Fig. 1

a and b STIR T2-weighted imaging of MRI in the left proximal upper extremity (a sagittal imaging; b axial imaging). Red and yellow arrows indicate the left biceps brachii muscle and triceps brachii muscle, respectively. c and d H&E staining at lower magnification (c) and higher magnification (d) of muscle biopsy from the right biceps brachii muscle. e Another field image of H&E staining of the muscle biopsy from the same muscle. Scale bars: 200 μm (c), 100 μm (d and e). Black arrows indicate a mixture of muscle fiber necrosis and regeneration without inflammatory cell infiltration. f Clinical course of the patient showing serum levels of creatine kinase (CK, normal, 41–153 U/L). IVIG: intravenous immunoglobulin. g Clinical course of the patient showing severe hypoxia and hypercapnia due to hypoventilation caused by weakness of respiratory muscles. BIPAP was used for the management of acute respiratory failure, which dramatically improved after the commencement of BIPAP support