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Original Contributions |

Muscle Magnetic Resonance Imaging in Congenital Myopathies Due to Ryanodine Receptor Type 1 Gene Mutations

Andrea Klein, MD; Heinz Jungbluth, PhD; Emma Clement, MD, ChB; Suzanne Lillis, MSc, BSc; Stephen Abbs, PhD; Pinki Munot, MD; Marika Pane, MD, PhD; Elizabeth Wraige, MD; Ulrike Schara, MD; Volker Straub, MD, PhD; Eugenio Mercuri, PhD; Francesco Muntoni, MD
Arch Neurol. 2011;68(9):1171-1179. doi:10.1001/archneurol.2011.188.
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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.

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Figure 1. Schematic diagram of the typical pattern in RYR1-related myopathies. A, In the thighs, the rectus femoris (RF), adductor longus (AL), and gracilis (G) are spared and in some patients hypertrophied; the adductor magnus (AM), sartorius (S), vastus lateralis (VL), vastus intermedius (VIM), and vastus medialis (VM) are affected; the hamstrings are less affected; and the involvement of semimembranosus (SM) and semitendinosus (ST) is nonspecific. BF indicates biceps femoris. B, In the calf, the most affected muscle is the soleus (SO), followed by the gastrocnemius lateralis (GL) and to a lesser effect the gastrocnemius medialis (GM). In the anterior compartment, which is less affected than the posterior, the peroneal group (PG) is more affected than the tibialis anterior (TA). EDL indicates extensor digitorum longus; FDL, flexor digitorum longus; and TP, tibialis posterior.

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Figure 2. Typical pattern in magnetic resonance imaging of the thigh (images in the left column) and the calf (images on the right). A and B, Patient 12 is 8 years of age, with moderately severe disease. C and D, Patient 6 has a moderate phenotype. E and F, Patient 16 is 13 years of age with a severe phenotype; relatively spared rectus femoris, adductor magnus, gracilis, and to a lesser extent the sartorius; and with the soleus most affected in the calf.

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Figure 3. Magnetic resonance imaging findings in patients with recessive mutations. A, B, and C, Axial T1-weighted images with a typical pattern in patient 26, 14 years of age, with recessive disease without ophthalmoplegia. More diffuse but still recognizable relative sparing of the rectus, adductor longus, and gracilis muscles is seen. D, E, and F, Patient 19 with a mild phenotype without ophthalmoparesis in a proximal view, middle thigh, and calf, respectively. G, Axial images of the thigh of patient 32, 18 years of age, with ophthalmoplegia reveal diffuse, atrophic muscles, relative sparing of the rectus, and hypertrophied adductor longus affected on the central part. H and I, Axial images of the calf and proximal thigh, respectively, of patient 33, 10 years of age, with ophthalmoplegia. In this patient, compatible but diffuse involvement of vasti, rectus, and adductor longus only marginally less involved than the adductor magnus are seen.

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