Background Power Doppler ultrasonography (PdUS) is widely used for the evaluation of the entheses in spondylarthritis (SpA). PdUS has been shown to be useful for the diagnosis and the evaluation of the disease activity. However, it can be time-consuming and its intra and interobserver reproducibility depends on the experience of the sonographer. Three-dimensional (3D) US has already demonstrated a good reliability and operator independency in the evaluation of rheumatoid arthritis wrist and reduces the time needed to perform this examination (1).

Objectives The aim of this study was to compare the reliability of 3D and conventional two-dimensional (2D) US in the scoring of enthesitis in SpA.

Methods Sixteen patients with SpA according to ASAS criteria were included. The readers were 2 rheumatologists, one experimented in musculoskeletal US (reader 1) and one beginner (reader 2) (respectively mean experience 6 years and 6 months). They performed independently a 2D US scoring of the entheses using the MASEI score followed by a 3D acquisition of the same entheseal sites. The assessment of the 3D US was performed a minimum of 1 week apart using the images stored on the US unit. Intra-observer reliability was evaluated by a second reading of the same images. The duration of 2D US scanning, 3D US acquisition and reading was recorded. The quality of 3D US acquisitions was scored between 0 and 3. For the reliability analysis, we used the two-way, mixed-effect model (absolute agreement) single-measure intraclass correlation coefficients (ICCs)and results are given with 95% confidence interval (CI).

Results They were 12 men and 4 women, mean age 45.7 years (range 26-70) and mean disease duration 11 years (0-33). The mean ASDAS was 2.4 (0.4-5.8). The mean MASEI score was 10 (+/-7). Intra-observer reproductibility was good to excellent for 2D US and good for 3D US (ICC (95%CI) 2D US: 0.776 (0.471-0.916) and 0.96 (0.892-0.986) and ICC (95%CI) 3D US: 0.796 (0.498-0.921) and 0.703 (0.325-0.886) for reader 1 and 2 respectively). Inter-observer reliability was slightly better for 3D US than for 2D US (ICC (95%CI) 0.776 (0.471-0.916) for 3D US versus 0.641 (0.221-0.859) for 2D US). Finally a good correlation was found between 2D and 3D US (ICC (95%CI) 0.705 (0.329-0.887) for reader 1 and 0.756 (0.444-0.906) for reader 2). The mean time (+/-SD) for 2D US scanning was 23 minutes (+/-4) whereas the mean time for 3D US volume acquisition and reading was 16.5 min (+/-2.6) (p<0.001) (with a mean 7.3 min (+/-0.9) for the acquisition and a mean 9.2 minutes (+/-2.2) for the review of the images). The mean score (+/-SD) for quality of 3D US acquisitions was 2.4 (+/0.1)/3 with no significant difference between the entheseal sites.

Conclusions This study demonstrates a good intra and interobserver reliability of 3D US assessment of enthesitis in SpA. We also found a good correlation between the 2D US and 3D US scoring. It can be performed by a non-experimented examiner without loss of reliability. Finally, 3D US significantly shortened the time of scanning.

References

1. Filipucci et al. Ultrasound imaging for the rheumatologist. Sonographic assessment of hand and wrist joint involvement in rheumatoid arthritis : comparison between two- and three-dimensional ultrasonography. Clin Exp Rheumatol 2009;27:197-200.

References

Disclosure of Interest None Declared