Dermatomyositis perifascicular pattern of involvement For instance: Dermatomyositis perifascicular pattern of involvement perimysial > endomysial inflammation Polymyositis CD8 (+) cytotoxic T-cell infiltration perimysial < endomysial inflammation IBM rimmed vacuoles mitochondrial abnormality (secondary)
PM – multifocal endomysial inflammation
PM – CD8 (+) cytotoxic T-cells infiltration
Dermatomyositis perifascicular pattern of involvement For instance: Dermatomyositis perifascicular pattern of involvement perimysial > endomysial inflammation Polymyositis CD8 (+) cytotoxic T-cell infiltration perimysial < endomysial inflammation IBM rimmed vacuoles mitochondrial abnormality (secondary)
IBM - RVs
IBM – RVs + “ Inclusions “
“ Change in protein hometostasis ” Congophilic amyloid: TDP-43; Ab40,42; a-synuclein; phosphorylated proteins including tau; P62; LC3; a-B crystalline; others. “ Change in protein hometostasis ”
ELECTRON MICROSCOPY, 15-20 nm FILAMENTS
Immunohistochemical evidence of MHC class I upregulation Morphological hallmark of autoimmune myopathies Degenerating/Necrotic fibers Regenerating fibers Myofiber atrophy Evidence of inflammatory infiltration + Distinctive histological features suggesting different pathophysiological mechanisms underlying each disease + Immunohistochemical evidence of MHC class I upregulation
MHC class I (HLA-A,B,C) immunostaining
Idiopathic myopathies Dermatomyositis (DM) Polymyositis (PM) Inclusion body myositis (sIBM), sIBM-like syndrome Immune-mediated necrotizing myopathies (IMNM)
Anti-HMGCR Anti-tRNA synthetase Liang C , Needham M. Necrotizing autoimmune myopathy. Curr Op Rheumatol 2011, 23:612-619 (modified by KT 2018)
Histology pictures of PF’s case a-SRP Ab(+) Histology pictures of PF’s case MHC class I
Case 2 a-HMGCR Ab(+)
MHC class I
Summary of myopathy with a-Signal Recognition Particle antibody Clinical spectrum: broad. [Suzuki S, et al: OJRD 2015; 10: 61- 70.] 100 patients with inflammatory myopathy and a-SRP Ab - mean age at disease onset 51.3+/- 19.3 ( <15 years old, 8%), anticedent infection (7). Pathology: necrotizing myopathy (84) >> non-specific myositis (14) > PM/DM (2). Factors for poor outcome: pediatric disease onset (the only independent factor a/w poor prognosis by multivariate logistic analysis); severe limb weakness; dysphagia, muscle atrophy; elevated C-reactive protein. - interstitial lung disease: no correlation with poor outcome. Treatment: in addition to prednisolone, the majority(77%) of necrotizing myopathy patients required additional immunotherapy ( eg. IVIg, IV methyl-prednisolone, tacrolimus, azathioprine, cyclosporine, cyclophosphamide, plasma exchange)
THE END Have a pleasant day !