Inflammatory Myopathies with Vacuoles, Aggregates & Mitochondrial Pathology (IM-VAMP)

Myositis with mitochondrial pathology (PM-Mito) subtype

• Mitochondrial pathology: 2% to 27% of muscle fibers
  • Cytochrome oxidase negative muscle fibers
  • SDH positive muscle fibers
  • Also see: Mitochondrial pathology
• Endomysial inflammation
• Focal invasion of muscle fibers by inflammatory cells
• mtDNA deletions (90%): Multiple
• Aggregates in muscle fibers: LC-3; αB-crystallin ⁵⁸
• No vacuoles or SMI-31 aggregates

INFLAMMATION: Predominantly Endomysial H&E stain Focal invasion of muscle fibers by immune cells H&E stain MYOPATHY   Muscle fiber sizes: Varied; Largewts fibers hypertrophied   Connective tissue, endomysial: Increased, mild to moderate IM-VAMP: MITOCHONDRIAL CHANGES Cytochrome oxidase (COX) negative muscle fibers Cytochrome oxidase stain Succinate Dehydrogenase (SDH) positive muscle fibers SDH stain

OTHER FEATURES
Perivascular Inflammation: Ocasional	MHC-I Upregulation on muscle fiber surface
LC-3 aggregates in muscle fibers