Optical imaging compared to clinical examination in 484 rheumatoid arthritis patients: the Leeuwarden Handscan Registry

The Handscan is a novel objective optical imaging device for disease follow-up and management in rheumatoid arthritis patients. We aim to examine the association between the baseline outcomes of the Handscan, disease activity levels and joint swelling. The Handscan measures differences in laser light absorption between joints of fingers and wrists and adjacent reference tissue, indicating the presence or absence of inflammation. The device gives an optical spectral transmission (OST) index per joint. The average of these indices is represented in the total optical score (TOS). Associations between TOS and DAS28 at subject level and OST and swelling at joint level were examined. 484 RA patients were included. Compared to patients with high disease activity (defined by DAS28), TOS was significantly lower in patients with moderate (estimated coefficient B: − 7.09, P < 0.001), low disease activity (B: − 6.99, P < 0.001) and patients in remission (B: − 7.72, P < 0.001) but could not distinguish between the latter three disease states. TOS was significantly lower in females (B: − 3.2, P < 0.001). OST was significantly higher in swollen than non-swollen joints (B: 0.28, P < 0.001). TOS was significantly higher in patients with high disease activity than in those in remission or with low and moderate disease activity. The difference in TOS between males and females should be accounted for in the interpretation of this outcome. The OST at joint level discriminates swollen from non-swollen joints and could be a more promising tool than the overall optical activity reflected in TOS.