title: Thigh muscle MRI in immune-mediated necrotising myopathy: extensive oedema, early muscle damage and role of anti-SRP autoantibodies as a marker of severity.
abstract: OBJECTIVE
  The aims of this study were to define the pattern of muscle involvement in patients with immune-mediated necrotising myopathy (IMNM) relative to those with other inflammatory myopathies and to compare patients with IMNM with different autoantibodies.
  
  
  METHODS
  All Johns Hopkins Myositis Longitudinal Cohort subjects with a thigh MRI (tMRI) who fulfilled criteria for IMNM, dermatomyositis (DM), polymyositis (PM), inclusion body myositis (IBM) or clinically amyopathic DM (CADM) were included in the study. Muscles were assessed for intramuscular and fascial oedema, atrophy and fatty replacement. Disease subgroups were compared using univariate and multivariate analyses. Patients with IMNM with anti-signal recognition particle (SRP) autoantibodies were compared with those with IMNM with anti-HMG-CoA reductase (HMGCR) autoantibodies.
  
  
  RESULTS
  The study included 666 subjects (101 IMNM, 176 PM, 219 DM, 17 CADM and 153 IBM). Compared with DM or PM, IMNM was characterised by a higher proportion of thigh muscles with oedema, atrophy and fatty replacement (p<0.01). Patients with IMNM with anti-SRP had more atrophy (19%, p=0.003) and fatty replacement (18%, p=0.04) than those with anti-HMGCR. In IMNM, muscle abnormalities were especially common in the lateral rotator and gluteal groups. Fascial involvement was most widespread in DM. Fatty replacement of muscle tissue began early during the course of disease in IMNM and the other groups. An optimal combination of tMRI features had only a 55% positive predictive value for diagnosing IMNM.
  
  
  CONCLUSIONS
  Compared with patients with DM or PM, IMNM is characterised by more widespread muscle involvement. Anti-SRP-positive patients have more severe muscle involvement than anti-HMGCR-positive patients.
authors.affiliation: National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Iago
authors.initials: I
authors.lastname: Pinal-Fernandez
authors.affiliation: Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Maria
authors.initials: M
authors.lastname: Casal-Dominguez
authors.affiliation: Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: John A
authors.identifier: http://orcid.org/0000-0003-3472-2469
authors.initials: JA
authors.lastname: Carrino
authors.affiliation: Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Arash H
authors.initials: AH
authors.lastname: Lahouti
authors.affiliation: Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Pari
authors.initials: P
authors.lastname: Basharat
authors.affiliation: Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Jemima
authors.initials: J
authors.lastname: Albayda
authors.affiliation: Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Julie J
authors.initials: JJ
authors.lastname: Paik
authors.affiliation: Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Shivani
authors.initials: S
authors.lastname: Ahlawat
authors.affiliation: Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Sonye K
authors.initials: SK
authors.lastname: Danoff
authors.affiliation: Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Lloyd
authors.affiliation: National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, Maryland, USA.|Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Mammen
authors.affiliation: Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Lisa
authors.initials: L
authors.lastname: Christopher-Stine
mesh_terms: D050154:Adiposity; D000328:Adult; D000368:Aged; D000906:Antibodies / Q000097:blood*; D001284:Atrophy / Q000000981:diagnostic imaging; D015415:Biomarkers / Q000097:blood; D003882:Dermatomyositis / Q000000981:diagnostic imaging; D004487:Edema / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D006903:Hydroxymethylglutaryl CoA Reductases / Q000276:immunology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging / Q000473:pathology*; D009135:Muscular Diseases / Q000097:blood / Q000000981:diagnostic imaging* / Q000276:immunology; D018979:Myositis, Inclusion Body / Q000000981:diagnostic imaging; D009336:Necrosis / Q000097:blood / Q000000981:diagnostic imaging / Q000276:immunology; D017285:Polymyositis / Q000000981:diagnostic imaging; D011237:Predictive Value of Tests; D012720:Severity of Illness Index; D018271:Signal Recognition Particle / Q000276:immunology*; D013848:Thigh
chemical_list: D000906:Antibodies; D015415:Biomarkers; D018271:Signal Recognition Particle; C553220:HMGCR protein, human; D006903:Hydroxymethylglutaryl CoA Reductases
keywords: Autoantibodies; Dermatomyositis; Magnetic Resonance Imaging; Polymyositis