Background: Peritenon extensor tendon inflammation (PTI) patterns of Metacarpophalangeal (MCP) joints detected by ultrasound (US) are demonstrating to be enthesitis-related lesion and considered to be functional enthesitis of peripheral spondylarthritis (SpA), especially psoriatic arthritis (PsA). PTI patterns can also be observed in early rheumatoid arthritis (RA) and other connective tissue diseases (CTDs), however the frequency of PTI pattern in MCP joints in those diseases and their clinical characteristics are not clear.

Objectives: The aim of this study is to clarify the prevalence and characteristics of newly diagnosed patients with rheumatic and musculoskeletal diseases who have peritenon extensor tendon inflammation.

Methods: This was a prospective cohort study in patients with newly diagnosed rheumatic and musculoskeletal diseases with clinical swelling of at least one of the MCP joints. Demographic, clinical, and laboratory data were collected from their charts. All patients were assessed for 28 joints and the 6 entheses included in the MASEI index (bilateral triceps, quadriceps, proximal and distal patellar, Achilles tendons, and proximal insertion of plantar aponeurosis) with US examinations performed by certificated rheumatological sonographers who were blinded to clinical data. PTIs were defined as hypoechoic image surrounding the extensor digitorum tendon with or without PD signal and synovitis based on the OMERACT definition. All data analysis in this research was carried out through JMP version 17.

Results: A total of 323 patients with newly diagnosed rheumatic and musculoskeletal disease were recruited. Their final diagnosis were 245 patients with RA, 45 patients with CTDs including systemic lupus erythematosus (SLE), Sjogren syndrome, mixed connective tissue disease (MCTD), polymyositis/dermatomyositis (PM/DM) and Behcet disease, and 27 with SpA. Among them, PTIs of MCP joints were observed in 82 patients (25.4%). The mean age was 53.8 years old and 70% were female. Serum CRP levels were similar among the three groups. The positivity of PTI pattern were significantly higher in patients with SpA (n=21, 76.9%) and CTDs (n=35, 77.8%) than that in RA (n=24, 10.9%). Comparison of other findings detected with US in those patients with PTI patterns between three disease groups revealed that enthesitis were more frequent in patients with CTD and SpA than RA (RA vs CTD vs SpA; 17% vs 34% vs 57%, respectively), while the prevalence of synovitis and tenosynovitis were comparable. In the CTD group, SLE (40.0%), Sjogren (45.7%), and PM/DM (11.4%) accounted for all but one patient with CTDs with PTI patterns. In each CTD, (82.3%) with SLE, 16 (72.1%) with Sjogren syndrome, and 4 (30.8%) with PM/DM showed PTI pattens in the US.

Conclusion: We found that PTI pattern on MCP Joints is also observed frequently in patients with CTDs as well as SpA. Combination of other sites of enthesitis and serological test are useful to distinguish patients with positive PTIs among patients with RA, CTDs, and SpA.

REFERENCES: [1] Gutierrez M, Filippucci E, Salaffi F, Di Geso L, Grassi W. Differential diagnosis between rheumatoid arthritis and psoriatic arthritis: the value of ultrasound findings at metacarpophalangeal joints level. Ann Rheum Dis 2011;70:1111–4.

[2] Filippou G, Di Sabatino V, Adinolfi A, Bertoldi I, Picerno V, Biasi G, et al. No enthesis should be overlooked when psoriatic arthritis is suspected: enthesitis of the extensor digitorum tendons. J Rheumatol 2013;40:335.

Acknowledgements: NIL.

Disclosure of Interests: None declared.