case_images: PMC11251991_01
case_images: During the second admission, the patient had mild atrophy of the lingual muscles (A), severe atrophy of both forearms (B), upper arms (C), and trapezius muscles (D) with concomitant shoulder collapse (E), with preserved muscle volume in both lower extremities (F) (white arrows).
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case_images: PMC11251991_01_fimmu-15-1378130-g001.jpg
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case_images: We reassessed the patient and found mild atrophy of the lingual muscles ( Figure 1A ), asymmetric involvement of the scapular winging ( Supplementary Figure 1 ), worsening of amyotrophy ( Figures 1B-F ) and decreased strength of the quadriceps (MRC grade 4).
case_images: The muscles of the tongue showed mild lipoatrophy [(A), green arrows]. Both the upper arm and forearm muscles exhibited bilateral asymmetric edema and lipoatrophy (B, C). Edema was observed in the right biceps, lateral femoral, and gastrocnemius muscles (orange arrows) (D). Atrophy was present in the trapezius and psoas muscles (E). Severe fat replacement was noted in the dorsal muscles (F, G). The volume of muscle in the lower extremities was preserved, with only slight involvement of the lateral group of thigh muscles compared to the posterior group of calf muscles (H, I). T1-weighted imaging: green arrow; short-tau inversion recovery (STIR) MRI: orange arrow.
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case_images: PMC11251991_01_fimmu-15-1378130-g002.jpg
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case_images: MRI was performed, revealing diffuse edema in the patient's upper arms and forearms bilaterally in short tau inversion recovery MRI. Mild edema was also observed in the patient's right lateral femoral and gastrocnemius muscles (see  Figure 2 ). MHC-I staining can be observed widely positive expression on myofibre membranes ( Supplementary Figure 2 ). Metabolism myopathy was ruled out through oil red and glycogen staining.
case_images: In the HE staining, numerous foci of inflammatory cells were observed in the muscle tissue [(A, B), red and yellow arrows]. Immunohistochemical staining revealed that the foci were mainly composed of CD20+ B cells (C) and CD68+ macrophages (D), accompanied by some CD138+ plasma cells (I) and a small number of CD4+ and CD8+ T cells (E, H). Additionally, some myofibers exhibited heterogeneous NADH enzyme activity (F), and C5b-9 was observed beneath the membrane of certain muscle fibers (G).
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case_images: PMC11251991_01_fimmu-15-1378130-g003.jpg
case_images: f3
case_images: A muscle biopsy was conducted on the patient's biceps muscle to investigate the potential presence of myogenic damage.  Figure 3  illustrates the presence of numerous foci of inflammatory cells distributed within the muscle bundles, accompanied by a large number of necrotic and regenerating muscle fibers, moderate connective tissue hyperplasia, and mild fat cell replacement, as evidenced by hematoxylin and eosin (HE) staining.