Ultrasound (US) examination can visualise and clarify involved joints anatomically in patients with rheumatoid arthritis (RA), and it enables physicians to verify the accuracy of clinical assessments of involved joints. Here, we studied the practical 'miscount'- calculated by subtracting US-determined involved joint count from clinically determined involved joint count - and analysed possible contributing factors for increased miscount.
The study population consisted of 137 patients with RA. Physical joint examination was performed by 3 assessors with different levels of experience in rheumatology, followed by US joint examination. Clinical and US examinations were performed on 28 joints (proximal interphalangeal, metacarpophalangeal, wrist, elbow, shoulder, and knee on both sides). Miscount was calculated for all patients, and multivariate analysis was conducted on possible contributing factors for miscount, including age, sex, body mass index, disease duration, Steinbrocker stage, erythrocyte sedimentation rate (ESR), C-reactive protein level, patient global assessment (GA), evaluator GA, matrix metalloproteinase-3 level, and power Doppler (PD) score.
A high variability in concordance rate among the joint sites was observed among the 3 assessors. The average miscount was 1.07 (SD, 5.19; range, 18 to -11). ESR and patient GA were determined as significant contributing factors for false-positive miscount, whereas PD score and age were significant factors for false-negative miscount.
In addition to the condition of the involved joint distribution and the assessor's clinical examination skills, the patients' background can also lead to increased miscount. Assessors should be blinded to patients' background information, and US complementation should be included in usual clinical joint examinations.