Objectives To establish the consistency of the previously reported pattern of muscle involvement in a large cohort of patients with molecularly defined ryanodine receptor type 1 (RYR1)–related myopathies, to identify possible additional patterns, and to compare magnetic resonance imaging (MRI) findings with clinical and genetic findings.
Design Blinded analysis of muscle MRI patterns of patients with congenital myopathies with dominant or recessive RYR1 mutations and control patients without RYR1 mutations. We compared MRI findings with the previously reported pattern of muscle involvement.
Setting Data from 3 tertiary referral centers.
Patients Thirty-seven patients with dominant or recessive RYR1 mutations and 23 controls with other myopathies.
Main Outcome Measures Each MRI was classified as typical if it was identical to the reported pattern, consistent if it was similar to the reported one but with some additional features, or different. Images with no or few changes were classified as uninformative.
Results Twenty-one of 37 patients with RYR1 mutations had a typical pattern; 13 had a consistent pattern. Two patients had uninformative MRIs and only 1 had a different pattern. Compared with patients with dominant mutations, patients with recessive mutations and ophthalmoparesis had a more diffuse pattern, classified as consistent in 6 of 8. In contrast, 10 of 11 with recessive mutations but without ophthalmoparesis had a typical pattern. All MRIs of 23 control patients were classified as different.
Conclusions Our results suggest that muscle MRI is a powerful predictor of RYR1 involvement in patients with a congenital myopathy, especially if they carry a dominant mutation or recessive mutations without ophthalmoparesis.