0551: Enthesitis Beyond the Surface: Ultrasonographic Unmasking of Preclinical Psoriatic Arthritis in Cutaneous Psoriasis

Background/Purpose: Psoriatic arthritis (PsA) develops insidiously from psoriasis (PsO), with enthesitis representing a critical initial site of inflammation. Musculoskeletal ultrasonography (MSUS) enables the identification of subclinical entheseal abnormalities and offers potential for stratifying PsA evolution into preclinical phases, long before clinical arthritis is apparent. This study aimed to determine whether inflammatory ultrasonographic changes are present in the absence of clinically overt enthesitis among patients with early PsA and PsO.

Methods: A cross-sectional observational study enrolled 153 subjects. The PsA group included 87 patients (58.6% female, mean age 44.3±8.2 years), diagnosed per CASPAR criteria within 3 years of onset. The PsO-only group comprised 66 patients (62.1% female, mean age 42.1±10.3 years) without musculoskeletal symptoms. Mean age at psoriasis onset was 27.4±6.1 years in the PsA group and 25.9±7.3 years in the PsO group. Mean age of arthritis onset in PsA was 41.2±7.8 years. All participants underwent clinical and MSUS evaluation of peripheral entheses (Achilles tendon, plantar fascia, patellar ligament, quadriceps tendon, lateral epicondyle), with scoring of entheseal thickness, hypoechogenicity, erosions, enthesophytes, and Power Doppler (PD) signal. Early PsA patients were subclassified as: preclinical (n=12); subclinical (n=31) and prodromal (n=44).

Results: In the PsA group, 71/87 (81.6%) had active enthesitis on MSUS, including 58.3% with PD signal. Among them, Achilles enthesitis (64.6%) and plantar fascia (48.9%) were most affected. In the PsO group, 29/66 (43.9%) had subclinical enthesitis, and 11 (16.7%) demonstrated PD positivity (Table 1).

Table 1. Ultrasonographic Enthesitis Features Across PsA and PsO Patients

Group/Subgroup	N (patients)	MSUS enthesitis (%)	PD (+) (%)	Enthesophytes (%)	Bone erosions (%)	Mean entheseal thickness (mm)
PsA – total	87	81.6	58.3	34.2	17.6	4.6±0.9
Preclinical	12	58.3	8.3	25.0	8,3	3.5±0.9
Subclinical	31	70.9	22.6%	32,3	12,9	3.9±0.9
Prodromal	44	95.4	97.7	45,5	31,8	4.3±0.9
PsO - total	66	43.9	16.7	19.6	3.0	3.2±0.6

Enthesophytes were detected in 34.2% of PsA and 19.6% of PsO (p=0.031). Bone erosions were present in 17.6% of PsA vs. 3.0% in PsO (p< 0.001). A significantly higher mean entheseal thickness (4.6 ± 0.9 mm vs. 3.2 ± 0.6 mm, p< 0.001) and frequency of bilateral involvement were found in PsA.

Conclusion: MSUS enables precise phenotyping of early PsA, detecting entheseal inflammation in both symptomatic and asymptomatic PsO patients. The stratification of patients across preclinical, subclinical, and prodromal phases supports enthesitis as an early marker of transition to PsA. Routine ultrasound surveillance in PsO may facilitate timely diagnosis and therapeutic interception of PsA progression.