Neuromuscular

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

Inclusion Body Myositis (Subtype)

Pathology features

Inflammation
  Focal invasion
  Immune Cell types
  Endomysial inflammation
Muscle fibers
  Aggregates
    Histochemistry
      AMPDA
      Cytoplasmic
      Eosinophilic
    Components
      αB-crystallin
      β-Amyloid
      Desmin
      LC3
      p62
      SMI-31
      TDP-43
      Ubiquitin
      VCP
    Ultrastructure
  Focal invasion
  MHC Class-1 expression
  Mitochondrial pathology
  Myopathy
  Myonuclei
  Vacuoles
Capillaries

Variant syndromes
  IM-VAMP in HIV
  PM-Mito

Gomori trichrome stain
IBM (IM-VAMP): Myopathy; Inflammation; Aggregates & Vacuoles


IM-VAMP (IBM): Muscle Pathology

IBM: Myopathic features


H & E stain

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
Vacuoles

2C fibers (Intermediate-stained): Common

ATPase pH 4.3 stain

Alkaline phosphatase stain: Often normal

Alkaline phosphatase stain

IBM: Inflammation & Focal invasion of Muscle fibers


Endomysial inflammation


H&E stain
Endomysial inflammation
  Most cells are lymphocytic
  Minority of cells are histiocytic (Acid phosphatase +)
  Some whole immune cells are focally invading muscle fibers (Arrow)

Acid phosphatase (Blue) stain

 
Gomori trichrome
Inflammatory cells in Endomysium

Gomori trichrome

Inflammatory cells in endomysium

Congo red

Inflammation: Endomysial & Perimysial
  Focal invasion of some muscle fibers by cells

H & E stain
Inflammation: Endomysial
  Focal invasion of some muscle fibers (Dark arrow)
Partially fused (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


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)

Muscle fibers replaced by immune cells

VvG stain

IM-VAMP (IBM): Lymphocyte Types

CD4
CD4 cells: Present in foci & Scattered in endomysium

CD8
CD8 cells: More in foci than in other endomysial regions

IM-VAMP: Mononuclear cell types
  CD4 & CD8 cells
    Present in endomysial lymphocyte foci
    CD8 cells
      Location
        Endomysial cell foci
        Focal invasion of muscle fibers
      Terminally differentiated (TEMRA) phenotype
        Loss: CD28
        Upregulation: Killer cell lectin-like receptor G1 (KLRG1) & CD57
        Cytotoxic potential: Perforin; Granzyme B; KLRG1
        Limited proliferative capacity
        May produce IFN-γ
        Large granular lymphocytes (LGLs; CD3+, CD8+, CD57+, CD244+, CD28-, Kv1.3+)
        Clinical association: Large granular lymphocytic (T-LGL) leukemia
    CD4 cells
      Scattered: In endomysium between muscle fibers
      CD4+CD28(null) T cells: Endomysial cell foci; Proinflammatory & Cytotoxic
    T cell receptor (TCR) Vβ repertoire: Restricted (Clonal expansions); Similar to changes seen in blood
  Histiocytic cells
    Scatttered: In endomysium
    Clusters: In endomysial regions of focal invasion of muscle fibers by cells
  B-cells: NOT present in cell foci


CD8 stain
CD8 cells: In endomysial cell foci in IM-VAMP

IBM: Vacuoles (or Inclusions)




Congo red stain

Congo red stain

Congo red stain

Congo red stain

Vacuoles

Gomori trichrome stain

 

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

Gomori trichrome stain

Gomori trichrome stain


Gomori trichrome stain
Vacuoles & Cytoplasmic bodies

Gomori trichrome stain

Atypical vacuoles: Contain irregular green-stained material

Gomori trichrome stain

Gomori trichrome stain


IBM
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

IM-VAMP: Amyloid
Vacuoles may contain amyloid-like birefringent (red-green) material (Congo red stain)

Alcian blue/Nuclear fast red

IBM: Aggregates

Aggregates: General features in IBM-like disorders

Aggregates: Histochemistry


Cytoplasmic Aggregates
  Dark, eosinophilic hyaline appearance (Arrows)
Cytoplasmic Aggregate
  Large
  Near irregular vacuoles

H&E stain

H&E stain

VvG stain

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

Gomori trichrome stain

Gomori trichrome stain


AMPDA 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 + Congo red stains

SMI-31 staining in some nuclei

SMI-31 + Congo red stains

αB-crystallin
  • 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)

TDP-43 aggregates

TDP-43
 
Congo red + TDP43
TDP-43: IBM
  • 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)

p62 aggregates

p62 stain

p62 stain

LC3 aggregates

LC3 stain

LC3 stain


LC3 stain
LC3: IBM

 


Congo red + LC3 stain


Desmin stain
IBM: Desmin stain: Patterns
  Diffusely in cytoplasm of iommature muscle fibers
  Irregular aggregates in scattered muscle fibers
  Localized at site of focal invasion of a muscle fiber (below)

Desmin stain

IM-VAMP: Ultrastructure
Focal invasion of muscle fibers by cells
Aggregates & Inclusions, Cytoplasmic


