Optical spectral transmission higher in RA patients, tied to disease activity markers

Optical spectral transmission (OST) values are higher among patients with rheumatoid arthritis than controls, results of a study have shown. OST is also associated with clinical, ultrasound, and laboratory disease activity markers.

The researchers measured OST in the metacarpophalangeal, proximal intraphalangeal, and wrist joints of 168 patients with RA and 114 controls. OST difference between the two groups was statistically examined and subsequently controlled for the effect of possible confounding factors. Receiver-operating characteristics were used to test the diagnostic OST performance.

Additionally, Spearman correlation coefficient and a generalized linear statistical model were used to assess the associations of OST with clinical and serological activity markers (patient group), joint ultrasound (patient subgroup), and various anthropometric and epidemiologic parameters (patient and control groups).

The RA group had significantly higher OST than the control group even after adjustment for confounding factors (area under the curve [AUC], 1.89, 95 percent confidence interval [CI], 0.709–3.070; p=0.002). With ultrasound as reference, AUC for all 1,251 joints was 0.67 (95 percent CI, 0.631–0.709).

Correlation and adjustment analyses in the patient group revealed the associations of OST with various disease activity markers (28-joint count Disease Activity Score [rho, 0.313; p=0.001], swollen joint counts [rho, 0.361; p=0.001], C-reactive protein [rho, 0.389; p=0.001], age [rho, 0.276; p<0.001], and osteoarthritis [p=0.022]). OST also correlated with power Doppler ultrasound score (rho, 0.442; p=0.001) and greyscale ultrasound score (rho, 0.591; p<0.001).

Moreover, OST was significantly higher among males than females and correlated moderately weakly with body mass index (rho patients, 0.316; rho controls, 0.24; p<0.001 for all) in both groups.