Early and Mid-Term Ultrasound Response to Guselkumab in Psoriatic Arthritis: A Real-World Cohort from a Single Tertiary Rheumatology Center

<b>Objective:</b> To quantify early and mid-term changes in ultrasound-detected synovitis and enthesitis after initiating guselkumab in psoriatic arthritis (PsA) and to contextualize imaging responses alongside clinical outcomes. <b>Methods:</b> We conducted a retrospective single-center cohort study of consecutive CASPAR-classified adults (<i>n</i> = 20) initiating guselkumab 100 mg (week 0/week 4, then q8w; q4w intensification per routine practice). Power Doppler ultrasound (PDUS) followed EULAR-OMERACT standards at baseline (T0), Month 3 (T3), and Month 6 (T6). The primary endpoint was within-patient change in 24-joint GLOESS. Secondary endpoints included OMERACT entheseal scores (activity-only; activity + structure), DAPSA states, PASI, and 6-month persistence. Within-patient changes were assessed using Wilcoxon signed-rank tests (two-sided). <b>Results:</b> All 20 patients completed T6. GLOESS decreased from T0 to T3 (mean Δ -4.05 ± 2.78; <i>p</i> = 0.0312) and to T6 (mean Δ -5.70 ± 4.05; <i>p</i> = 0.0001). Component summaries showed a numerically larger early decrease in synovial PD signal than in grayscale synovial hypertrophy (descriptive). Enthesitis scores improved: OMERACT activity-only median Δ -2.0 at T3 (<i>p</i> = 0.0313) and -3.5 at T6 (<i>p</i> = 0.016); activity + structure median Δ -1.5 at T3 (<i>p</i> = 0.0412) and -3.0 at T6 (<i>p</i> = 0.031). The estimated structural component (OMERACT-1 minus OMERACT-2) was similar across visits (descriptive), indicating improvements driven predominantly by inflammatory signal suppression rather than detectable changes in structural lesions over 6 months. Among patients with baseline PD-positive enthesitis (<i>n</i> = 7), PD negativity (OMERACT-2 = 0) occurred in 2/7 (28.6%) by T6. Clinical domains (DAPSA, PASI) improved in parallel, and 6-month persistence was high. <b>Conclusions:</b> In routine care, guselkumab was associated with a significant improvement in PD-inclusive ultrasound synovitis scores by 3 months, which deepened by 6 months, alongside an improvement in entheseal activity measures. Over 6 months, entheseal structural burden appeared stable; these findings should be considered hypothesis-generating and warrant confirmation in prospective controlled studies.