Background/Purpose:

Metacarpophalangeal joint (MCPj) swelling in Psoriatic Arthritis (PsA) can be produced both by synovitis (IAS) and peritenon extensor tendon inflammation (PTI), having been  this last lesion reported by some authors as an enthesitis-like lesion. Our objective was to explore the association of PTI and IAS with enthesitis in PsA, using the enthesis US score MASEI (Madrid Sonographic Enthesis Index).

Methods:

27 consecutive non selected PsA patients were included. An expert rheumatologist obtained US images from the dorsal aspect of 2nd to 5th MCPj of both hands evaluating IAS and PTI in grey scale (GS) and power Doppler (PD), and also performed the MASEI examination. In addition to the PD item of MASEI (defined as signal in bone profile or intratendon or bursa at the enthesis), PD OMERACT was evaluated as present or absent (defined as signal in the enthesis ²2 mm to the bone profile). We used a MyLab 70 XVG machine, Esaote, Genoa, Italy, with a GS 13 MHz probe and 7.1 MHz PD frequency, PRF 750 Hz and 60 Gain. 3-5 seconds videos of each MCPj and enthesis were obtained in transverse and longitudinal views for further reliability analysis. Reliability of IAS and PTI was performed by 5 readers (true US result was the consensus of at least three) and MASEI«s by 3 readers (true US result was the consensus of at least two). For qualitative reliability analysis, mean Cohen kappa was used for PD, IAS and PTI, and intraclass correlation coefficient (ICC) for MASEI based on a mean-rating of three readers, absolute-agreement, two-way mixed effect model. Statistical association between IAS, PTI and MASEI was analyzed with T student test. SPSS statistical package version 20 (SPSS Inc, Chicago, IL) was used.

Results:

Eighteen patients had PTI PD (66,7%) and same value for SIA PD. The inter-reader reliability for PTI and IAS was good with kappa values of 0.685 and 0.680 respectively. The inter-reader reliability for MASEI was excellent with ICC 0,922 (CI 95% 0,846-0,960). The inter-reader reliability for PD MASEI was ICC 0,921(CI 95% 0,855-0,963) and for PD OMERACT ICC 0.895 (CI 95% 0,802-0,949). Table 1 shows the existence of association between PTI and enthesitis identified by PD. This association was not found with IAS. PTI, both GS and PD, showed a significant relation with IAS PD (p 0.009 and p 0.037, respectively). IAS GS didn«t show any relation with PTI both PD (p 0.055) and GS (p 0.334).

Table 1. Relation between IAS and PTI with MASEI and different PD subtypes. Results are expressed as mean ± standard deviation (SD).

Conclusion:

The present study finds PTI to be associated with enthesitis as opposed to MCPj synovitis, which may support a functional association between PTI and enthesis, and reinforces the role of PTI in PsA as an enthesis-like lesion.