[A case of microscopic polyangiitis with severe cardiac and respiratory muscle involvement]

A 66-year-old female was admitted to our hospital in January, 1998, complaining of low grade fever and muscle weakness of her legs. Physical examination revealed muscle weakness of her neck (4/5) and proximal skeletal muscles of her bilateral legs (3/5-4/5). She showed proteinuria and microhematuria. Her serum levels of ureanitrogen, creatinine, aspartate aminotransferase, alanine aminotransferase, creatinekinase, aldolase and myoglobin were all within the normal ranges. Antinuclear antibodies were negative, but her serum levels of pANCA (743 EU) and C reactive protein (18.0 mg/dl) were elevated. Neuroconduction velocity of her left common peroneal nerve was decreased to 40.8 m/sec and electric myograph showed neurogenic changes. Magnetic resonance images (MRI) of her bilateral thigh depicted high signal intensity in quadriceps by T 2 weighed images, but the signals were not enhanced by gadolinium injection. Muscle and renal biopsies revealed necrotizing vasculitis of the small arteries. Crescentic glomerulonephritis was also observed by renal biopsy. These findings supported the diagnosis of microscopic PN. On 16 th admission day, she developed acute cardiac and respiratory failures due to cardiac and respiratory muscle involvements with PN, and was assisted by mechanical ventilation. She was treated with methylprednisolone pulse therapy (500 mg/day, three consecutive days) on 18 th admission day, followed by 40 mg of oral prednisolone daily. However, her symptoms deteriorated, and herserum creatinine levels increased to 2.4 mg/dl. On 24 th admission day, intravenous cyclophosphamide pulse therapy (500 mg/day) was instituted. Her cardiac wall motion on echocardiography and serum creatinine levels gradually improved, but her skeletal and respiratory muscle weakness did not improve. On 38 th admission day, she was complicated with respiratory infection by methicillin resistant Staphylococcus aures. On 62 th admission day, she died of endotoxic shock. This is the first report describing respiratory muscle involvement with PN, and the second report describing MRI findings of muscle involvement by PN. Therefore, our case provides important clinical information for the diagnosis and treatment of the disease.