Evaluation of Baseline Sonographic Enthesitis as a Predictor of Clinical Enthesitis Response to TNF-α and IL-17 Inhibitors Among Patients with Psoriatic Arthritis

Objectives Enthesitis is a hallmark feature of psoriatic arthritis (PsA), contributing to pain, disability, and radiographic damage. Detection of clinical enthesitis (CE), defined as tenderness on palpation of entheseal sites, is influenced by non-inflammatory pain and examiner variability. Sonographic enthesitis (SE) provides a more objective assessment of inflammatory and structural lesions at the enthesis but has seldom been used as an outcome in clinical trials.[1] This study aimed to assess whether baseline SE is associated with clinical response after 3 months of TNF-α or IL-17 inhibitor therapy and whether this association differs across biologic classes Methods In a single-center cohort of PsA patients fulfilling CASPAR criteria, those initiating systemic therapy for active musculoskeletal disease were invited to an ultrasound sub-study. A retrospective analysis of stored ultrasound scans included participants treated with TNF-α or IL-17 inhibitors. CE was assessed at baseline and 3 months using the SPARCC Enthesitis Index. SE was evaluated at 16 bilateral sites for grayscale and power Doppler abnormalities following a standardized protocol,[2] including quadriceps, distal patella, tibial tuberosity, Achilles, plantar fascia, triceps, lateral epicondyle, and supraspinatus insertions. Elementary lesions (hypoechogenicity, thickening, erosion, enthesophyte, calcification, Doppler signal) were scored individually using a semi-quantitative score, then combined into composite scores representing total lesion burden, inflammation, and structural damage. An active SE count was calculated based on sites with a Doppler signal plus hypoechogenicity or thickening. A multivariable logistic regression model was used to assess associations between baseline SE scores and resolution of CE at follow-up, adjusting for age, sex, baseline SPARCC score, prior advanced therapy, and biologic therapy class. Results Seventy-eight patients were included in the analysis, with 42 on TNF-α inhibitors and 36 on IL-17 inhibitors. At baseline, mean SPARCC score was 1.8 (SD 1.8), with 68% showing at least 1 CE site. Mean active SE count was 1.4 (SD 1.7), with 65% showing at least 1 SE site. After 3 months of treatment, mean SPARCC decreased to 1.1 (SD 1.6; p=0.01), and 42% still had at least 1 CE site. None of the SE composite scores, nor biologic class (OR 1.31, 95% CI 0.48-3.58; p=0.603), were significantly associated with CE resolution (Table 1). Table 1: Association between baseline sonographic enthesitis and resolution of clinical enthesitis at follow-up visit (N=78) Conclusion Baseline composite SE scores were not associated with CE responses to treatment, likely reflecting the limited correlation between SE and CE at baseline. Further studies are needed to evaluate associations at individual entheses and determine whether serial sonographic assessments can better capture treatment response. References [1.] Eder L. J Rheumatol 2023;50:258-64. [2.] Eder L. J Rheumatol 2020;96:50-2.