title: Comparative analyses of muscle MRI and muscular function in anti-synthetase syndrome patients and matched controls: a cross-sectional study.
abstract: Magnetic resonance imaging (MRI) of thigh muscles is increasingly used to assess disease activity and damage extent in chronic myositis, but the validity of the findings is not clear. Here, the primary aim was to compare thigh MRI findings in patients having chronic myositis associated with anti-synthetase syndrome (ASS) and in matched healthy controls.
  
  
  
  Cross-sectional analyses of thigh muscle MRI, muscular function and creatinine kinase (CK) were performed in 68 ASS patients (median disease duration 71 months) and 67 controls matched for age and gender. MRI changes associated with disease activity (edema in muscles and fascia) and damage (fatty replacement and muscle volume reduction) were assessed semiquantitatively, giving a total MRI score of 0-78 (total edema 0-42 and total damage 0-36).
  
  
  
  ASS patients had higher total MRI score than the matched controls (14.1 versus 3.0; p < 0.001) and less muscle strength (p < 0.001). Muscle edema was more frequent in ASS patients than controls (38% versus 12%), as was fatty replacement (42% versus 4%). In ASS patients, we found that the total edema score correlated with CK, but 23% of the patients with normal CK had score > 18. Muscle compartment analyses in ASS patients showed that muscle edema was most pronounced anteriorly, while fatty replacement dominated posteriorly.
  
  
  
  This study showed, for the first time, the magnitude of difference in muscle MRI findings between chronic myositis cases and matched controls. In ASS patients, muscle MRI appeared to provide useful complementary information to muscle strength and CK levels in the assessment of myositis.
authors.affiliation: Institute of Clinical Medicine, Department of Rheumatology, Oslo University Hospital, Pb 4950 Nydalen, 0424, Oslo, Norway. helena.andersson@medisin.uio.no.
authors.forename: Helena
authors.identifier: 0000-0003-4114-293X
authors.initials: H
authors.lastname: Andersson
authors.affiliation: Department of Radiology, Oslo University Hospital, Oslo, Norway.
authors.forename: Eva
authors.initials: E
authors.lastname: Kirkhus
authors.affiliation: Department of Rheumatology, Oslo University Hospital, Oslo, Norway.
authors.forename: Torhild
authors.initials: T
authors.lastname: Garen
authors.affiliation: Department of Orthopedic Surgery, Oslo University Hospital, Oslo, Norway.
authors.forename: Ragnhild
authors.initials: R
authors.lastname: Walle-Hansen
authors.affiliation: Department of Radiology, Oslo University Hospital, Oslo, Norway.
authors.forename: Else
authors.initials: E
authors.lastname: Merckoll
authors.affiliation: Institute of Clinical Medicine, Department of Rheumatology, Oslo University Hospital, Pb 4950 Nydalen, 0424, Oslo, Norway.
authors.forename: Øyvind
authors.initials: Ø
authors.lastname: Molberg
mesh_terms: D000328:Adult; D003402:Creatine Kinase / Q000097:blood / Q000378:metabolism; D003404:Creatinine / Q000097:blood / Q000378:metabolism; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging* / Q000201:enzymology / Q000503:physiopathology; D009220:Myositis / Q000000981:diagnostic imaging* / Q000201:enzymology / Q000503:physiopathology
chemical_list: D003404:Creatinine; D003402:Creatine Kinase
keywords: Anti-synthetase antibody; Anti-synthetase syndrome; Muscle function; Muscle magnetic resonance imaging; Myositis