title: Combining MRI and muscle biopsy improves diagnostic accuracy in subacute-onset idiopathic inflammatory myopathy.
abstract: BACKGROUND
  In 10-20% of patients with subacute-onset idiopathic inflammatory myopathy (IIM), muscle biopsy is normal or shows nonspecific findings. MRI can be used as a triage test before muscle biopsy and as an add-on test if the biopsy is nondiagnostic.
  
  
  METHODS
  MRI scans of skeletal muscles and muscle biopsies were evaluated prospectively in 48 patients suspected to have IIM. The interpretations of MRI and muscle biopsy were compared with the definite diagnosis (based on European Neuromuscular Centre criteria and response to corticosteroids).
  
  
  RESULTS
  The false negative rate (FNR) of all muscle biopsies was 0.23. Biopsies of a muscle showing hyperintensity on MRI (as triage test) had an FNR of 0.19. The result of MRI as an add-on test in patients with a nondiagnostic muscle biopsy decreased the FNR from 0.23 to 0.06.
  
  
  CONCLUSIONS
  We recommend both MRI and muscle biopsy in patients suspected of having IIM.
authors.affiliation: Department of Neurology, Academic Medical Center, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: Janneke
authors.initials: J
authors.lastname: Van De Vlekkert
authors.forename: Mario
authors.initials: M
authors.lastname: Maas
authors.forename: Jessica E
authors.initials: JE
authors.lastname: Hoogendijk
authors.forename: Marianne
authors.initials: M
authors.lastname: De Visser
authors.forename: Ivo N
authors.initials: IN
authors.lastname: Van Schaik
mesh_terms: D000328:Adult; D001706:Biopsy / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000473:pathology*; D009220:Myositis / Q000175:diagnosis* / Q000453:epidemiology / Q000503:physiopathology; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013848:Thigh / Q000502:physiology; D034941:Upper Extremity / Q000473:pathology
keywords: dermatomyositis; idiopathic inflammatory myopathy; muscle MRI; muscle biopsy; myositis