title: Do dermatomyositis and polymyositis affect similar thigh muscles? A comparative MRI-based study.
abstract: OBJECTIVE
  Dermatomyositis (DM) and polymyositis (PM) commonly cause weakness of the thigh muscles. However, it is debated whether DM and PM affect similar thigh muscles. Muscle oedema on fat-suppressed MRI sequences is thought to represent active inflammation. In this study, we aimed to assess which thigh muscle groups are preferentially inflamed in DM and PM, respectively, using short-tau inversion-recovery MRI sequences.
  
  
  METHODS
  We analysed 71 patients from 2 Rheumatology centres, 31 with DM and 40 with PM diagnosed according to the Bohan and Peter criteria. MRI oedema (1=present, 0=absent) was assessed bilaterally on fat-suppressed sequences in 17 pelvic floor and thigh muscles. An MRI oedema score (range 0-17) was calculated by adding the separate scores bilaterally and dividing them by two. Inter-rater variability was assessed by intraclass correlation coefficient. Fisher's exact test was used to compare binomial data.
  
  
  RESULTS
  Age and gender ratio were similar in patients with DM and PM. Disease duration (months, mean±SD) was shorter (20±31) in DM than in PM (53±69) (p=0.02). The intraclass correlation coefficient between the radiologists involved was 0.78. Muscle oedema was more common in DM than in PM except in the posterior thigh muscles. In particular, 68% of patients with DM had involvement of at least one anterior thigh muscle versus 38% of patients with PM (p=0.02).
  
  
  CONCLUSIONS
  Compared with PM, DM affects more thigh muscles, except those of the posterior compartment, which are equally involved in both disorders. These findings may be useful to target physiotherapy at the more frequently affected muscles.
authors.affiliation: Department of Rheumatology, Department of Internal Medicine, Azienda Ospedaliera ASMN, IRCSS, Reggio Emilia, Italy. pipitone.nicolo@asmn.re.it.
authors.forename: Nicolo
authors.initials: N
authors.lastname: Pipitone
authors.affiliation: Department of Rheumatology, University of Bari, Italy.
authors.forename: Antonella
authors.initials: A
authors.lastname: Notarnicola
authors.affiliation: Department of Radiology, Department of Internal Medicine, Azienda Ospedaliera ASMN, IRCSS, Reggio Emilia, Italy.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Levrini
authors.affiliation: Department of Radiology, Department of Internal Medicine, Azienda Ospedaliera ASMN, IRCSS, Reggio Emilia, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Spaggiari
authors.affiliation: Department of Radiology, University of Bari, Italy.
authors.forename: Arnaldo
authors.initials: A
authors.lastname: Scardapane
authors.affiliation: Department of Rheumatology, University of Bari, Italy.
authors.forename: Florenzo
authors.initials: F
authors.lastname: Iannone
authors.affiliation: Department of Rheumatology, University of Bari, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Lapadula
authors.affiliation: Department of Radiology, Department of Internal Medicine, Azienda Ospedaliera ASMN, IRCSS, Reggio Emilia, Italy.
authors.forename: Pierpaolo
authors.initials: P
authors.lastname: Pattacini
authors.affiliation: Department of Rheumatology, Children's Hospital of Pittsburgh, USA.
authors.forename: Giulio
authors.initials: G
authors.lastname: Zuccoli
authors.affiliation: Department of Rheumatology, Department of Internal Medicine, Azienda Ospedaliera ASMN, IRCSS, Reggio Emilia, Italy.
authors.forename: Carlo
authors.initials: C
authors.lastname: Salvarani
mesh_terms: D000328:Adult; D000368:Aged; D003882:Dermatomyositis / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging*; D017285:Polymyositis / Q000000981:diagnostic imaging*; D013848:Thigh / Q000000981:diagnostic imaging*