[A case with severe respiratory muscle weakness due to chronic myositis associated with PBC]

We report a 37-year-old woman with slowly developing muscular weakness for 2 years following insidious stiffness of calf muscle. Serum CK was elevated up to 4,207 IU/l. She presented sleepiness, weakness of proximal and truncal muscles and systemic muscular atrophy. While she had not experienced dyspnea, her arterial blood gas analysis revealed extreme hypoxia and hypercapnea due to weakness of respiratory muscles. Echocardiogram showed thinness and hypokinesis of left ventricular wall, and arrhythmia was pointed out by holter ECG. Needle elctromyogram of the proximal muscles exhibited polyphasic units with low amplitude. Muscle biopsy showed degeneration and necrosis of muscle fibers as well as regeneration. Mild infiltration of inflammatory cells was shown. Serological examination showed positive antimitochondrial M2 antibody, especially specific for primary biliary chirrhosis (PBC). She was diagnosed as chronic myositis associated with PBC. Four cases of idiopathic myositis with severe weakness of respiratory muscle, associated with PBC had been reported. These cases and our present case share the similar feature in respect of insidious or chronic course and resistance to therapy. In our present patient, respiration had been supported by BiPAP and she has been successfully improving slowly by oral steroid following 4 courses of methylprednisolone pulse therapy.