Background: Musculoskeletal joint ultrasound (US) is becoming increasingly utilized in patients with both early and established spondyloarthritis (SpA) for diagnostic, disease activity assessment, and prognostic purposes. However, there is no consensus on the number and sites of joints to be examined by US for the evaluation of both inflammatory and structural lesions in SpA patients. Therefore, a precise and feasible US scoring system for synovitis is needed.

Objectives: Development of a new US synovitis score (SONAR-7) with evaluation of its diagnostic performance and validity in a cohort of patients with Psoriatic Arthritis (PsA) and axial Spondyloarthritis (axSpA) in comparison to healthy controls (HC).

Methods: We recruited 121 participants: 41 patients with PsA, 39 with axSpA from six Swiss hospital outpatient clinics, and 41 healthy controls (HC). All completed questionnaires on quality of life and physical activity and underwent a clinical examination of joints, which included 68-tender joint count (TJC) and 66-swollen joint count (SJC), as well as assessment of 29 entheses. A detailed musculoskeletal US examination was also performed: 22 joints were examined, based on the PsA-Son 22 score [1], to assess for grayscale (GS) and power Doppler (PD) synovitis, scored semi-quantitatively (0-3) according to the Outcome Measures in Rheumatology criteria [2]. Erosions and new bone formation (NBF) were recorded as present or absent (0/1). Additionally, 18 entheses and multiple tendons (wrist, hand, and ankle flexors/extensors) were examined by US and scored (0/1) for B-mode and PD.

To identify the optimal combination of joint regions that best discriminated between SpA patients and HC, we utilized univariable and multivariable logistic regression to analyze the association between the synovitis in different joints and a diagnosis of SpA. We also assessed the best subset of sites using the Least Absolute Shrinkage and Selection Operator (LASSO) method, with L1 regularization to select out less predictive variables.

Results: After performing univariable analyses, we excluded 4/11 joints (2nd/3rd proximal interphalangeal (PIP) joints of the hand, 5th metacarpophalangeal (MCP) joint, and 3rd PIP of the foot) because they were not associated with a diagnosis of SpA. The newly developed score, “SONAR-7”, evaluates GS synovial thickening and PD synovitis across seven joints: 2nd and 3rd MCP joints, 2nd and 3rd distal interphalangeal (DIP) joints of the hands, 1st metatarsophalangeal (MTP) joints, knees, and wrists. All 7 joints showed either a significant association or a strong trend toward significance in distinguishing between SpA and HC in the regression analysis (Table 1). The SONAR-7 score achieved an area under the receiver operating characteristic curve (AUC) of 0.831 (95% CI 0.76–0.91), with excellent specificity (95.1%) and moderate sensitivity (44%), comparable to other US scores (Figure 1). The inflammatory score (combined GS and PD) of the SONAR-7 correlated significantly with clinical measures of inflammation and disease activity scores, with coefficients of 0.37 for SJC, 0.35 for clinical enthesitis, -0.30 for the Short Form-12 health survey (SF-12), 0.33 for Disease Activity in Psoriatic Arthritis (DAPSA) score, 0.24 for the 28-joint Disease Activity Score, 0.48 for B-mode enthesitis, and 0.44 for PD enthesitis. NBF correlated significantly with the Health Assessment Questionnaire (p=0.035) and the Bath Ankylosing Spondylitis Metrology Index (p=0.016).

Conclusions: The SONAR-7 score is a fast and effective ultrasound-based tool for evaluating synovitis in patients with PsA and axSpA. It demonstrated high specificity and good sensitivity for detecting inflammatory activity, good convergent construct validity, and reliable performance across examiners. The focused assessment of a limited number of key joints would enhance the feasibility and the integration of an US score such as this into daily rheumatologic practice.

REFERENCES: [1] Ficjan A, Husic R, Gretler J, et al. Ultrasound composite scores for the assessment of inflammatory and structural pathologies in Psoriatic Arthritis (PsASon-Score). Arthritis Res Ther . 2014;16(5):476.

[2] D’Agostino MA, Terslev L, Aegerter P, et al. Scoring ultrasound synovitis in rheumatoid arthritis: a EULAR-OMERACT ultrasound taskforce—Part 1: definition and development of a standardised, consensus-based scoring system. RMD Open . 2017;3(1):e000428.

Acknowledgments: NIL.

Disclosure of Interests: Gehad G. Elsehrawy: None declared, Delphine S Courvoisier: None declared, Erik Deman: None declared, Diana Dan: None declared, Raphael Micheroli RM received consultancy fees from AbbVie, UCB, J&J, and Eli Lilly, Hans Ziswiler: None declared, Pascal Zufferey: None declared, Laure Brulhart Bletsas: None declared, Michael J. Nissen Honoraria for lectures from AbbVie, Janssen, Eli Lilly, Novartis, Pfizer, and UCB., Consulting for AbbVie, Janssen, Eli Lilly, Novartis, Pfizer, and UCB.