Using ultrasound to define inflammatory and non-inflammatory phenotypes in difficult-to-treat psoriatic arthritis

Abstract

Objective: To investigate the prevalence of difficult-to-treat psoriatic arthritis (D2T-PsA) and classify patients with persistent inflammatory PsA (PIPsA) and non-inflammatory PsA (NIPsA) based on a combination of clinical and musculoskeletal ultrasound (MSUS) evidence of inflammation.

Methods: A multicentre cross-sectional study was conducted on PsA patients treated with biological disease-modifying anti-rheumatic drugs/targeted synthetic disease-modifying anti-rheumatic drugs (b/tsDMARDs). D2T-PsA status was characterised by an inadequate response to ≥2 classes of b/tsDMARDs and the persistence of active disease, defined as a DAPSA >14.

Results: Out of 517 PsA patients on b/tsDMARDs, 53 (10.3%) met the criteria for D2T-PsA with 30 (57%) classified as PIPsA and 23 (43%) classified as NIPsA. The PIPsA phenotype had higher swollen joint count (2.5 (IQR 1.0-7.0) vs 0.0 (IQR 0.0-1.0), p<0.001), dactylitis (20% vs 0%, p=0.030) and nail psoriasis (40% vs 13%, p=0.027). Conversely, NIPsA patients had significantly greater ΔPtGA-PhGA (4.0 (IQR 2.5-5.0) vs 0.0 (IQR 0.0-1.5), p<0.001), higher tender points (16.0 (IQR 0.0-18.0) vs 0.0 (IQR 0.0-8.0), p=0.009), a higher SPARCC enthesitis index (5.0 (IQR 2.0-8.0) vs 2.0 (IQR 0.0-5.0), p=0.023). The MSUS showed higher ultrasound activity (3.81±2.0 vs 0.91±0.5, p<0.001) and greater structural damage (4.12±1.0 vs 2.38±2.1, p<0.001), with both activity and damage scores being higher in PIPsA patients.

Conclusion: The classification into PIPsA and NIPsA based on easily detectable clinical features can support a tailored therapeutic management of patients with D2T-PsA.

Keywords: Arthritis, Psoriatic; Inflammation; Pain; Ultrasonography.

Figure 1. Flow diagram of patients enrolled in the study. b/tsDMARDs, biologic/target synthetic disease-modifying anti-rheumatic drugs; D2T, difficult-to-treat; LDA, low disease activity; PsA, psoriatic arthritis.

Figure 2. Prevalence of PIPsA and NIPsA in D2T-PsA. D2T, difficult-to-treat; PIPsA, persistent inflammatory psoriatic arthritis; NIPsA, non-inflammatory psoriatic arthritis.

Figure 3. Comparison of DAPSA scores and components between PIPsA and NIPsA patients. CRP, c-reactive protein; DAPSA, disease activity index for psoriatic arthritis; NIPsA, non-inflammatory psoriatic arthritis; PIPsA, persistent inflammatory psoriatic arthritis; PtGA, patient global assessment; SJC, swollen joint count; TJC, tender joint count; VAS pain, Visual Analogue Scale pain.

Figure 4. The comparison of clinical characteristics between PIPsA and NIPsA phenotypes in D2T-PsA reveals key differences. PIPsA phenotype is primarily characterised by joint swelling, dactylitis and nail psoriasis, along with higher PhGA levels. In contrast, the NIPsA phenotype is defined by tender, non-swollen joints, a higher number of tender points, a fibromyalgia diagnosis based on the ACR 2016 criteria, elevated SPARCC enthesitis index and a greater discrepancy between PtGA and PhGA. D2T, difficult-to-treat; NIPsA, non-inflammatory psoriatic arthritis; PhGA, physician global assessment; PIPsA, persistent inflammatory psoriatic arthritis; PsA, psoriatic arthritis; PtGA, patient global assessment.

Figure 5. Sonographic characteristics of PIPsA and NIPsA. (A) Comparison of Activity and Damage scores between PIPsA and NIPsA. (B) Mean number of sonographic findings, including synovitis, paratenonitis, tenosynovitis and enthesitis, in PIPsA vs NIPsA patients. NIPsA, non-inflammatory psoriatic arthritis; PIPsA, persistent inflammatory psoriatic arthritis.