G.P.81: A clinical point of view diagnosing juvenile idiopathic inflammatory myopathies without skin manifestations

Abstract

Juvenile idiopathic inflammatory myopathies (IIMs) are a rare group of systemic autoimmune disorders characterized by chronic skeletal muscle inflammation of unknown causes, with onset under 18years. IIMs all but juvenile dermatomyositis are extremely rare and poorly recognized, therefore often misdiagnosed as muscular dystrophy. Then we performed retrospective analysis in 6 patients with IIMs without skin involvement. All 6 patients had high levels of serum creatine kinase (2000–13,000U/L), symmetrical and proximal dominant muscle weakness. Two patients had high levels of creatine kinase levels in their asymptomatic period, but once muscle weakness developed, progression was relatively rapid compared to muscular dystrophy. All patients had fibrillation potentials and positive sharp waves in needle electromyography. Skeletal muscle MRI imaging of lower legs on STIR exhibited high signal intensity lesions with various degree. On muscle biopsy, consistent findings were necrotic and regenerating changes with minimum to mild inflammatory cellular infiltrations, then we could not confirm the diagnosis of IIMs only in their biopsy findings. Immunosuppressive therapy including steroid, methotrexate, cyclosporin and intravenous immunoglobulin showed efficacy in all patients. Our observation demonstrates that the comprehensive and detailed analysis of both clinical and laboratory findings could lead to the diagnosis of IIMs. Because IIMs are treatable disease, early and prompt diagnosis is highly recommended.