To explore development of a screening test for rheumatoid arthritis (RA) patients most likely to develop radiographic damage in the next year. The test is a simple, objective measurement of elevated dermal temperature over an inflamed joint in this observational, prospective cohort study.
Seropositive RA patients were sequentially enrolled into cohorts with hot or cool joints, as determined by a dermal thermometer. Patients naive to biologic therapy were maintained on a stable dosage of methotrexate (20-25 mg/week). The hot-joint cohort had a joint skin temperature greater than their body temperature on vital signs. Hand/wrist radiographs obtained at baseline and 1 year later were read and scored using modified Sharp/van der Heijde scores (SHS) by a single reader without sequence order or identifiers.
Each cohort consisted of 104 patients enrolled into observation between 2009 and 2014. Patients in the cohort with hot joints had a mean ± SD joint temperature of 1.06 ± 0.69°F above central body temperature and a nearly 4-fold higher risk of new radiographic damage than those with cool joints (SHS score 8.7 ± 6.2 versus 2.5 ± 1.4; P < 0.001). Sensitivity and specificity for joint temperature to predict radiographic damage in the next year were 92% and 78%, respectively, in the hot-joint cohort. As expected, this cohort at baseline was younger, had more recent onset RA, and had higher Westergren erythrocyte sedimentation rate levels than the cool-joint cohort (P < 0.001 for each).
Dermal joint temperature may become a screening test to quickly and accurately identify individual RA patients at high risk for radiographic damage and those who may benefit most from biologic therapy.