findings. Others involved in the study were Dr. Virginia B. Kraus, a Duke University rheumatologist, and Dr. Jordan Renner, associate professor of radiology, and Gheorghe Luta, a biostatistics doctoral student, both at UNC-CH.
Half the overall study group was white and the other half black, but scientists presented findings limited to whites because the two races differ somewhat in their experiences with osteoarthritis. A similar analysis exclusively with black subjects currently is under way. Half the participants were women.
When the continuing research began, participants were age 45 or older. About 40 percent of those included in the COMP study reported significant joint pain.
"The best things people can do to minimize knee and hip osteoarthritis are to avoid activities that put heavy physical demands on joints and especially to lose any excess weight," Jordan said. "Also, evidence suggests it's important to keep thigh and other leg muscles strong through non-stressful exercise."
The Centers for Disease Control and Prevention, the National Institute of Arthritis, Musculoskeletal and Skin Diseases and the Arthritis Foundation support the continuing research.
Note: Jordan can be reached at (919) 383-0861 until mid-Friday afternoon, Oct. 27. Beginning Friday evening, she can be reached at the American College of Rheumatology meeting at the Philadelphia Marriott at (215) 625-2900. She will check her messages periodically and respond promptly to reporters. After the meeting, she can be reached at her office at (919) 966-0559.
Contact: David Williamson, (919) 962-8596.