[Use of muscular MRI in inflammatory myopathies]

Inflammatory myopathies include polymyositis (PM), dermatomyositis (DM) and inclusion body myositis (IBM) which differ in terms of clinical, immuno-histological presentations, evolution and treatment. Diagnosis is based on the muscular biopsy but histological distinction between PM and IBM can be difficult; biopsies can be insufficient as well as during follow-up to detect active areas within the muscle.

Muscular MRI is an important tool both in the diagnosis and the follow-up of IMM in the following circumstances: Distinction between PM and IBM: fatty infiltration and involvement of the anterior group of the thighs are characteristic of IBM whereas isolated inflammation and involvement of the three thighs or posterior muscle groups are characteristic of PM. Biopsy guidance on the inflammatory lesions depicted on the STIR sequence either initially or after a non-conclusive biopsy. To differentiate, active disease from steroid myopathy.

Several multicentric trials are in development both in spectro and morphologic MRI to study hypoxic phenomenon in early course of IMM and muscular volume evaluation both in normal subjects, congenital or acquired myopathies.