PMC7325302_01
Histopathology from muscle biopsy at time of initial diagnosis. a Haematoxylin and eosin stain demonstrating a pale necrotic fibre (arrow). b Haematoxylin and eosin stain demonstrating a basophilic regenerating fibre (arrow). c MHC class I stain demonstrating patching upregulation of MHC class I. d CD68 stain demonstrating a necrotic fibre infiltrated by macrophages
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Fig1
Initial creatine kinase (CK) was approximately 6000 iU/L, and single fibre necrosis, predominantly macrophagic inflammation with upregulation of major histocompatibility complex (MHC) Class I at the periphery of fibres and regeneration suggestive of necrotising myopathy was identified on the needle muscle biopsy of the quadriceps muscle (Fig. 1).
Disease course with creatine kinase levels and treatment
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Fig2
Her CK, which had peaked at 10,527 iU/L 15 months from the onset, had fallen to 658 iU/L after 9 months of prednisolone treatment when methotrexate was introduced (Fig. 2).
PMC7325302_02
MRI thighs pre- and post-rituximab therapy. Axial a T1-weighted FSE and b STIR images of the upper thighs in May 2018 showing patchy oedema within the bilateral vasti, adductors and hamstrings. Signal abnormality in the left vastus lateralis is most conspicuous (white arrow). Subsequent axial c T1-weighted FSE and d STIR images of the same region in March 2019 demonstrate complete resolution of oedema. Muscle bulk remains normal on both studies with no fatty infiltration
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Fig3
A repeat MRI muscles 3 months after second course of rituximab showed resolution of muscular oedema (Fig. 3, panel C & D), with corresponding clinical and biochemical improvement (CK 600 iU/L).
PMC7325302_03
MRI thighs pre- and post-rituximab therapy. Axial a T1-weighted FSE and b STIR images of the upper thighs in May 2018 showing patchy oedema within the bilateral vasti, adductors and hamstrings. Signal abnormality in the left vastus lateralis is most conspicuous (white arrow). Subsequent axial c T1-weighted FSE and d STIR images of the same region in March 2019 demonstrate complete resolution of oedema. Muscle bulk remains normal on both studies with no fatty infiltration
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Fig3
A repeat MRI muscles 3 months after second course of rituximab showed resolution of muscular oedema (Fig. 3, panel C & D), with corresponding clinical and biochemical improvement (CK 600 iU/L).