Dactylitis is an indicator of a more severe phenotype independently associated with greater SJC, CRP, ultrasound synovitis and erosive damage in DMARD-naive early psoriatic arthritis

Objective: To characterise the impact of dactylitis in disease-modifying antirheumatic drug (DMARD)-naive early psoriatic arthritis (PsA).

Methods: Patients with early PsA meeting the classification criteria for PsA (CASPAR) were recruited. Clinical outcomes were recorded, and ultrasonography was conducted to assess grey scale (GS) and power Doppler (PD) synovitis, periarticular cortical bone erosions and enthesitis. The cohort was dichotomised by the presence or absence of dactylitis.

Results: Of 177 patients with PsA, those with dactylitis (dactylitic PsA (81/177, 46%)) had higher tender joint count (p<0.01), swollen joint count (SJC) (p<0.001) and C reactive protein (CRP) (p<0.01) than non-dactylitic PsA. Dactylitis was more prevalent in toes (146/214 (68.2%)) than fingers (68/214 (31.8%)); ‘hot’ dactylitis was more prevalent than ‘cold’ (83.6% vs 16.4%). Ultrasound (US) synovitis and erosions were significantly more prevalent in dactylitic PsA (p<0.001 and p<0.001, respectively). Exclusion of dactylitis in dactylitic PsA confirmed significantly greater SJC (3 vs 1, p=0.002), US synovitis (GS ≥2: 20.6% vs 16.1%, p<0.001, or PD ≥1: 5.1% vs 3.3%, p<0.001) and erosions (1.1% vs 0.5% joints, p=0.008; 26.1% vs 12.8% patients, p=0.035%) than non-dactylitic PsA. Synovitis (GS ≥2 and/or PD ≥1) occurred in 53.7% of dactylitis. No substantial differences were observed for US enthesitis.

Conclusion: Dactylitis signifies a more severe disease phenotype independently associated with an increased disease burden with greater SJC, CRP, US-detected synovitis and bone erosions in DMARD-naive early PsA and may be a useful discriminator for early risk stratification.