Dactylitis – A Clinical Marker for a More Severe Phenotype in DMARD-Naive Early PsA

In patients with disease-modifying antirheumatic drug (DMARD)-naive early psoriatic arthritis (PsA), dactylitis denotes a more severe disease phenotype independently associated with an increased disease burden, with greater swollen joint count (SJC), C-reactive protein (CRP) levels, ultrasound-detected synovitis, and bone erosions, according to study results published in the Annals of the Rheumatic Diseases.

Researchers enrolled patients with early PsA who met the classification criteria for PsA (CASPAR). Participants’ clinical examination included tender joint count (TJC) and SJC. The early PsA cohort was divided by the presence of or the absence of dactylitis at baseline (PsA with dactylitis, or the dactylitic PsA group) or PsA without dactylitis (nondactylitic PsA group).

A total of 177 DMARD-naive patients with early PsA were included in the current analysis from the Leeds Spondyloarthropathy Register for Research and Observation in the United Kingdom.

Dactylitic PsA occurred in 46% (n=81) of the participants; nondactylitic PsA occurred in 54% (n=96) of the participants. The mean participant age was 43.7 years in the dactylitic PsA group and 44.4 years in the nondactylitic PsA group.

Significantly more individuals in the dactylitic PsA group than in the nondactylitic PsA group had a symptom duration of less than 24 months (84% vs 66.7%, respectively; P =.008).

Median TCJs and SJCs were significantly greater in patients with dactylitic PsA than in those with nondactylitic PsA (TJCs, 9 vs 4, respectively; P <.01 and SJCs, 7 vs 1, respectively; P <.001). Polyarthritis was the dominant phenotype among those with dactylitic PsA (65.4%; P <.01) and oligoarthritis in those with nondactylitic PsA (86.5%; P <.001).

Further, dactylitis was more common in the toes (68.2%) than in the fingers (31.8%). Overall, “hot” dactylitis was more prevalent than “cold” dactylitis (83.6% vs 16.4%, respectively).

In addition, ultrasound-derived synovitis and erosions were significantly more common in patients with dactylitic PsA than in those with nondactylitic PsA (P <.001 for both). With exclusion of digits affected by dactylitis, ultrasound synovitis remained significantly more common in patients with dactylitic PsA than in those with nondactylitic PsA (P <.001). Synovitis (ie, grey scale of ≥2 and/or power Doppler of ≥1) was reported in 53.7% of those with dactylitis.

As a limitation, researchers noted the inability to show clinically meaningful differences in ultrasound enthesopathy associated with the outcomes used in the study, despite differences observed for clinical enthesitis.   

Researchers concluded, “[Dactylitis] may be an important discriminator for risk stratification in early intervention strategies.”

Reference

Dubash S, Alabas OA, Michelena X, et al. 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. Ann Rheum Dis. Published online December 10, 2021. doi:10.1136/annrheumdis-2021-220964