Do tender joints in active psoriatic arthritis reflect inflammation assessed by ultrasound and magnetic resonance imaging?

OBJECTIVE: To investigate the association between clinical joint tenderness and intra- and periarticular inflammation as assessed by ultrasound and magnetic resonance imaging (MRI) in patients with active psoriatic arthritis (PsA) and to explore if the associations differ according to patient-reported outcomes (PROs) and structural damage.

METHODS: Forty-one patients with active PsA and hand involvement had 76/78 joints examined for swelling/tenderness and ultrasound and MRI of 24 and 12 finger joints, respectively. Synovitis, tenosynovitis, periarticular inflammation and erosions were assessed using OMERACT definitions and scoring systems. Correlation between imaging inflammation sum-scores (intra-and periarticular) and tender/swollen joint counts were calculated using Spearman's rho, agreement at joint level was examined using prevalence and bias adjusted kappa (PABAK). Subgroup analyses explored the influence of PROs and radiographic erosive disease on these associations.

RESULTS: No significant correlations were found between tender or swollen joint counts and imaging inflammation sum-scores (rho=-0.31-0.38). In patients with higher level of overall pain, disability and lower self-reported mental health, a tendency towards negative correlations were found. At joint level, intra- and periarticular imaging inflammatory lesions had slight agreement with joint tenderness (PABAK=0.02-0.19) and slight to moderate with swelling (PABAK=0.16-0.54). For tender joints, agreement with imaging inflammation was even weaker in patients with either high overall pain scores, high disability scores, and/or non-erosive disease.

CONCLUSION: Joint tenderness had low association with imaging signs of inflammation in PsA patients, particularly in patients with high self-reported pain, disability and low mental health, indicating that tenderness is influenced by other parameters than local inflammation.