Whole‐Body Imaging Reveals Characteristic Muscle Involvement Patterns in VCP Myopathy

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Abstract
Introduction/Aims: Valosin‐containing protein (VCP) myopathy is a rare multisystem disorder with variable clinical onset and progression. While region‐focused imaging studies have provided partial information on muscle involvement, how involvement is distributed across body regions and whether this pattern is characteristic remain unclear. We aimed to characterize disease‐specific spatial patterns of muscle involvement. Methods: Twelve patients from eleven unrelated families with genetically confirmed VCP myopathy underwent CT or T1‐weighted MRI. Fat replacement in 43 muscles across shoulder, trunk, pelvis, and lower limbs was graded using the modified Mercuri score (mMS). Uniform manifold approximation and projection (UMAP) dimensionality reduction and hierarchical clustering analyses identified characteristic patterns. Clinical correlations were assessed. Results: UMAP visualization of 43 muscles showed that VCP myopathy cases tended to occupy a relatively distinct region compared with other myopathies. Hierarchical clustering identified Mild ( n = 9) and Severe ( n = 3) groups, which differed significantly in total mMS ( p = 0.009). Both groups showed fatty replacement in trunk muscles (including iliocostalis lumborum, longissimus, and external abdominal oblique) and adductor magnus, with relative sparing of sternocleidomastoid, infraspinatus, subscapularis, trapezius, rhomboid, and rectus femoris. Substantial asymmetry occurred only when both sides were affected. Total mMS showed no correlation with age at imaging or disease duration. Discussion: This study demonstrates that VCP myopathy exhibits a characteristic pattern of muscle involvement on whole‐body multi‐region assessment. Although clinical heterogeneity was observed, consistently affected trunk muscles and adductor magnus, which may be involved early after symptom onset, may provide supportive imaging clues when VCP myopathy is suspected.

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