Synovitis and radiographic progression in non-erosive and erosive hand osteoarthritis: is erosive hand osteoarthritis a separate inflammatory phenotype?

OBJECTIVE: To compare the prevalence of synovitis, pain and radiographic progression in non-erosive and erosive hand osteoarthritis (HOA), and to explore whether the different rate of disease progression is explained by different levels of synovitis and structural damage. DESIGN: We included 31 and 34 participants with non-erosive and erosive HOA at baseline, respectively. Using Generalized Estimating Equations, we explored whether participants with erosive HOA had more synovitis (by MRI, ultrasound and clinical examination) independent of the degree of structural damage. Similarly, we explored whether pain at baseline and radiographic progression after 5 years were higher in erosive HOA, independent of the levels of synovitis and structural damage. All analyses were adjusted for age and sex. RESULTS: Power Doppler activity was found mainly in erosive HOA. Participants with erosive HOA demonstrated more moderate-to-severe synovitis, assessed by MRI (OR = 1.73, 95% CI 1.11-2.70), grey-scale ultrasound (OR = 2.02, 95% CI 1.25-3.26) and clinical examination (OR = 1.80, 95% CI 1.44-2.25). The associations became non-significant when adjusting for more structural damage. The higher frequency of joint tenderness in erosive HOA was at least partly explained more structural damage and inflammation. Radiographic progression (OR = 2.53, 95% CI 1.73-3.69) was more common in erosive HOA independent of radiographic HOA severity and synovitis (here: adjusted for grey-scale synovitis by ultrasound). CONCLUSION: Erosive HOA is characterized by higher frequency and more severe synovitis, pain and radiographic progression compared to non-erosive HOA. The higher rate of disease progression was independent of baseline synovitis and structural damage.