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

Abstract

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.

Keywords: arthritis; psoriatic; ultrasonography.

Figure 1

Characteristic ultrasound pathologies in early dactylitic patients with PsA. (A) Longitudinal view through the fifth metatarsophalangeal joint illustrating synovitis within a dactylitic toe. There is grey scale synovitis (grade 3) with effusion (*) and abnormal power Doppler signal (grade 2, right image) consistent with ‘active’ synovitis. (B) Periarticular cortical bone irregularity at the second MCP joint confirmed in the longitudinal (left) and transverse planes, respectively (right), confirming erosion. A common site of erosion in PsA and in dactylitis. (C) Longitudinal view at the MCP joint displaying power Doppler signal above the extensor tendon (PTI). (D) Image in the transverse plane showing the fifth metatarsal head, the most frequent site of erosion in feet, demonstrating periarticular bone irregularity (arrow). Bone irregularity was confirmed further in the longitudinal plane to signify erosion. There is also surrounding grey scale synovial hypertrophy (grade 2). (E) Transverse view of volar aspect of dactylitic third toe showing diffuse soft tissue oedema (large arrow) and flexor tenosynovitis (small arrow). MCP, metacarpophalangeal; MC, metacarpal head; MT, metatarsal head; P, phalanx; PsA, psoriatic arthritis; PTI, peritendon inflammation.