Vinod Chandran, MBBS, MD, DM, PhD
The relationship between enthesitis and synovitis is of considerable interest to both clinicians and researchers. This relationship is best evaluated using imaging, particularly ultrasonography, and could provide pathophysiologic insights. Balulu and colleagues recruited 158 patients with PsA who underwent sonographic assessment of 52 joints, 40 tendons, and 14 entheses as well as clinical evaluation. Overall, total sonographic enthesitis scores were significantly associated with total sonographic synovitis and sonographic tenosynovitis scores and also with older age, male sex, swollen joint count, C-reactive protein, physical occupation, and patient-reported outcomes. The association between enthesitis and synovitis was also demonstrated at the elbows, knees, and ankles. This study demonstrates that psoriatic enthesitis and synovitis are closely related and thus may share pathophysiologic mechanisms. Longitudinal studies in very early PsA using ultrasound might provide clues to confirm the hypothesis that psoriatic synovitis is secondary to enthesitis.
Another important domain that is increasingly studied is axial PsA. Currently, the evidence for treatment of axial PsA is extrapolated from that for axial spondyloarthritis (SpA), in the belief that the two diseases are pathophysiologically similar. However, there is increasing evidence for differences between axial PsA and axial SpA that might influence the choice of treatment. In a recent study, de Hooge and colleagues demonstrated that patients with axial PsA have lower severity of damage to the spine compared with those with axial SpA. Using data from 312 patients with PsA and 213 patients with SpA who underwent radiographic imaging assessment in the Belgian Epidemiological Psoriatic Arthritis Study (BEPAS) and the Ghent and Belgian Inflammatory Arthritis and Spondylitis (Be-GIANT) study, respectively, they show that the proportion of patients with PsA vs SpA having spinal damage was comparable. Patients with SpA and spinal damage had higher modified Stoke Ankylosing Spondylitis Spine Scores, indicating more severe damage. These results are consistent with other published studies and indicate that patients with PsA have less severe spinal disease compared with other patients with axial SpA. Randomized controlled trials (RCTs) specifically investigating the treatment of axial PsA are currently underway. Nevertheless, post hoc analyses of data from PsA RCTs indicate that most drugs efficacious for PsA overall also provide benefit in axial disease.
In a recent report, Baraliakos and colleagues analyzed data from the SELECT-PsA 1 and SELECT-PsA 2 trials that evaluated the efficacy of upadacitinib in PsA. They show that, compared with placebo, 15 mg upadacitinib led to a greater improvement in axial symptoms. The improvement in overall Bath Ankylosing Spondylitis Disease Activity Index score at week 24 was significantly higher with 15 mg upadacitinib compared with placebo in both trials. However, these results are not definitive because there is yet no consensus on the definition of and outcome measures for axial PsA.