P.94 Clinical and pathologic features of clinically diagnosed inclusion body myositis (IBM) patients in Korea

Abstract

Inclusion body myositis (IBM) is a slowly progressive skeletal muscle disease occurring primarily in elderly patients. Recently, increased incidence of IBM has been reported in the East Asian population. The 2011 European Neuromuscular Centre (ENMC) criteria emphasized specific clinical features of weakness in finger flexion and knee extension. In this study, we reviewed the general features of IBM patients from Korean populations, classified by 2011 ENMC clinical criteria. We reviewed cases of IBM in Pusan national university Yangsan hospital. Eighteen cases were enrolled. Mean onset age was 63.4 years, half of the patients were male. Six of them were probable IBM, nine were clinically definite IBM, and two were clinically definite, but did not fit to pathological criteria. Eight patients were initially diagnosed as polymyositis, and two cases as amyotrophic lateral sclerosis. Mean duration of onset to diagnosis was 4.9 years. Most common initial presentation was difficulty in climbing up stairs, followed by hand grip weakness. Nine cases presented asymmetric clinical feature. Most of them showed myopathic pattern on needle electromyogram (EMG). Muscle biopsy revealed endomysial inflammation or rimmed vacuole in fifteen cases, but two cases showed non-specific chronic myopathic change without IBM specific pathologic findings. Thigh and forearm muscle atrophy was dominant in skeletal muscle computed tomography. Seven of fifteen cases (47%) revealed positive result to anti-cN1A antibody test. Eight patients showed no response to corticosteroid, five patients responded to corticosteroid partially. IBM is still considered a challenging disorder. In this study, we presented clinical features, imaging findings, muscle specific antibody result and pathological findings of clinically diagnosed Korean IBM patients. Awareness of IBM in Asian population is required as the cases are increasing in Asian countries.