The synergistic efficacy of hydroxychloroquine with methotrexate is accompanied by increased erythrocyte mean corpuscular volume

Abstract

Objectives: To determine whether concomitant HCQ modulates the increase in erythrocyte mean corpuscular volume (MCV) caused by MTX therapy, and whether this is associated with improved clinical response in RA.

Methods: A retrospective observational analysis was conducted on two independent hospital datasets of biologic-naïve, early-RA patients who started oral MTX. Baseline characteristics, DAS28-ESR and monthly MCV after starting MTX were obtained. Conventional and machine-learning statistical approaches were applied to the discovery cohort (Cohort 1, 655 patients) and results validated using Cohort 2 (225 patients).

Results: HCQ therapy with MTX was associated with a 2-fold increase in the likelihood of response defined in this study as clinical remission or low disease activity at 6 months (P <0.001). The improved clinical outcome of combination HCQ and MTX therapy was associated with an accelerated rise in MCV from 2 months after commencing therapy. The increase in MCV at 3 months was equivalent to the contemporaneous reduction in the DAS (DAS28-ESR) in predicting clinical response at 6 months. Using latent class mixed modelling, five trajectories of MCV change over 6 months from baseline were identified. The odds ratio of response to treatment was 16.2 (95% CI 5.7, 46.4, P <0.001) in those receiving combination therapy classified within the MCV elevation >5 fl class, which contained the most patients, compared with MTX alone.

Conclusion: Our data provide mechanistic insight into the synergistic clinical benefit of concomitant HCQ with MTX, boosting the rise in MCV, which could serve as a companion biomarker of treatment response.

Keywords: HCQ; MTX; biomarker; mean corpuscular change; synergistic.

Fig. 1

HCQ boosts the MCV elevation caused by MTX, which is associated with improved clinical outcome (Cohort 1) (A) Multiple logistic regression using variables selected by least absolute shrinkage and selection operator regression to predict MTX response (defined as remission or low disease activity, DAS28-ESR < 3.2) at 6 months. (B) Changes in MCV after initiation of MTX with or without HCQ stratified by responder (R) vs non-responder (NR) status. Linear mixed model was used to estimate mean changes of MCV at each time point from baseline. Mean changes (shown in the boxes) with 95% CI are shown in the plot. A heatmap demonstrating P-values of pairwise comparisons of MCV increase (at monthly intervals) between the treatment and response groups is also shown. MCV: mean corpuscular volume; OR: odds ratio.

Fig. 2

Trajectories of latent class of MCV change over 6 months after initiation of MTX (Cohort 1) The five classes are: (i) Fall MCV: reduction in MCV; (ii) MCV <5: MCV increase <5 fl; (iii) No change: no MCV change; (iv) MCV >5: MCV increase >5 fl; and (v) Bi-phasic: initial reduction in MCV followed by an increase, from baseline. The number of patients in each class (A) and their MCV trajectories (B) are shown. (C) Stratification of the trajectories of the five-class model between non-responders and responders. (D) Mosaic plot illustrating cross-sectional distribution of patients from each latent class stratified by treatment response and treatment. MCV: mean corpuscular volume.