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

Inclusion body Myositis Subtype

  Focal invasion
MHC Class-1 up-regulation
Mitochondrial changes

Also see: PM-Mito

IBM: Myopathic features

H & E stain

H & E stain
Myopathy: Chronic; Ongoing
  • Muscle fiber size: Varied
    • Small fibers
      • Shape: Rounded or Polygonal
      • May occur in clusters
      • May be basophilic
    • Large fibers: May be hypertrophied
  • Muscle fiber morphology
    • Internal nuclei: In scattered muscle fibers
    • Internal clear regions: Irregular shape; Possibly vacuoles
  • Endomysial connective tissue: Increased in some regions

Fiber size: Varied
Focal invasion by cells

2C fibers (Intermediate-stained): Common

ATPase pH 4.3 stain

Alkaline phosphatase stain: Often normal

Alkaline phosphatase stain

Cytochrome oxidase (COX): Some patients have scattered COX- muscle fibers

Cytochrome oxidase stain

IBM: Inflammation & Focal invasion

Endomysial inflammation

Endomysial inflammation
  Most cells are lymphocytic
  Minority of cells are histiocytic (Acid phosphatase +)
  Some cells are focally invading muscvle fibers

Acid phosphatase (Blue)

Inflammation: Endomysial & Perimysial
  Focal invasion of some muscle fibers

H & E stain
Inflammation: Endomysial
  Focal invasion of some muscle fibers (Dark arrow)
Split muscle fiber (Light arrow)

H & E stain

H & E stain

Esterase stain

Acid phosphatase stain

Acid phosphatase stain
Focal invasion of muscle fibers
  • Inflammatory cells invade a focal region of the muscle fiber (arrows).
  • Other regions of the muscle fiber appear intact.
  • Some cells invading the muscle fiber are CD8+ T-cells.
  • Occasional cells are macrophages & stain with acid phosphatase.

CD4 stain

CD3 stain

Gomori trichrome
Inflammatory cells in endomysium
  • Linear distribution of cells between muscle fibers (Left)
  • Larger collections of cells around muscle fibers (Right)

Congo red

Acid phosphatase

Acid phosphatase
  • Cells around vessel (Left) are mostly T-cells (unstained)
  • Cells near and within muscle fibers (Right) contain more macrophages (Stained red)

Mononuclear cell types
  CD4 & CD8 cells are present in endomysial foci
  Individual CD4 cells are scattered in the endomysium between muscle fibers



IBM: Vacuoles (or Inclusions)

Congo red stain

Congo red stain

Congo red stain
  • Muscle fibers with several rimmed vacuoles (arrows)
  • Vacuoles contain
    • Congo red: Blue amorphous, granular material (Above right; Below)
    • Gomori trichrome: Red-stained material
    • VvG: Gray-stained material
  • Nuclei: Some are near vacuoles or enlarged
  • Amyloid in some vacuoles
    • Visualized with polarized light (Above left (Red) & Below)
    • Small foci of red stained amyloid (arrows) are in, or around, vacuoles
  • Some muscle fibers also contain
    • Cytoplasmic bodies or inclusions (Above right; VvG stain below)
  • Differential diagnosis: Vacuoles

Gomori trichrome stain

Gomori trichrome stain
IBM: Vacuoles
  One, or several, in a muscle fiber
  Shapes: Irregular
  Some contain red-staining material

Gomori trichrome stain

Vacuoles & Cytoplasmic bodies

Gomori trichrome stain

Atypical vacuoles: Contain irregular green-stained material

Gomori trichrome stain

Gomori trichrome stain

More vacuoles
  • Another muscle fiber with vacuoles (Left; Congo red stain)
  • Vacuoles in 2 muscle fibers (Right; Toluidine blue stain)
    • Vacuoles may be in large or small fibers
    • Vacuoles may contain autophagic debris, or 15 to 18 nm filaments

Vacuoles may contain amyloid-like birefringent (red-green) material (Congo red stain)
  • Muscle fiber with large vacuole (Left)
  • Birefringence: Red-Green material in vacuole (Middle & Right)

