P101 Investigating the association between clinical enthesitis and central sensitisation in psoriatic arthritis
Authors: Aldehmi Norah M , Basu Neil , Dale James , Najm Aurelie , Sunzini Flavia 
Published: April 2024

Abstract

Background/Aims
Psoriatic Arthritis (PsA) is an inflammatory arthritis with enthesitis as its characteristic clinical feature. Enthesitis can be clinically challenging to differentiate from the widespread pain associated with Fibromyalgia (FM), the prototype of central sensitisation (CS) present in up to 30% of PsA patients. Algometry is used in CS research to quantify pressure pain threshold (PPT), reflecting increased pain sensitivity when reduced. Ultrasound is a valuable tool to evidence entheseal inflammatory changes in PsA. This study investigates associations between CS, i.e., FM, and entheseal ultrasound outcomes to better characterise pain mechanisms in PsA enthesitis.

Methods
A total of 20 patients with active PsA about to start a new immunosuppressant were recruited. Ultrasound evaluation of non-dominant knee (left for all patients) using dynamic B-mode and power Doppler was performed alongside the Leeds Enthesitis Index (LEI) collection to assess enthesitis. PPT was measured with algometry at the non-dominant knee (enthesitis), trapezius and calf muscle (CS areas), and collection of the ACR 2011 FM criteria was used to determine the presence of CS. Non-dominant areas were selected because they are less likely to exhibit biomechanical ultrasound alterations; moreover, the non-dominant side is generally more sensitive than the dominant side, thus enabling more precise PPT measurements. Correlations and t-tests were used to test associations between variables collected. SPSS was used to analyse the data.

Results
The 30% of patients met the FM criteria and presented higher LEI scores and lower PPT evoked threshold than FM-negative patients. Total FM scores significantly correlated with LEI scores (r = 0.69, p &lt; 0.001) and calf PPTs (r=-0.53, p=-0.014), but not with knee and trapezius PPTs (r=-0.49, p = 0.09; r=-0.30, p = 0.19), or US enthesitis (r=-0.04, p = 0.86). PPTs in the areas investigated did not show significant correlations with US enthesitis, while an indirect association was observed between LEI with calf PPT (r=-0.51, p = 0.02) and trapezius PPT (r=-0.41, p = 0.06). No significant correlation was demonstrated between LEI and left knee enthesitis (r=-0.32, p = 0.17).

Conclusion
FM is frequent in PsA and can mimic entheseal pain, as suggested by the strong correlation with the LEI scores. In our cohort, LEI scores did not efficiently capture inflammatory enthesitis, demonstrated by the lack of association with ultrasound data. Moreover, the association between objective measurement of CS, including calf and trapezius PPTs, supports that LEI score may primarily reflect the presence of central sensitisation rather than inflammation. Therefore, relying solely on clinical detection of enthesitis may result in inappropriate treatment escalation. Ultrasound, conversely, serves as a dependable tool for confirming enthesitis and providing valuable information for making informed treatment decisions.

Disclosure
N.M. Aldehmi: None. N. Basu: None. J. Dale: None. A. Najm: None. F. Sunzini: None.