Diagnostic Value of Optical Spectral Transmission in Rheumatoid Arthritis: Associations with Clinical Characteristics and Comparison with Joint Ultrasonography.

Objective: To examine the value of optical spectral transmission (OST) in detecting joint inflammation in patients with rheumatoid arthritis (RA) and to evaluate whether OST correlates with certain patient characteristics.

Methods: OST measurements were performed in the metacarpophalangeal, proximal intraphalangeal, and wrist joints of 168 patients with RA and 114 controls. OST difference between the 2 groups was statistically examined and subsequently controlled for the effect of possible confounding factors. Diagnostic OST performance was tested by receiver-operating characteristics. Moreover, associations of OST with clinical and serological activity markers (patient group), joint ultrasound (US; patient subgroup) and various anthropometric and epidemiologic parameters (patient and control group) were evaluated by Spearman correlation coefficient and a generalized linear statistical adjustment model.

Results: OST was significantly higher in the RA group than in the control group, even after adjustment for confounding factors (1.89; 95% CI 0.709-3.070, p = 0.002). Taking US as a reference, area under the curve for all 1251 joints simultaneously was 0.67 (95% CI 0.631-0.709). In the patient group, correlation and adjustment analyses showed associations of OST with various disease activity markers [28-joint count Disease Activity Score (rho 0.313), swollen joint counts (rho 0.361), C-reactive protein (rho 0.389); all, p = 0.001], age (rho 0.276, p < 0.001), and osteoarthritis (p = 0.022). Moreover, OST associated with a power Doppler US score (rho 0.442; p = 0.001) and a greyscale US score (rho 0.591; p < 0.001). In both groups males had significantly higher OST values than females and OST associated moderately weakly with body mass index (rho patients 0.316, rho controls 0.24; all, p < 0.001).

Conclusion: Patients with RA showed higher OST values in comparison to controls. Moreover, OST associated with clinical, US, and laboratory disease activity markers.