Fig. 2
From: MRI patterns of thigh muscle involvement in immune-mediated necrotizing myopathy and dermatomyositis
Representative thigh MRIs of immune-mediated necrotizing myopathy (IMNM) and dermatomyositis (DM). (A, B) Muscle edema of selective posterior compartment muscles (semimembranosus [arrow] and biceps femoris-long head [BF-LH] [arrowhead], sparing the semitendinosus [open arrow] and biceps femoris-short head [BF-SH] [open arrowhead]) on short tau inversion recovery (STIR) images in IMNM cases with shorter disease duration. (C, D) On T1-weighted (T1W) images, complete fatty replacement of the semimembranosus (arrow) and BF-LH (arrowhead) with persistent sparing of the BF-SH (open arrowhead) in IMNM cases with prolonged disease duration. The semitendinosus is relatively spared (open arrow, C) or has undergone significant fatty replacement (black arrow, D). (E-H) Muscle and fascial edema of anterior compartment muscles, semitendinosus (arrow), and BF-SH (arrowhead) on T2-weighted fat-saturated (T2FS) images in DM