Clinical evaluation of optical spectral transmission imaging for detection of disease activity in rheumatoid arthritis

Objective: To investigate the performance and factors of influence of optical spectral transmission (OST) imaging as a new technique for measuring joint inflammation in rheumatoid arthritis (RA). Method: OST was performed in 24 RA patients and 37 controls. Mann–Whitney U-test was used to assess differences in OST score between RA patients and controls. Receiver operating characteristics (ROC), linear regression and generalized estimating equations analysis were used to assess the discriminative capability of OST and the association of OST score with clinical disease parameters, ultrasound, radiographic features and cardiovascular risk parameters. Results: Median OST score was higher in RA patients than in controls [16.9 (interquartile range 12.77–19.7) vs 12.11 (10.32–14.93)]. At patient level, OST score was moderately associated with ultrasound [beta 0.38 (95% CI 0.16–0.60), p = 0.001] and clinical disease activity [28-joint Disease Activity Score–C-reactive protein beta 0.30 (95% CI 0.04– 0.57), p = 0.024] in RA patients. In controls, male sex, high body mass index, and hypertension were associated with higher OST scores, while these associations were absent in RA. At joint level, the area under the ROC curve for OST score, with ultrasound or clinical swelling as reference, ranged from 0.63 to 0.70. Joint-space narrowing and malalignment were associated with higher OST joint scores, and subchondral sclerosis with lower scores.  Conclusion: OST provides an objective measure of synovitis and correlates moderately with other examined disease activity assessment tools. Clinical patient characteristics must be considered when interpreting the results.