Thermal Scanning Offers Promise of Early Arthritis Detection
DURHAM, N.C. – A device developed to scan computer circuit boards for defects can detect the earliest signs of hand osteoarthritis, researchers at Duke University Medical Center have found.
The thermal scanner, sensitive enough to detect differences of a tenth of a degree Fahrenheit revealed that the temperature of finger joints is proportional to the severity of osteoarthritis. The study showed that finger joints are warmer than average – a sign of inflammation -- in the first stage of osteoarthritis. In contrast, X-rays of fingers at this early stage of the disease produce inconclusive findings, said Virginia Kraus, M.D., a rheumatologist and associate professor of medicine at Duke University Medical Center.
The researchers' temperature scans also showed that as osteoarthritis symptoms increased in severity, the joints tended to cool. The researchers' analysis showed that the progressively cooler joint temperatures correlate with increasing disease severity revealed in X-rays of the same joints, Kraus said.
X-rays remains the standard clinical technique for diagnosing osteoarthritis, Kraus said. But thermal scanning holds promise for detecting osteoarthritis in the first stage of the disease, before joint changes become apparent on X-rays and before symptoms such as pain and joint enlargement appear, she said. "As we learn more about early stages of the disease, I think we'll be able to intervene earlier, when there will be more chance of making a difference," Kraus said.
The study was published in the July, 2004 issue of Rheumatology. Funding was provided by the National Institutes of Health.
Osteoarthritis results from the complex interaction among genetics, inflammation, mechanical forces and cellular and biochemical processes, Kraus said. The disease progresses through distinct stages visible with X-rays, including formation of bony spurs called osteophytes, progressive loss of joint space and joint erosion and remodeling. However, these X-ray changes occur relatively late in the process of osteoarthritis, which is one reason why joint symptoms of arthritis and X-rays often don't coincide, Kraus said
The Duke study examined 91 people with clinical hand osteoarthritis in both hands and a minimum of three joints with bony enlargements. The majority were women (80.2 percent) and most were right-handed (86 out of 91).
The researchers analyzed three joints on each finger, excluding thumbs, with the thermal scanner, resulting in 2,184 joint measurements. The conditions ranged from joints with no apparent arthritis to joints with the highest score on a radiographic scale for arthritis. About half of the study subjects took anti-inflammatory drugs called NSAIDS, but there was no apparent effect of NSAID use on joint surface temperature, found the researchers. NSAIDS, or non-steroidal anti-inflammatory drugs, include aspirin, ibuprofen and naproxen.
The researchers observed significant temperature differences between non-osteoarthritis and osteoarthritis-affected joints. The researchers relied on the Kellgren Lawrence grading system to categorize the joints by X-rays: grade KL0 is a normal joint, grade KL1 is a joint with a small bony growth, or osteophyte, of doubtful significance. The scale stops at KL4, which marks severe joint space narrowing and large osteophytes.
The study showed joints meeting the KL1 criteria were significantly warmer than KL0 joints, while KL2 through KL4 joints were colder than KL0 joints. These results support the idea that the earliest phase of hand osteoarthritis represents an inflammatory phase of the disease, Kraus said. However, the drop in temperature as the disease worsens is an enigma. "It's unclear if it's from disuse or lack of blood supply, but temperature somehow diminishes as bony enlargements grow," Kraus said.
The thermal scanner, loaned to Duke for the study, is used by computer manufacturers to detect defects in computer circuit boards, said Gabor Varju, M.D., lead author of the study and a pulmonary fellow at East Carolina University.
"Thermography was available in the 1970s and 1980s, but the technology was unreliable. The technology has improved to the point that we could do this study with reliable results," Varju said.
In the future, thermography could be used help evaluate the effectiveness of osteoarthritis treatments by checking for changes in joint temperature, he said.
Other authors include Carl Pieper, assistant professor of radiology at Duke University Medical Center, and Jordan Renner, professor of radiology and allied health sciences at the University of North Carolina, Chapel Hill.