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Regional Ischemic Immune Myopathy (RIIM)

Muscle fibers   Regional pathology: Varied involvement in different areas   Necrosis zone: In border regions between vessels   Purlieu zone: Region between vessels & necrosis zone   Regeneration zone: Clustered regeneration after necrosis Vessels   Capillaries: Necrotic (In areas with necrotic muscle fibers)   Veins with damaged walls NXP-2 antibody-related pathology MRI images

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Regional pathology: Necrotic areas

All tissues are involved
  Muscle fibers: Necrosis
  Capillaries: Necrosis
  Perimysial & endomysial connective tissue: Abnormal structure & CA9 staining

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H&E stain

Necrotic muscle fibers
  Clustered
  Pale stained or Hypercontracted
  No nuclear staining
  None have macrophage infiltration
Perimysium (Far right): Pale stained
Vessel Bundles (Arteries & Veins; Arrows): Not contiguous with necrosis zone

H&E stain

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H&E stain

Regional Necrosis

H&E stain

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RIIM: Borderzone Necrosis

C5b-9 (Green) & Collagen IV (Red) stains Regional necrosis   Zones of necrosis     Surrounding but not neighboring vessels (Arrow)     Do not respect fascicular borders   Necrotic muscle fibers     Clustered in borderzones between large arteries & veins (Arrows)     Muscle fiber cytoplasm: Stains for C5b-9 complement (Green; Above)   Connective tissue (Perimysium & endomysium) is also damaged     CA9: Abnormal staining of perimysial & endomysial connective tissue & muscle fibers(Below)     C5b-9 complement: Punctate deposition in perimysium (Above)   Capillaries, endomysial: Necrotic & effaced Purlieu zone: Muscle fibers between vessels & necrotic zone have no C5b-9 deposition Vessels (Arrows): Inside purlieu zone & Distant from necrotic zone

CA9 stain CA9 staining in necrotic zone: Abnormal on perimysium & endomysium

C5b-9 (Green) & Collagen IV (Red) stains Borderzone regions of necrosis: No relation to fascicular borders C5b-9 stain H&E stain Muscle fibers in Necrotic zones   General: Most in similar, early stage, of necrosis     Pale staining or Hypercontracted     No nuclear staining   Edges: Some are invaded by phagocytic cells H&E stain H&E stain Esterase stain Necrotic muscle fibers: Absent SDH staining SDH stain Necrotic muscle fibers: Reduced or Absent NADH staining NADH stain Muscle fibers in Necrotic zones Terminal components of complement ((C5b-9; Membrane attack complex)   C5b-9: Deposited in cytoplasm of clusters of necrotic muscle fibers Toluidine blue stain Necrotic muscle fibers   Myofiber cytoplasm shows     Loss of myofibrillar apparatus     Granular debris     Lipid droplets Electron microscopy RIIM: Capillaries Capillary, Endomysial: RIIM   Small & Necrotic with Effaced architecture (Open arrowhead) Electron microscopy Capillary, Endomysial: Control   Normal lumen contains RBCs Electron microscopy RIIM: Larger Vessels H&E stain Vein (Arrow)   Wall is pale, thickened & cellular Esterase stain Vessel   Surrounded by histiocytes Perimysial connective tissue   Contains histiocytic cells VvG stain Vein   Wall is pale, thickened & cellular   Endothelial cells: Large VvG stain RIIM vessels   Veins (v) have swollen endothelial cells, thickened walls, intramural inflammatory cells & damaged elastic lamina   Arteries (a) are normal Compare to: Control vessels VvG stain Normal   Artery (a)   Vein (v) VvG stain RIIM Vein (v)   Smooth muscle actin (Green): Multifocal loss (Arrows)   PECAM1: Remains present around vein Artery (a): Normal wall structure Smooth muscle actin (Green) & PECAM1 (Red) stains Regional Ischemic Immune Myopathy Purlieu zone: Between Vessels & Zone of necrosis H&E stain Muscle fibers   Varied size   Internal architectureL Irregular or Vacuoles   Aggregates: Caveolin & LC3 aggregates H&E stain   Cytoplasmic Aggregates: Caveolin & LC3 Caveolin-3 stain Endomysial Capillaries: C5b-9 deposition C5b-9 stain Regional Ischemic Immune Myopathy Muscle fiber regeneration zone H&E stain Regenerating muscle fibers: Small; Coarse internal architecture; Large nuclei; Clustered; In similar stages VvG stain ATPase pH 4.3 stain Immature muscle fibers   Many type 2C (Intermediate-stained) muscle fibers (Above)   Dark stain & Coarse internal architecture on NADH (Below) NADH stain Immature muscle fibers: Cytoplasm of all fibers stained by alkaline phosphatase Alkaline phosphatase stain Immature muscle fibers & related structures   Myofibers: Small (Black arrowheads) with excessive sarcolemmal folds (Inset)   Endomysium: Widened   Capillaries: Large with disrupted architecture (Open arrowhead) Toluidine blue stain Capillary: Regenerating zone   Markedly enlarged   Disrupted architecture   Endothelial cytoplasm (E): Swollen; Extended   Red blood cells (Black arrows): Extravasated Electron microscopy Regional Ischemic Immune Myopathy (RIIM): MRI T2: No contrast   Patchy regions of muscle & connective tissue pathology: Increased T2 signal Return to Neuromuscular Home Page Return to Inflammation Return to Inflammatory myopathies 9/2/2020