IM-VAMP: Muscle fiber pathology + Focal invasion of Muscle fiber by cells
  Cytoplasmic inclusions: Several types
    Myeloid
    Membrane-like
    Tubulo-Vesicular
    Filamentous
    Autophagic debris
    Lipid-like bodies
    Mitochondria
Endomysial capillaries
  Normal size & walls


Inclusions: Different Types in muscle fibers in IM-VAMP
  Filamentous (Black arrow)
  Osmophilic (Red arrow): Possible remanants of nuclear membranes
  Membrane-like (White arrow): Multilayered; Irregular shapes; May be within larger, "vacuolar", structures
  Tubulovesicular material (Below)

From: R Schmidt


From: R Schmidt
Aggregates contain
  Filaments
  A few myeloid structures & mitochondria

From: R Schmidt
Aggregates contain
  Filaments
  A few myeloid structures & mitochondria

From: R Schmidt


Aggregate Contents
  Filaments
  Myeloid structures


Tubulofilaments


Aggregates contain
  Filaments
  Myeloid structures
  Mitochondria



Aggregates contain
  Mitochondria


Muscle fibers: Focal Invasion by Cells

Inflammatory cells & Focal invasion of Muscle fibers in IM-VAMP (IBM)
  Lymphocyte, Large, Possibly Granular (Black Arrow)
    Extends a process (White arrow) into a non-necrotic muscle fiber
  Other lymphocytes & histiocytes
    Whole immune cells may be invading muscle fiber
    Present in extracellular regions around muscle fiber
Muscle fiber pathology: Aggregates, various types

Muscle fiber: Focal Invasion by Cell
  Lymphocyte, single, invades muscle fiber
  Lymphocyte location: Inside muscle fiber; Above sarcolemma; Neighbors myonucleus


Muscle fiber: Focal Invasion by Cells
  Lymphocytes (Light cytoplasm) & Histiocytes (Dark cytoplasm with phaogcytic debris)
    Within the muscle fiber
      Closely apposed to each other
    Also in extracellular space
  Sarcomeres near invading cells: Normal structure

Muscle fiber: Focal Invasion by small cell processes

Lymphocyte: Focal Invasion of a Muscle Fiber (Arrows)
  Muscle fiber structure is damaged


MHC-1 Expression


Normal

IBM
IBM: MHC Class-1 up regulation by muscle fibers

MHC Class I stain

MHC Class I stain
MHC Class I: Expression by muscle fibers
  Diffuse: Present in most, or all, muscle fibers
  Distribution
    Mostly Sarcolemma, or Sarcolemma + Cytoplasm

MHC Class I stain

Also see

IM-VAMP: Myonuclear Pathology


IM-VAMP: Nuclear features
  Location: Internal nuclei
  Structure
    Clear centers
    Outlines: Smudged or Pale


H&E stain
IM-VAMP: Nuclei
  Internal: One or Several
    Structure: Clear centers
    May have peripheral cytoplasmic halo

Gomori trichrome stain

Gomori trichrome stain

IM-VAMP Myonuclei: Smudged outlines or Clear centers

Congo red stain
Myonuclei
  Indistinct borders
  Irregular shapes

H&E stain

H&E stain
IM-VAMP Myonuclei: Smudged outlines; Pale staining (Arrows)

H&E stain


IM-VAMP Myonuclei: Reduced staining in subsarcolemmal regions of muscle fibers

H&E stain

H&E stain

IM-VAMP (IBM): Mitochondrial pathology

Mitochondrial DNA (mtDNA) Deletions & Duplications 3

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

Cytochrome oxidase stain


COX stain
COX-negative muscle fibers
  2 muscle fibers with nearly absent staining
  Neighboring fibers have normal staining
  Changes are likely due to acquired mutations in mtDNA causing loss of synthesis of COX subunits


SDH stain
SDH-positive muscle fibers
  2 muscle fibers with increased staining
    Small muscle fiber above shows increased staining in entire cytoplasm
    Larger muscle fiber below has more mitochondrial accumulation in subsarcolemmal regions
  Neighboring fibers have normal staining
  Changes are likely due to acquired mutations in mtDNA causing mitochondrial proliferation

Ultrastructure: Subsarcolemmal Mitochondrial Accumulation

From: R Schmidt

From: R Schmidt

From: R Schmidt

From: R Schmidt

From: R Schmidt

Mitochondria: Abnormal morphology

From: R Schmidt

From: R Schmidt

From: R Schmidt

Also see: Myositis (IM-VAMP) with Mitochondrial Pathology

IBM: Capillary Proliferation & Enlargement


VvG stain

VvG stain
Endomysial Capillaries: Large; Increased numbers

Ulex stain

Ulex stain

Ultrastructure: Cells near Endomysial Capillaries

From: R Schmidt

From: R Schmidt

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References
1. Brain 2019 Jul 20
2. Brain 2016;139:1348-1360, Brain 142:2590–2604
3. Brain Pathol 2020 Dec 22;e12931
4. Ann Neurol 2022 Jan 22
5. J Neuropathol Exp Neurol 2022;81:825-835

5/9/2023