Relationship between monocytes to lymphocytes ratio and axial spondyloarthritis

Axial spondyloarthritis (axSpA) is a progressive, chronic, inflammatory skeletal disorder affecting the spine and sacroiliac joints. Many studies have shown that neutrophils, lymphocytes, monocytes, platelets, and red blood cells (RBCs) play important roles in the inflammatory process of axSpA. Neutrophils to lymphocytes ratio (NLR) and red blood cell distribution width (RDW) have been reported to be simple and inexpensive markers to indicate the disease activity of axSpA. However, the role of monocytes to lymphocytes ratio (MLR) and platelets to lymphocytes ratio (PLR) in axSpA was rarely mentioned.

The study's aim was to determine the role of MLR and PLR in axSpA patients and to investigate their relationships with disease severity.

AxSpA patients who fulfilled the Assessment in Ankylosing Spondylitis International Society classification criteria published in 2009 were enrolled in this study and divided into nonradiographic axial spondyloarthritis (nr-axSpA) group and ankylosing spondylitis (AS) group. Healthy age and gender-matched subjects were also enrolled as control group. MLR, PLR, NLR, RDW, C-reactive protein (CRP) level, and erythrocyte sedimentation rate (ESR) level were assessed. The correlation between the variables with finger-to-floor distance, Modified Schober test, and occiput-to-wall distance were tested with Pearson correlation. Furthermore, area under curve (AUC) value, sensitivity, specificity, and the optimal cutoff values were determined using receiver operating characteristic (ROC) curves.

A total of 148 axSpA patients (67 nr-axSpA patients and 81 AS patients) and 58 healthy subjects were included in the study. The MLR, NLR, PLR, and RDW in axSpA group were higher than those in the control group (P < 0.05). Among them, MLR and RDW were highly increased in AS group compared with the nr-axSpA group (P < 0.05). MLR, NLR, PLR, and RDW were all positively correlated with ESR level and CRP level (P < 0.05). MLR and RDW were positively correlated with finger-to-floor distance and negatively correlated with Modified Schober test (P < 0.05). RDW was positively correlated with occiput-to-wall distance (P < 0.05). ROC curve results showed MLR yielded a higher AUC than NLR, PLR, and RDW (P < 0.05). In addition, the optimal cutoff value of MLR for axSpA was 0.22, with a specificity of 70.9% and sensitivity of 68.4%.

MLR was elevated in AS patients compared to nr-axSpA patients and had a close relationship with CRP level, ESR level, and spine movements. MLR may be a reliable, cost-effective, and novel potential parameter to evaluate disease severity in axSpA.