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

Inclusion body Myositis Subtype

MHC Class-1 up-regulation
Mitochondrial changes

Also see: PM-Mito

IBM: Myopathic features

H & E stain
Myopathy: Chronic; Ongoing
  • Muscle fiber size: Varied
    • Small fibers: Rounded or Polygonal; May occur in clusters
    • 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

H & E stain

Endomysial inflammation: Focal invasion of some muscle fibers (Dark arrow)
Split muscle fiber (Light arrow)

H & E stain

2C fibers are 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

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

Endomysial inflammation

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
  • 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

Congo red stain

Gomori trichrome stain

VvG 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

SMI-31 + Congo red stains

Congo Red + Fluorescence with Texas red filter
SMI-31 positive aggregates in IBM
  • 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
Return to Inflammatory myopathies & IBM