1. 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)

2. PM – multifocal endomysial inflammation

3. PM – CD8 (+) cytotoxic T-cells infiltration

4. 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)

5. IBM - RVs

6. IBM – RVs + “ Inclusions “

8. “ 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 ”

9. ELECTRON MICROSCOPY, 15-20 nm FILAMENTS

10. 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

11. MHC class I (HLA-A,B,C) immunostaining

12. Idiopathic myopathies
Dermatomyositis (DM)
Polymyositis (PM)
Inclusion body myositis (sIBM), sIBM-like syndrome
Immune-mediated necrotizing myopathies (IMNM)

13. Anti-HMGCR Anti-tRNA synthetase
Liang C , Needham M. Necrotizing autoimmune myopathy. Curr Op Rheumatol 2011, 23: (modified by KT 2018)

14. Histology pictures of PF’s case
a-SRP Ab(+)
Histology pictures of PF’s case
MHC class I

15. Case 2
a-HMGCR Ab(+)

16. MHC class I

17. Summary of myopathy with a-Signal Recognition Particle antibody
Clinical spectrum: broad. [Suzuki S, et al: OJRD 2015; 10: ]
100 patients with inflammatory myopathy and a-SRP Ab
- mean age at disease onset / ( <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)

18. THE END
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