To investigate the value of ultrasonography (US) for diagnosing synovitis associated with rheumatoid arthritis (RA).
Bilateral metacarpophalangeal (MCP), proximal interphalangeal (PIP) II-V and wrist joints of 46 RA patients and 35 healthy controls were evaluated by quantitative and semiquantitative US. Wrists on more severely affected sides of 20 of the 46 patients also underwent magnetic resonance imaging (MRI). The MRI and US results were compared. The US cutoff to distinguish pathology was calculated. The two US methods were compared and the correlation between quantitative methods and clinical serologic markers was analyzed.
The imaging techniques (US and MRI) for detecting synovitis produced consistent results (γ = 0.70-0.77, P < 0.001). When the cutoffs for the MCP and PIP joints were 2.5 and 2.6 mm, respectively; the sensitivities/specificities were 82.8%/85.8% and 98.2%/84.8%, respectively. When the cutoff for the wrist was 5.2 mm, the sensitivity/specificity was 93.4%/93.4%. The average synovial membrane thickness was positively related to biochemical markers erythrocyte sedimentation rate, C-reactive protein, anticyclic citrullinated peptide antibody, and Disease Activity Index of 28 joints (γ = 0.307-0.614; P = 0.020, 0.038, 0.01, < 0.001, respectively) but was poorly related to rheumatoid factor immunoglobulin A (RF-IgA), RF-IgM, and RF-IgG (γ = 0.06-0.115; P = 0.45, 0.45, 0.62, respectively).
US is a valid method for diagnosing early-stage synovitis, with high-accuracy cutoffs for MCP, PIP and wrist joints set at 2.5, 2.6 and 5.2 mm. The mean synovial thicknesses of the bilateral wrist, MCP II-IV and PIP II-IV joints can be used to assess disease activity.