PMC6614968_01
(a) T1-weighted and (b) short tau inversion recovery (STIR) sequences showing edema (hyperintense areas on STIR, white arrows) in the proximal thigh muscles, characteristic of an inflammatory myositis.
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Magnetic resonance imaging (MRI) of the patient's pelvis revealed extensive edema throughout the proximal pelvic musculature with a symmetric distribution consistent with myositis (Figure 1).
Hematoxylin and eosin-stained frozen section (400x magnification) of the vastus lateralis revealing marked fiber size variation with necrotic (black arrows) and regenerating (white arrows) myofibers consistent with a necrotizing autoimmune myositis.
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Furthermore, an electromyogram and nerve conduction study demonstrated diffuse and active irritable myopathy, and a muscle biopsy of the vastus lateralis revealed necrotizing myopathy with minimal inflammatory infiltrate and MHC1 immunostaining consistent with NAM (Figure 2).
MRI T2-weighted sequence with hyperintense signal involving the occipital (arrows) and parietal lobes bilaterally, suggestive of posterior reversible encephalopathy syndrome.
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Consultation with neuroradiology suggested that the patient's neurological findings were consistent with PRES (Figure 3), suspected to be related to a delayed reaction to IVIG therapy.