Background It is recommended that a joint be classified as clinically swollen if this swelling is beyond doubt. However in clinical practice the evaluation of joint swelling in patients with rheumatoid arthritis (RA) is often hindered by joint deformity, secondary osteoarthritis (OA) or adiposity.
Objectives The aim of this study was to evaluate the ambiguity and reliability of clinical swollen joint assessment in patients with RA.
Methods Clinical joint swelling was evaluated in 2 cohorts of consecutive RA patients with at least 1 swollen joint. In Cohort A (n=20) a conventional 28 swollen joint count (SJC) was performed on the same day by two independent, blinded examiners. In Cohort B (n=34) two independent, blinded examiners performed a modified 28 SJC in which they graded the joints as either definitely swollen, non-swollen and doubtfully swollen, the latter defined as a state in which the examiner was unable to exclude or confirm joint swelling due to limited evaluation attributed to the physical characteristics of the joint. In addition a standard grey-scale (GS) and Power Doppler (PD) sonographic evaluation was performed by a sonographer blinded to clinical data in Cohort B patients. Presence/absence of GS synovitis, PD signal, erosion and osteophytes were recorded. Osteophytes were also evaluated on conventional anterior-posterior radiographs of the hands.
Results A total of 1512 joints were clinically evaluated in 54 RA patients in 2 cohorts. Ninety-one percent (31/34) of patients in Cohort B had at least one doubtfully swollen joint, with a maximum number of 4 doubtful joints per patient. The top 5 joints, which were found to be doubtfully swollen by at least one examiner were the wrist, MCP3, MCP2, knee, and PIP2 joints. Interobserver reliability, evaluated by intraclass correlation coefficient (ICC) in Cohort A for the conventional SJC and in Cohort B for the modified SJC was 0.80 (95% confidence interval (95%CI) 0.77-0.83) and 0.82 (95%CI: 0.79-0.84) respectively. Agreement between the 2 examiners for definitely swollen and doubtfully swollen joints was 62% and 26% respectively. Doubtfully swollen joints were more often GS (p<0.001) and PD (p<0.001) positive as compared to non-swollen joints (83% vs. 51% and 28% vs. 11% respectively) and had more frequently osteophytes on ultrasound than either swollen (p=0.010) or non-swollen joints (p=0.006) (22% vs. 8%/11% respectively) (Table 1). Osteophytes detected on conventional radiography were also more frequent in doubtfully swollen joints in comparison to non-swollen or swollen joints (17% vs. 11.3%/7.5%). Erosions were slightly more commonly in swollen joints than in doubtfully swollen or non-swollen joints (3.7% vs. 2.8/2.4%). No association was found between body mass index and the number of doubtfully swollen joints.
Conclusions A modified SJC including doubtfully swollen joints is characterized by similar interobserver reliability as the conventional SJC. Agreement between two blinded examiners was however low for the evaluation of doubtful swelling. Doubtfully swollen joints more frequently had osteophytes on ultrasound as well as on conventional radiography suggesting a relationship between ambiguity of swelling and secondary OA in patients with RA.
Disclosure of Interest None declared