IBM: Aggregates

Aggregates: General features in IBM-like disorders

Aggregates: Histochemistry

  Dark, eosinophilic hyaline appearance

H&E stain

H&E stain

Basophilic cytoplasmic aggregates
  Indistinct borders
  ? Degenerated nuclei

H&E stain
  Near iregular vacuoles

VvG stain

Cytoplasmic bodies
  Small, dark-stained structure
  May be several in individual fibers
  Present in fibers without vacuoles

Gomori trichrome stain

AMPDA aggregate
  Present in aggregated material in muscle fiber cytoplasm
  Some, but not most, aggregated material surrounds vacuoles

AMPDA stain

AMPDA stain

SMI-31 positive aggregates in IBM

SMI-31 + Congo red stains

Congo Red + Fluorescence with Texas red filter
  • IBM (Top Left; Bottom): SMI-31 staining in several patterns
    • Aggregates in the cytoplasm of muscle fibers with no vacuoles
    • Occasional small aggregates scattered around the rim of some vacuoles
    • Some aggregates near nuclei
    • Diffuse increase in cytoplasm of some muscle fibers
  • IBM (Right): No fluorescence of vacuoles or aggregates in muscle fibers for amyloid
  • SMI-31 aggregates are not usually present in PM-Mito biopsies

SMI-31 + Congo red stains

SMI-31 + Congo red stains

SMI-31 staining in some nuclei

SMI-31 + Congo red stains

  • IBM (Left): Clusters of αB-crystallin staining in muscle fibers
  • Normal (Right): No focal staining of muscle fibers

Ubiquitin conjugates: IBM
  • Focal dark staining
    • Staining may be present around rim of vacuoles (arrow)
    • Aggregates are also located in other regions of muscle fibers
  • Increased staining in much of the cytoplasm (right)

Valosin-containing protein (VCP): IBM
  • Focal dark staining
    • Aggregates are mostly small & scattered through muscle fibers
    • Some fibers, especially small, can have increased cytoplasmic staining
  • Occasional vacuoles have some VCP staining

Congo red + β-amyloid stain

Congo red + fluorescence
β-Amyloid: IBM
  • Small focal regions of dark staining (Left)
    • Aggregates are mostly small & scattered through muscle fiber
    • Some fibers, especially small, can have increased cytoplasmic staining
  • Regions of β-Amyloid do not show fluorescence with Congo red stain (Right)

Congo red + TDP43
  • Aggregates
    • Small focal regions of dark staining (Left; Above)
      • Aggregates are mostly small & scattered through muscle fiber
    • Large cytoplasmic TDP-43 aggregates (Right; Above)
  • Inflammatory cells (Below): TDP-43 stains inflammatory cells in
    • Endomysium
    • Regions of focal invasion of muscle fibers
  • TDP-43 aggregates are not present in PM-Mito biopsies
Congo red + TDP43

CD4 (Green) + TDP43 (Red)

TDP-43: Aggregates & Inflammatory cells in IBM
  • TDP-43 stains
    • Focal aggregates in muscle fibers (Red)
    • Inflammatory cells: Overlap with CD4 (Yellow)
  • CD4 also stains scattered endomysial cells without TDP-43 (Green)

SMI-31 (Green) + TDP43 (Red)

TDP-43: Aggregates and cytoplasmic staining with varied relation to SMI-31 staining
  • TDP-43 stains
    • Focal aggregates in muscle fibers: With (Yellow) and without (Red) overlap of SMI-31
  • SMI-31 also stains
    • Cytoplasm in some fibers without TDP-43 (Green)
    • Rim of internal nucleus (Green; Arrow) associated with neighboring TDP-43 staining (Red)

Congo red + LC3 stain
  • Focal regions of dark staining of varied shapes (Top)
    • Aggregates are cytoplasmic, small or large & have varied shapes
  • LC3 aggregates are also present in PM-Mito biopsies (Bottom), unlike SMI-31 or TDP-43

Congo red + LC3 stain

From: R Schmidt
Ultrastructure: Vacuoles contain tubulovesicular material




IBM: MHC Class-1 up regulation by muscle fibers
  • Normal (Left)
    • Staining of capillaries but not muscle fibers
  • IBM (Right & Below)
    • Up-regulation within, and on the surface of, muscle fibers.
    • MHC-1 is also present on inflammatory cells
    • Immature, smaller fibers can also express MHC Class-1 on their surface & in cytoplasm

Also see
Return to Neuromuscular Home Page
Return to Inflammation
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