PMC9795206_01
Evolution of CPK and ASAT after three plasma exchange cycles (red arrows). The natural evolution of CPK and ASAT levels before initiation of plasmatic exchanges is symbolized by red arrows. As illustrated, three plasmatic exchanges led to a significant decrease in both CPK and ASAT levels.
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The patient underwent three sessions of apheresis on alternative days (see  Figure 1 ).
(A) Magnetic Resonance Imaging (MRI) of muscles of lower limbs, T1 Coronal and T2 axial reconstruction. MRI shows pathological bilateralhypersignal of proximal muscles: gluteal muscles, medial gastrocnemius muscles, solar muscles with relative respect of semitendinosus muscles. (B) Immuno-histo-chemical staining of the muscle biopsy. Standard muscle biopsy stain exhibiting muscle atrophy, degeneration, necrosis, macrophagic infiltration and muscle fiber irregularity.
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This was compatible with muscular oedema, specifically involving the medial gastrocnemii and solaris muscles (see  Figure 2A ). This revealed a muscle inflammation with macrophage infiltration, fibrillary involution and necrosis of myocytes, thereby confirming the diagnosis of necrosing myositis (see  Figure 2B ).