Background Preliminary results demonstrate that the peritenon inflammation of the extensor digitorum tendon (PTI) is a specific ultrasound (US) pattern of Psoriatic Arthritis (PsA) at metacarpophalangeal joint (MCPj) level. It was suggested as a pattern playing a key role in the differential diagnosis between Rheumatoid Arthritis and PsA (1,2).
Objectives In spite of PTI's clinical impact, there are no data regarding the reliability of US PTI evaluation. The present study addressed this topic by testing the reliability of US on evaluation of PTI.
Methods 27 consecutive non selected PsA patients with clinical involvement of at least one 2nd to 5th MCPj were included. A rheumatologist trained in PTI assessments obtained the US images exploring the dorsal aspect of MCPj from 2nd to 5th of both hands using 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 and a 60 Gain. 3–5 seconds videos of each MCPj were obtained in transversal and longitudinal views for further reliability analysis. In the inter-reader reliability analysis, performed by five readers from five different hospitals and four countries, it was scored as present or absent 1) PTI (defined as an hypoechoic swelling of the soft tissue surrounding the extensor tendon at MCPj level with or without PD) and 2) intra-articular synovitis (IAS, OMERACT definition), both in PD and GS. The consensus of true US results for every joint and lesion was achieved when at least three readers had the same opinion. Cohen's Kappa test was used for statistical analysis.
Results Clinical MCPj involvement was present in 60 (27.7%) of the 216 joints whereas US detected IAS and/or PTI in 75 (34.7%). US showed GS PTI in 41 (19%) and PD in 38 (17.6%) of the joints, while GS IAS was found in 63 (29.2%) with PD activity in 41 (19%) of the joints. The inter-reader reliability is shown in the Table. Intra-reader reliability results expressed as mean Kappa were 0.826 for PTI PD, 0.784 for PTI GS, 0.743 for IAS PD and 0.637 for IAS GS.
Conclusions US examination of MCPj shows that PTI is near as frequent as IAS in PsA with reliability of its scoring at least as good as for joint synovitis. This opens the possibility of introducing US scoring of PTI, which may be of importance for the diagnosis and follow-up of PsA patients.
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Zabotti A et al. Clinical and Experimental Rheumatology 2016; 34: 459–465.
Disclosure of Interest None declared