G.P.75

We describe a 10-year old girl with progressive lower limb weakness and myalgia. With increased serum muscle enzymes, erythrocyte sedimentation rate, proximal muscle weakness, and EMG findings, she was considered as an inflammatory myopathy. Oral prednisolone (2 mg/kg/day) treatment was started. During clinical observation patient showed no response to treatment and muscle biopsy was performed. Muscle biopsy showed COX-negative fibers without discrete inflammatory infiltrates and necrotizing features. Mitochondrial DNA analysis did not reveal any mutation. The patient was diagnosed as “inflammatory myopathy with COX negative fibers” with these findings. Prednisolone dose was decreased and methotrexate (250 mcg/kg/week) was added to treatment. With recent therapy her complaints decreased dramatically. She has been well now for 3 years after diagnosis. The COX negativity and the presence of blue fiber in combined SDH-COX stains in inflammatory myopathy have been created some suspicions such as mitochondrial dysfunction may induce pathologic inflammatory response or an abnormal inflammatory response may be a contributory factor in mitochondrial dysfunction.