Letter to the Editor

We read with interest the article by Boeters DM et al. [1]. We would like to clarify the significant findings and suggest further research needed to validate the novel conclusion. In ACPA-negative patients, 1 sustained DMARD-free remission (SDFR) occurred over 5 years follow-up in 17 (6%) with baseline low (< 30) MBDA score vs approximately 50% remissions in both moderate (30–44) and high (> 44) MBDA score patients ([1], Fig. 1). All ACPA-positive RA patients had low percentages of SDFR and no difference was found by baseline MBDA score category [1]. Percentages of 3 MBDA categories did not differ (p = 0.470) between the ACPA-positive and ACPA-negative groups [1].

SDFR was recently reported by ACPA-negative vs ACPA-positive patients in the total Leiden early arthritis cohort (1993–2016; n = 1296) [2], from which the Boeters et al. study [1] was the most recent inclusion subgroup (2011–2016). In the total inclusion period (1993–2011), SDFR occurred between 5 and 15% in ACPA-positive RA vs 40 to 50% in the ACPA-negative RA [2], as in Boeters et al. [1].

Unexpectedly, in multivariate analyses ([1], Table 2), the 95 ACPA-negative RA patients with high (> 44) baseline scores had greater DMARD-free remission than the 17 reference patients with low (< 30) MBDA scores (p = 0.041). If MBDA were truly a marker of disease activity, one might expect low rather than high MBDA to predict SDFR. Alternatively, if ACPA-negative RA does consist of subgroups [1], its documentation will require further serological study in separate cohorts [2, 3] or search for genetic markers [3]. Confounding variables should be excluded, possibly clinical features related to age at onset, which was found to be a significant (p = 0.036) predictor of SDFR ([1], Table 2) and other disease variables not studied. Is it conceivable that this anomaly [1] is due to chance occurrence in a small sample size study leading to an incorrect conclusion, especially when borderline (p = 0.041) statistical correlation is found [1]?

A critical review of the value of multibiomarker disease activity score to predict remission in RA was recently published [4]. The challenging question is whether or not baseline MBDA (or serological markers) are being overinterpreted or overstated with respect to outcomes (or disease subgroups) was critically analyzed [4].