Muscle Magnetic Resonance Imaging for the Differentiation of Multiple AcyI-CoA Dehydrogenase Deficiency and Immune-mediated Necrotizing Myopathy

Background： Clinically, it is difficult to differentiate multiple acyl-CoA dehydrogenase deficiency （MADD） from immune-mediated necrotizing myopathy （IMNM） because they display similar symptoms. This study aimed to determine whether muscle magnetic resonance imaging （MRI） could be used for differential diagnosis between MADD and IMNM. Methods： The study evaluated 25 MADD patients, confirmed by muscle biopsy and ETFDH gene testing, and 30 IMNM patients, confirmed by muscle biopsy. Muscles were assessed for edema and fatty replacement using thigh MRI （tMRI）. Degrees and distribution patterns of fatty infiltration and edema in gluteus maximus and thigh muscles were compared. Results： Total fatty infiltration and edema scores （median, [Q 1, Q3]） were 4.00 （1.00, 15.00） and 0 （0, 4.00） in MADD and 14.50 （8.00, 20.75） and 22.00 （16.75, 32.00） in IMNM, respectively, which were significantly more severe in IMNM than that in MADD （P = 0.000 and P = 0.004~ respectively）. Edema scores tbr gluteus maximus, long head of biceps femoris, and semimembranosus were significantly higher in IMNM than in MADD （all P = 0.000）. Fatty infiltration scores for anterior and medial compartments were significantly more severe in IMNM than that in MADD （all P = 0.000）. Conclusion： Different patterns of muscle involvement on tMRI can contribute to differential diagnosis between MADD and IMNM when clinical suspicions alone are insufficient, thereby reducing the need for muscle biopsy.

“Target” and “Sandwich” Signs in Thigh Muscles have High Diagnostic Values for Collagen VI-related Myopathies

Background： Collagen Vl-related myopathies are autosomal dominant and recessive hereditary myopathies, mainly including Ullrich congenital muscular dystrophy （UCMD） and Bethlem myopathy （BM）. Muscle magnetic resonance imaging （MRI） has been widely used to diagnosis muscular disorders. The purpose of this study was to evaluate the diagnostic value of thigh muscles MRI for collagen VI-related myopathies. Methods： Eleven patients with collagen VI gene mutation-related myopathies were enrolled in this study. MRI of the thigh muscles was performed in all patients with collagen VI gene mutation-related myopathies and in 361 patients with other neuromuscular disorders （disease controls）. Tl-weighted images were used to assess fatty infiltration of the muscles using a modified Mercuri＇s scale. We assessed the sensitivity and specificity of the MRI features of collagen Vl-related myopathies. The relationship between fatty infiltration of muscles and specific collagen VI gene mutations was also investigated. Results： Eleven patients with collagen VI gene mutation-related rnyopathies included six UCMD patients and five BM patients. There was no significant difference between UCMD and BM patients in the fatty infiltration of each thigh muscle except sartorius （P = 0.033）： theretbre, we combined the UCMD and BM data. Mean fatty infiltration scores were 3.1 and 3.0 in adductor magnus and gluteus maximus, while the scores were 1.3, 1.3, and 1.5 in gracilis, adductor longus, and sartorius, respectively. A “target” sign in rectus femoris （RF） was present in seven cases, and a “sandwich” sign in vastus lateralis （VL） was present in ten cases. The “target” and “sandwich” signs had sensitivities of 63.6% and 90.9% and specificities of 97.3% and 96,9% for the diagnosis of collagen Vl-related myopathies, respectively. Fatty infiltration scores were 2.0-3.0 in seven patients with mutations in the triple-helical domain, and 1.0-1.5 in three of four patients with mutations in the N- or C-domain of the collagen VI genes. Conclusions： The “target” sign in RF and “sandwich” sign in VL are common MRI features and are useful for the diagnosis of collagen VI-related myopathies. The severity of fatty infiltration of muscles may have a relationship with the mutation location of collagen VI gene.