Neuromuscular

DERMATOMYOSITIS: Childhood & Adults 2
  Dermatomyositis with Vascular Pathology (DM-VP)

DM-VP
  Childhood
    Muscle fiber pathology
      Aggregates (LC3)
      Vacuoles
      MHC Class I
      Perifascicular atrophy
      Borderzone
      Epimysial
      Stains
        Gomori trichrome
        H&E
        NADH
        Mitochondrial
        Alkaline phosphatase
        MxA
        Toluidine blue
    Vessel pathology
      Capillaries, Endomysial
        H&E stain
        Alkaline phosphatase
        Complement deposition
        Endothelial stains
          Ulex
          Immunohistochemistry
         Ultrastructure
      Artery & Vein, Perimysial
        Damage
    Inflammation
  Variants
    Adult
    Child, Severe

DM syndromes, Other
  IMPP
  RIIM
Br J Child Dis 1912;9:247

Dermatomyositis with Vascular Pathology (DM-VP)
  Muscle fiber atrophy: Perifascicular (Border zone) distribution

Original Pathologic Description of Dermatomysitis with Vascular Pathology

Batten FE Br J Child Dis 1912;9:247

DM-VP: Perifascicular Muscle Fiber Smallness

  Atrophic Muscle Fibers: Near Avascular Perimysial Connective tissue (Dark arrow) surrounding fascicle
  Larger Muscle fibers: Within fascicle near intermediate sized perimysial vessels
  Vessel in Vascular Perimysium: White Arrow

H&E stain

Border-zone Muscle Fiber Pathology

Perifascicular Muscle Fiber Atrophy: Along Avascular Perimysium
Atrophic perifascicular muscle fibers neighbor a long region of avascular perimysium (Center).
Normal sized muscle fibers neighbor vascular perimysium (Sides).
Control: Vessels & Perimysium


H&E stain
Vessels & Vascular Perimysium: Within fascicle, Within region containing larger muscle fibers (Dark Arrow)
Avascular Perimysium: Neighbors small muscle fibers (Top & Left)

VvG stain
Vessels & Vascular Perimysium: Within fascicle, Within region containing larger muscle fibers (Dark Arrow)
Avascular Perimysium: Neighbors small muscle fibers (Surrounding perimysium)

Toluidine Blue stain
Vessels & Vascular Perimysium: Within fascicle, Within region containing larger muscle fibers (White Arrow)
Endomysial capillaries: Abnormal ATPase staining in areas near muscle fiber atrophy
Avascular Perimysium: Neighbors small muscle fibers (Surrounding perimysium) (Dark Arrow)
Small muscle fibers near edge of fascicle: Often type 2 or 2C

ATPase pH 4.3 stain
Atrophic perifascicular muscle fibers neighbor long regions of avascular perimysium.

Gomori trichrome stain
Atrophic perifascicular muscle fibers neighbor a long region of avascular perimysium.


H&E stain
Atrophic perifascicular muscle fibers have basophilic cytoplasm and large nuclei.
Some perifascicular muscle fibers have basophilic or eosinophilic aggregates

H&E stain
Perifascicular muscle fiber pathology: Cytoplasmic aggregates (dark staining) & Internal nuclei.

VvG stain

Perifascicular pathology: Other stains

NADH

NADH stain
Muscle fibers near avascular perimysium: Small & Stain darkly
Muscle fibers near vascular perimysium: More normal (Below, Arrow)

NADH stain
MHC Class I
  Upregulated at edges of fascicles near avascular perimysium.
  Less, or no, staining, near perimysium containing larger vessels (Arrows)

MHC Class I stain

Perifascicular atrophy: Toluidine blue-stained plastic sections

Muscle fibers: Atrophic in perifascicular regions; Irregular sarcolemmal membrane
Muscle fibers
  Size: Atrophic
  Sarcolemmal membrane: Irregular
  Contain lipid droplets
MITOCHONDRIAL PATHOLOGY
The extent of the perifascicular muscle fiber pathology in active DM is often more prominent on cytochrome oxidase stain.
SDH stain is not reduced.
Reduced cytochrome oxidase staining is not typically present in IMPP syndromes which have a different pattern of perifascicular muscle fiber pathology.
Cytochrome Oxidase

