title: Peripheral joint inflammation in early onset spondyloarthritis is not specifically related to enthesitis.
abstract: OBJECTIVE
  A pivotal MRI study of knee arthritis indicated that enthesitis was more frequently observed in established spondyloartritis (SpA) than rheumatoid arthritis (RA). Subsequent MRI and ultrasound studies, however, failed to consistently demonstrate primary synovitis in RA versus primary enthesitis in SpA. Therefore, the current study aimed to reassess enthesitis versus synovitis in peripheral arthritis by a combined imaging and histopathological study in early untreated disease.
  
  
  METHODS
  MRI and mini-arthroscopic synovial biopsy sampling were performed in 41 patients with early untreated knee or ankle arthritis, who were diagnosed with SpA (n=13), RA (n=20) or crystal arthropathy (n=8) at follow-up. MRI evaluation of enthesitis and synovitis, and immunohistochemical characterisation of synovitis were performed by two observers blinded to diagnosis.
  
  
  RESULTS
  MRI showed similar prevalence of perientheseal fluid/oedema (67% vs 75%), perientheseal bone marrow oedema (0% vs 10%) and entheseal enhancement (46% vs 47%) in SpA versus RA, respectively. The number and distribution of affected entheseal sites were not different between both diseases. The MRI synovitis score was significantly higher in SpA (median 1.4; IQR 1.1-1.5) compared with RA (median 0.5; IQR 0.0-1.3) (p=0.028). Synovial histopathology showed a numerical increase in infiltrating cells in SpA versus RA synovitis which reached significance for CD163 macrophages in the synovial sublining (p=0.030). There were no differences compared with the crystal arthropathy control group.
  
  
  CONCLUSIONS
  Enthesitis on MRI is not a specific feature of peripheral arthritis in recent onset SpA versus RA. Synovitis is prominent in both diseases as evaluated by MRI and immunohistochemistry.
authors.affiliation: Department of Clinical Immunology and Rheumatology, Academic Medical Center/University of Amsterdam, , Amsterdam, The Netherlands.
authors.forename: Jacqueline E
authors.initials: JE
authors.lastname: Paramarta
authors.forename: Christiaan
authors.initials: C
authors.lastname: van der Leij
authors.forename: Ioana
authors.initials: I
authors.lastname: Gofita
authors.forename: Nataliya
authors.initials: N
authors.lastname: Yeremenko
authors.forename: Marleen G
authors.initials: MG
authors.lastname: van de Sande
authors.forename: Maria J
authors.initials: MJ
authors.lastname: de Hair
authors.forename: Paul P
authors.initials: PP
authors.lastname: Tak
authors.forename: Mario
authors.initials: M
authors.lastname: Maas
authors.forename: Dominique
authors.initials: D
authors.lastname: Baeten
mesh_terms: D000328:Adult; D017668:Age of Onset; D000843:Ankle Joint / Q000473:pathology; D001172:Arthritis, Rheumatoid / Q000150:complications; D001182:Arthroscopy; D001706:Biopsy; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000473:pathology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D012720:Severity of Illness Index; D025241:Spondylarthritis / Q000150:complications*; D013583:Synovial Membrane / Q000473:pathology; D013585:Synovitis / Q000175:diagnosis / Q000209:etiology* / Q000473:pathology; D052256:Tendinopathy / Q000175:diagnosis / Q000209:etiology* / Q000473:pathology
keywords: Inflammation; Magnetic Resonance Imaging; Rheumatoid Arthritis; Spondyloarthritis; Synovitis