Power Doppler (PD) and gray scale (GS) imaging are commonly employed during ultrasonography in rheumatoid arthritis (RA). While PD vascularity is often regarded as an ultrasound feature of more active joint inflammation, the true clinical significance of GS joint inflammation is less understood. We aimed to gain further insight into ultrasound PD and GS joint inflammation by studying their association with Disease Activity Score of 28 joints (DAS28) (a disease activity measure) and ultrasound-detected bone erosion (a structural damage measure).
In this cross-sectional study, ultrasound PD and GS joint inflammation were graded 0-3 (semi-quantitatively) and bone erosion was graded as yes = 1/no = 0 at each joint recess. Linear regression and Pearson correlation were used to characterize relationships and assess correlation of PD and GS scores with DAS28 and ultrasound erosion scores.
One thousand and eighty joints and 1800 joint recesses from 36 peripheral joint sites (bilateral metacarpophalangeal joints, thumb interphalangeal joints, proximal interphalangeal joints, metatarsophalangeal joints, elbow, wrist and ankle) were scanned in 30 adult RA patients. PD scores correlated with DAS28 (r = 0.46, P = 0.0104) but not with ultrasound erosion scores; GS scores correlated with ultrasound erosion (r = 0.64, P = 0.0001) but not with DAS28 scores. Simple linear regression revealed PD as predictive of DAS28 (P = 0.0104) and GS as predictive of ultrasound-detected bone erosion (P = 0.0001).
Ultrasound PD joint inflammation is associated with disease activity and is correlated with DAS28. In contrast, GS joint inflammation is associated with structural damage and is correlated with ultrasound-detected bone erosion.