COX stain
Muscle fibers near avascular perimysium are small & have pale COX staining
Succinate Dehydrogenase

SDH stain
Muscle fibers near the avascular perimysium are small & have normal or dark SDH staining
Perifascicular muscle fibers near avascular perimysium: Small; Pale COX staining, Blue (SDH) color

COX + SDH stain
Mildy reduced COX stain in perifascicular muscle fibers with normal size. (Arrow; Right)

COX stain
Perifascicular atrophy: ATPase pH 9.4 stain

ATPase pH 9.4 stain
Perifascicular atrophy is often especially obvious on ATPase stains.
Small fibers: Both types I & II.
ATPase pH 4.3

ATPase pH 4.3 stain
Endomysial capillaries: Increased numbers stained in regions near areas of perifascicular atrophy (Arrows).

ATPase pH 4.3 stain


ATPase pH 4.3 stain
Endomysial capillaries: Increased ATPase staining
Type IIC muscle fibers (intermediate staining): Present in regions of atrophy & larger muscle fibers.
Type 1 muscle fibers: Few, or none, in regions of most severe atrophy at edge of fascicles (Above; Dark arrow).
Small muscle fibers: Located near avascular perimysium.
Fibers near intermediate-sized perimysial vessel (Below; White arrow): Larger size.

ATPase pH 4.3 stain
PAS

PAS stain
DM-VP: Increased glycogen staining in small perifascicular muscle fibers.1

Perifascicular muscle fiber atrophy: Fiber pathology

Muscle fibers in regions of perifascicular pathology show several abnormalities in addition to being small.
Some muscle fibers have
  Vacuolar or reticulated cytoplasm (Below).
  Cytochrome oxidase staining reduced
  MHC-I upregulation
  Aggregates: LC3 & Caveolin-3
Muscle fiber nuclei are enlarged.
Muscle fiber necrosis is rare.
 
H&E stain
Vacuoles in small & intermediate-sized muscle fibers

GT stain

Congo red stain
Als see: Secretory Autophagy
Muscle fibers may also have
  Coarse internal architecture with basophilia (Left, Arrow), or
  Internal nuclei (Right).
The abnormal internal architecture may be better visualized on Gomori trichrome
 
H&E stain
Abnormal internal architecture in dermatomyositis muscle fibers is more apparent on Gomori trichrome stains.
The abnormalities may be present in both small and large muscle fibers.
Cytoplasmic bodies may occur


 
Cytoplasmic bodies

GT stain
Autophagic Aggregates: LC-3 & Caveolin-3
Aggregates and increased cytoplasmic staining are common in perifascicular muscle fibers
with abnormal internal architecture in DM-VP.
 
Caveolin-3 stain

LC3 stain
LC-3 aggregates: More prominent in muscle fibers toward edge of fascicle
LC-3 aggregates: Irregular shaped in muscle fiber cytoplasm

AMPDA stain
Aggregates in the center of muscle fibers

Dermatomyositis (DM-VP): MxA staining

DM-VP
  MxA strongly stains
    Perifascicular muscle fibers
    Endomysial capillaries

MxA stain
Control Muscle
  No MxA staining of: Muscle fibers or Endomysial capillaries

MxA stain

Dermatomyositis (DM-VP): Inflammation

DM-VP: Mononuclear cell focus
  Location: Separate from atrophic perifascicular muscle fibers

VvG stain

H&E stain
Mononuclear cell inflammation: Foci
  Cell types: Lymphocytes + Scattered histiocytes
  Location: Perimysium
  Also Contain: Intermediate-sized vessels

Congo Red stain
Lymphocyte foci contain: Intermediate sized vessels

VvG stain
Cell foci: Contain scattered histiocytes (Acid phosphatase +)

Acid phosphatase stain
Vessels in cell foci (Arrow): Endothelial cells often stain for esterase

Esterase stain
Mononuclear cell inflammation: Foci
  Cell types: Lymphocytes + Scattered histiocytes
  Location
    Perimysium
    Distant from muscle fiber atrophy
  Contain: Intermediate-sized vessels

 
H&E stain
H&E stain
Mononuclear cell inflammation:
Stains for CD4 and, in some regions, CD20 (B-cells)
Commonly perivascular.

