Maxime Verhoeven

216 Chapter 12 LETTER To the Editor: A recent paper of Triantafyllias et al. described that optical spectral transmission (OST-) scores, obtained by the HandScan, were significantly higher in male compared to female rheumatoid arthritis (RA) patients and controls, and an association between OST-score and age, BMI, and hand surface area was found. 1 The difference in gender that Triantafyllias et al. showed is in line with results of studies performed at our department. We developed and validated a new disease activity index, DAS-OST, in which tender and swollen joint counts are replaced by the OST-score. In the construction of the DAS-OST formula, gender had to be taken into account, because also in this study, OST-scores were higher in males than in females. 2 In addition, by comparing single OST-scores to the rheumatologist’s clinical classification into active or inactive RA as reference, also different optimal cut-offs for males and females were calculated, again indicating a gender difference. Based on these findings we investigated whether this difference in gender is also observed in controls (30 males vs. 45 females). This indeed turned out to be the case, p=0.02, in line with the results of Triantafyllias et al. The Figure shows OST-scores in RA patients and controls, separately for males and females, indicating the gender difference, and the difference between RA- patients (generally low disease activity) and controls, although there are considerable overlaps in scores between the four subgroups. We further aimed to quantify the OST-score differences between males and females in RA patients as well as in controls, and to determine which factors influence OST- scores, including gender. In total 77 participants were included in this study. In this whole sample, adjusting for cohort (RA vs. controls), no statistically significant difference in gender was found (p=0.12). However, in the subgroup of controls (i.e., 22 females vs. 15 males) a statistically significant difference in OST-score was observed (p=0.05), in contrast to in the subgroup of RA patients (p=0.90, 20 females vs. 20 males). A possible explanation of the latter result, and of the absence of a statistically significant gender difference when analyzing the whole sample could be a difference in disease activity between male and female RA patients. Unfortunately, we were not able to adjust, for this, as disease activity data were not available. For OST-scores in the male subgroup, predictors were cohort, i.e., RA patients vs. controls (estimate, i.e., mean difference in OST-score, -3.08, 95%CI -6.52 to 0.36, indicating lower OST-scores in controls), age (estimate -0.15, 95%CI -0.29 to -0.02, indicating lower OST-scores in older persons), and hand surface area (estimate 0.24, 95%CI 0.03 to 0.45, indicating higher OST-scores with larger hand surface area). For OST-scores in the female subgroup, these were cohort (estimate -4.33, 95%CI -7.17 to -1.49, indicating lower OST-scores in controls), BMI (estimate -0.44, 95%CI -0.79 to -0.09, indicating lower OST-scores with higher BMI)