| To analyze the change in muscle damage under different imaging sequences using
muscle MRI in patients of necrotizing myopathy, and to analyze the distribution of muscle damage. Methods:
We recruited 16 patients with immune-mediated necrotic myopathy (IMNM) who were confirmed positive for
SRP antibodies, 14 patients with polymyositis, and 18 healthy individuals of similar age and sex with no
underlying illness. All subjects underwent thigh muscle MRI scans using T2 mapping and iterative decomposition
of water and fat with echo asymmetric and least-squares estimation (IDEAL) to quantitatively measure values in
regions of edema in muscles of both thighs. The values of T2 mapping and IDEAL were compared between the
IMNM, polymyositis, and healthy control groups and between the muscles within each group. Results: The T2
values of the IMNM and polymyositis groups were higher compared with that of the control group (P=0.021,
0.012). The IDEAL value of the IMNM group was higher than that of the control group (P=0.039); the values
showed no significant difference when compared between other groups (all P>0.05). When comparing the T2
mapping of individual muscle groups between the IMNM and control groups, statistical difference was found in
the vastus lateralis, vastus intermedius, long head of the biceps femoris, and semimembranosus; comparing the
polymyositis and control groups, statistical difference was found in the vastus lateralis, vastus intermedius, vastus
medialis, rectus femoris, and semimembranosus. When comparing the IDEAL of individual muscle groups
between the IMNM and control groups, statistical difference was found in the vastus lateralis, vastus medialis,
and semimembranosus. Conclusion: This study demonstrates the use of the non-invasive MR sequence to
quantitatively evaluate the characteristics and distribution of muscle involvement in IMNM and provides a
possible approach for the identification of other myopathy types. |