CD4 stain
CD20 stain
Congo red stain

Childhood dermatomyositis (DM-VP): Capillary pathology

Capillaries: Ulex staining of Endothelium


Stain: Ulex europaeus agglutinin I

Dermatomyositis: Capillaries
  Capillary pathology is patchy and most prominent in perifascicular regions.
  Capillary staining with Ulex lectin is often absent in regions with small perifascicular muscle fibers (Above left).
  Capillaries in regions near perifascicular atrophy are often enlarged (Above right).

Stain: Ulex europaeus agglutinin I

Stain: Ulex europaeus agglutinin I

Control: Capillaries are abundant and small
CAPILLARY PATHOLOGY: Regional

Stain: Ulex europaeus agglutinin I (UEAI)
Muscle fiber atrophy (Top)
  Few stained capillaries
  Many muscle fibers with no adjacent capillary.
Region neighboring muscle fiber atrophy (Purlieu; Middle & Below)
  Enlarged capillaries
  Increased staining for alkaline phosphatase; Also see
Region distant from muscle fiber atrophy: Capillaries have nearly normal size and number
Endomysial capillaries in region neighboring muscle fiber atrophy (Purlieu):
  Abnormal staining for alkaline phosphatase: Also see

Alkaline phosphatase stain
Alkaline Phosphatase

Enlarged capillaries (Arrows): In regions neighboring the smallest muscle fibers: Also see
  Fewer capillaries stain among larger fibers or amid the smallest fibers at the edge of fascicles.

Alkaline phosphatase stain
Endomysial Capillaries

Alkaline phosphatase Staining: Especially in perifascicular regions

Alkaline phosphatase stain
Alkaline phosphatase stain

Capillaries: PECAM-1 & Collagen IV stains

Normal capillaries
Dermatomyositis
  Enlarged capillaries
  Capillary remnants

NORMAL ENDOMYSIAL CAPILLARIES

Ultrastructure
Endothelium + Collagen IV
  Collagen IV: Stains Capillary walls (Red & Yellow) & Basal lamina around muscle fibers (Red).
  PECAM1: Stains Capillary endothelium in lumens (Green) and overlaps Collagen IV (Yellow) in walls.


Capillary amidst Normal muscle fibers: Normal size & morphology.
  Capillary compositon
    Endothelial cells (E): Next to lumen
    Basal lamina: Thick; Surrounds endothelial cellls
    Pericyte (processes) (P).
    Red blood cell: In capillary lumen


Dermatomyositis (DM-VP): SMALL ENDOMYSIAL CAPILLARY REMNANTS in areas of Perifascicular Atrophy

Ultrastructure
Endothelium + Collagen IV
Collagen IV (Red) stains small capillary wall remnants (Arrow) without lumens.
PECAM1 stains little, or no, capillary endothelium.



Pericytes & Cells + Collagen IV
Collagen IV (Red & Yellow) stains round capillary remnants and basal lamina around muscle fibers.
PDGFRβ stains capillary pericytes (Yellow) overlapping Collagen IV & elongated endomysial cells (Green).


