Clinical and pathological analysis of limb-girdle muscular dystrophy type 2B misdiagnosed as polymyositis

Objective To diagnose and differentially diagnose limb-girdle muscular dystrophy type 2B(LGMD2B)and polymyositis (PM) based on clinical and pathological characteristics. Methods Muscle biopsics were obtained from 8 patients suspected with LGMD2B who were initially diagnosed with PM.The clinical and pathological data from 8 cases of LGMD2B and 4 cases of PM by using histo-and immunohistochemistry with anti-dysferlin,dystrophins,sarcoglycans,MHC-Ⅰ,CD8 monoclonal antibodies were compared.Results (1) LGMD2B and PM shared similar pathological presentations including muscle fibet degeneration and necrosis in various degree,proliferation of connective tissue,and inflammatory cell infiltration.Normal stains of dystrophins and sarcoglycans were observed.whereas absent or very faint staining of dysfedin observed in muscle biopsies of 8 patients confirmed the diagnosis of LGMD2B.while normal stains of dysferlin on sarcolemma were observed in the 4 cases of PM.MHC-Ⅰ was weakly expressed or absent in LGMD2B.while strongly expressed on sarcolemma in PM and the infiltration area of inflammation cells.The expression of CD8 on a few inflammatory cells were positive in LGMD2B.while some inflammatory cells were positive in PM.(2)Both LGMD2B and PM shared similar presentation,including proximal muscle weakness,remarkable elevation of CK,myopathic changes in electromyography.Patients with LGMD2B did not complain of apparent muscle pain.and their erythrocyte sedimentation rate and Creactive protein were in normal range.which could be used as marker to differentiate from patients with PM.Conclusions Clinically and pathologically LGMD2B and PM are presented similarly and likely to be misdiagnosed.The absence of dysferlin in LGMD2B and high expression of MHC-Ⅰ and CD8 in PM are the key index of the diagnosis and differential diagnosis between LGMD2B and PM. Key words: Muscular dystrophies,limb-girdle; Polymyositis; Diagnosis,differential; Membrane proteins; Muscle proteins; Major histocompatibility complex; Antigens,CD8