To optimize use of the Disease Activity Score in 28 joints (DAS28) in early rheumatoid arthritis (RA) by adding the "squeeze test" of forefeet.
The squeeze test is used to examine bilateral compression pain (BCP) across the metatarsophalangeal (MTP) joints. For this study, data for patients participating in the Treatment in the Rotterdam Early Arthritis Cohort study, an ongoing clinical trial that evaluates different induction therapies in patients with early RA, were randomly divided into 2 subsets. In subset 1 (149 patients and 819 disease activity assessments), the mathematical function of the DAS28-squeeze was constructed using a linear regression model with the DAS as the dependent variable and the DAS28 and squeeze test as the independent variables. A DAS28-BCP disease state was also constructed, in which DAS28 disease state categorizations were upgraded one state if the result of the squeeze test was positive. In subset 2 (153 patients and 754 assessments), concordance in disease states between the DAS28, DAS28-squeeze, and DAS28-BCP disease states was compared, using both the DAS and Boolean-defined remission criteria as reference.
Agreement between the DAS and the DAS28-squeeze (82%) was significantly higher than agreement between the DAS and the DAS28 (76%). When we assessed the group of patients who had arthritis of the forefeet only (22 patients and 46 assessments), overall agreement between the DAS and the DAS28 was 40%, while agreement between the DAS and the DAS28-squeeze was 59% and that between the DAS and the DAS28-BCP disease state was 65%. Furthermore, the specificities of the DAS28-squeeze and the DAS28-BCP (80% and 81%, respectively) were higher than that of the DAS28 (76%), while the sensitivities of the DAS28, DAS28-squeeze, and DAS28-BCP to identify true remission according to the Boolean criteria were 88%, 87%, and 81%, respectively.
Adding the squeeze test of forefeet to the DAS28 has value for dependably classifying the disease state in patients with early RA.