Background Clinical metacarpophalangeal joint (MCPj) swelling is a frequent finding in psoriatic arthritis (PsA). It is assumed to be caused by intra-articular synovitis (IAS). However, ultrasound (US) have also demonstrated in PsA peritenon inflammation of the extensor digitorum tendon (PTI).To date the data about the significance of this two lesions (IAS and PTI) in MCPj swelling are sparse.
Objectives Our objective was to explore PTI and IAS as the cause of clinical MCPj swelling in PsA patients.
Methods 27 consecutive non selected PsA patients, fulfilling CASPAR criteria, with clinical involvement of at least one 2nd to 5th MCPj were included. A MyLab 70 XVG machine, Esaote, Genova, Italy, with a greyscale (GS) 13 MHz probe, and a 7.1 MHz power Doppler (PD) frequency (PRF 750 Hz, Gain 60) was used. Videos (3–5 sec) of each MCPj 2nd to 5th of both hands in transversal and longitudinal views were obtained for central reader analysis, scoring US as presence or absence in GS and PD of: 1) PTI (defined as an hypoechoic swelling of the soft tissue surrounding the extensor tendon at MCPj level with or without PD) and 2) IAS (OMERACT definition). US pathology for each joint and lesion was defined as at least three of five central readers having the same score. SPSS analysis was performed for frequencies, percentage of agreement and Cohen's Kappa test.
Results 27 PsA patients with a mean (SD) age of 56 (11) years and disease duration 109 (101) months were included. Isolated peripheral involvement was present in 21 patients (78%) and 6 (22%) had both axial and peripheral affection. Mean (SD) CRP level was 8.3 (8.2) mg/l and ESR 21.9 (19.3) mm. The mean DAS28 ESR was 3.88 (1.23). Psoriasis involvement included skin and nails in 15 (55.5%) of the patients.
A total of 216 MCPj were examined, with 60 (27,7%) being clinically swollen. The figure illustrates the agreement between clinical and US assessments, and the table shows the kappa values for the agreements. PTI in at least one MCPj was found in 19/27 patients (70%) with a total of 41/216 locations (19%) in GS. For IAS, there was GS in at least one MCPj in 23/27 patients (85%) with a total of 63/216 locations (29%). 28 of 41 (68.3%) joints had both PTI and IAS.
Conclusions Our study identifies two different US lesions (IAS and PTI) causing clinical joint swelling. PTI is near as frequent as IAS as a cause of MCPj swelling, and future studies are necessary to explore the added value of assessing PTI for prognosis or treatment.
Disclosure of Interest None declared