Diagnostic Accuracy of Whole Body Magnetic Resonance Imaging in Inflammatory Myopathies (DARWIM)

• Evaluation of T1 and STIR (Short Tau Inversion Recovery) sequences of muscle MRI. [ Time Frame: between Day 0 and 24 months ] [ Designated as safety issue: No ]
  Description : diagnostic accuracy of muscle MRI (in terms of sensitivity, specificity, predictive positive value and predictive negative value) for the diagnostic of inflammatory myopathy.
  
  
• Presence of IIM diagnosed by muscle biopsy [ Time Frame: between Day 0 and 24 months ] [ Designated as safety issue: No ]
  Presence of IIM according to ENMC histological criteria
  
  

• Evaluation of ratio of positivity of non oriented versus oriented muscle biopsy [ Time Frame: every 3 months (up to 24 months) ] [ Designated as safety issue: No ]
  Evaluation of ratio of positivity (or sensitivity) of non oriented versus oriented muscle biopsy, using chi2 test.
  
  
• Evaluation of reproductibility intra- versus inter-observers for muscle biopsy interpretation [ Time Frame: every 3 months (up to 24 months) ] [ Designated as safety issue: No ]
  Evaluation of reproductibility intra- versus inter-observers for muscle biopsy interpretation according to ENMC (European Neuromuscular Centre) classification (calculation of Kappa coefficients).
  
  
• Evaluation of reproductibility intra- versus inter-observers for muscle MRI interpretation [ Time Frame: every 3 months (up to 24 months) ] [ Designated as safety issue: No ]
  Evaluation of reproductibility intra- versus inter-observers for muscle MRI interpretation (calculation of Kappa coefficients).
  
  

Idiopathic inflammatory myopathies (IIM) are a great concern in acquired muscle illnesses. An appropriate and rapid diagnosis is necessary, because morbidity and mortality are high and as a specific treatment is needed (corticosteroids, immunosuppressant, and "biotherapies").

Currently the use of muscle MRI in departments managing IIM is common. In absence of recommendations fixing their place in the diagnostic phase, the practices observed are extremely heterogeneous. Some systematically order a muscle MRI for patients suspected to suffer from IIM, others hold this examination for patients selected according to non defined criteria, and others sometimes use MRI to follow-up patients. This practices diversity well reflects the lack of data in the literature, making it impossible to appreciate the real contribution of this test. The results published in the great majority of studies are obtained with patients whose IIM diagnosis is already established. The diagnostic accuracy of muscle MRI in real conditions of clinical practice is thus unknown for patients having a simple suspicion of IIM.

Primary scientific aim: Evaluation of diagnostic accuracy of muscle MRI (in terms of sensitivity, specificity, predictive positive value and predictive negative value) for patients who are suspected to suffer from IIM.

Secondary scientific aim: Comparison of two diagnostic strategies: MRI-oriented muscle biopsy versus non MRI-oriented muscle biopsy.

Gold standard: muscle biopsy Index test: whole body MRI, STIR and T1 sequences Patients and setting of diagnosis tests: Screening will be realized on any patient suspected to suffer from inflammatory and addressed for muscle biopsy in one of the participating reference centres for neuro-muscular disorders.

Study calendar :

• V1 = inclusion visit Information and non-opposition of patient Collection of demographic, clinical and biological data
• V2 = muscle MRI Randomization
• V3 = muscle biopsy (oriented or non-oriented) - One year after V1, collection of the final established diagnosis