The application of MRI in sporadic inclusion-body myositis

Objective: To investigate the characteristic MRI features of sporadic inclusion-body myositis (sIBM). Methods: Clinical and MR imaging data of 6 patients with sIBM diagnosed by muscle biopsy from May 2013 to November 2014 were retrospectively analyzed. All patients showed insidious onset of lower limb muscle weakness and diagnosed as sIBM by muscle biopsies. All patients were evaluated by the score of the severity of fatty infiltration, inflammation and atrophy in MRI. Results: All patients were observed fatty infiltration with different degrees. The fatty infiltration in thighs was characterized in a decreasing order of frequency: gluteus maximus (6 cases), vastuslateralis (6 cases), vastusintermedius (6 cases), vastusmedialis (6 cases), sartorius (5 cases), adductor magnus (5 cases), rectus femoris (4 cases), semi-membranosus (4 cases), semi-tendinosus (4 cases), biceps femoris (4 cases), gracilis (3 cases), adductor longus (2 cases). The fatty infiltration in thighs was characterized in a decreasing order of severity: vastuslateralis (3.2 points), vastusintermedius (3.2 points), vastusmedialis (3.0 points), adductor magnus (3.0 points), gluteus maximus (2.7 points), bicepsfemoris (2.2 points), semi-membranosus (2.1 points), semi-tendinosus (2.1 points), rectus femoris (1.5 points), sartorius (1.3 points), gracilis (0.8 points), adductor longus (0.7 points). All patients showed the features of distal distribution andsymmetry. Inflammation was observed in 3 patients. 1 patient only involved the vastuslateralis, the other 2 patients were observed muscle inflammation with different degrees in 12 muscles. Atrophy was observed in 5 patients. The atrophy in thighs was characterized in a decreasing order of frequency: vastuslateralis (5 cases), vastusintermedius (5 cases), vastusmedialis (4 cases), adductor magnus (4 cases), semi-membranosus (2 cases), rectus femoris (1 cases), sartorius (1 cases) and gluteus maximus; there was no atrophy in adductor longus, gracilis, semi-tendinosus, biceps femoris. Conclusion: The MRI characteristic manifestations of sIBM is fatty infiltration and atrophy in the distal portion, particularly involving the vastuslateralis, vastusintermedius, vastusmedialis and adductor magnus. (authors)