Dermatomyositis (DM-VP): Capillary Ultrastructure
Capillaries
  Normal
  Atrophic
  Enlarged
  Tubuloreticular profiles
Capillary in area of Perifascicular atrophy: Small endomysial capillary residua (Arrow)
  Basal lamina
    Thick
    Differs from thin basal laminae of nearby muscle fibers (Arrowhead)
  Lumen: No endothelium within basal lamina
  Neighboring Pericyte: Provides evidence of the pathologic vessel's microvascular origin)


Dermatomyositis (DM-VP): ENLARGED ENDOMYSIAL CAPILLARIES
  Ultrastructure
  Location: Near regions of Perifascicular Atrophy

Endothelium + Collagen IV stains
  Collagen IV: Capillary walls (Red & Yellow) & Basal lamina around muscle fibers (Red).
  PECAM1: Capillary endothelium in lumens (Green) & Some overlaping Collagen IV (Yellow) in walls.

Enlarged endomysial capillaries (Arrows)
Location: Neighbor regions of perifascicular muscle fiber pathology .
 
H&E stain
Capillaries in Intermediate zones
  Size: Enlarged
  Endothelial cells
    Size: Enlarged & Abundant cytoplasm
    Tubular reticular profiles (Dark arrows): Present in cytoplasm
    Abnormal mitochondria (White arrow): Present in some cells
  Capillary components
Tubular Reticular Structures (Undulating tubules)
  Location: Cytoplasm of capillary endothelial cells
  Continuous with: Endoplasmic reticulum
Enlarged capillary: In intermediate zone
  Endothelial cells have
    Abundant cytoplasm
    Tubular reticular structures (Arrow)
Tubular Reticular Structures
Endothelial cell cytoplasm: Contains Mitochondria & Weibel Palade bodies
Weibel Palade bodies
  Structure: Elongated, cigar-like shape (0.2 μm in width; Up to 4 μm in length)
  Location: Endothelial cells
  Function: Secretory organelles; May be exocytosed
  Contents: Proteins that contribute to inflammation, angiogenesis & tissue repair
    von Willebrand factor (VWF)
    Other
      tPA, P-selectin, Interleukin-8 (IL-8), Eotaxin-3, Angiopoietin-2
      Osteoprotegerin, Endothelin-1, Endothelin-converting enzyme, Calcitonin gene-related peptide

Childhood dermatomyositis (DM-VP): Complement (C5b-9) deposition on Endomysial capillaries



Stain: C5b-9 components of complement (Membrane attack complex)
Dermatomyositis: C5b-9 deposition in endomysial capillaries
Changes are patchy and most prominent in perifascicular regions amid small muscle fibers.
C5b-9 is deposited on damaged endomysial capillaries that have often lost their endothelium.
Stain: C5b-9 components of complement (Membrane attack complex)
Normal control
No C5b-9 deposition in endomysial capillaries in control muscle

C5b-9 stain
C5b9 complement compared to PECAM1 staining of Punctate Capillary Remnants
Endomysial capillaries: C5b-9 complement deposits

C5b-9 complement (Green) with Collagen IV (Red)
 Endomysial capillaries: No endothelium

PECAM1 (Green) with Collagen IV (Red)

Childhood dermatomyositis (DM-VP): Perimysial Vascular Pathology

Vessel walls: Abnormal structure
Damaged vessels: Fragments without lumens

Perimysial Arteries (a) & Veins (v)

VvG stain
  Normal vessels (Above, Left)
  DM-VP (Above Right & Below)
    Loss or thinning of fibrils in walls of arteries & veins
    Endothelial cells: Enlarged, May contain tubulo-reticular profiles

VvG stain
Perimysial Vessels
  Fibrils in wall reduced

VvG stain
Vessel, Moderate-sized
  Endothelial cells large
  Wall: No fibrils
Perimysial vascular fragments: No lumen

VvG stain
Dermatomyositis (DM-VP): Vascular Perimysium
  Contains abnormal vascular fragments (Yellow)
  Has increased PECAM1 staining
  Located away from perifascicular muscle fiber atrophy
  PECAM1 (Green) + Collagen IV (Red): Overlap = Yellow
Normal: Vascular Perimysium
  Contains normal intermediate-sized vessels with lumens
  Has minimal PECAM1 staining
  PECAM1 (Green) + Collagen IV (Red): Overlap = Yellow

DM-VP (Childhood dermatomyositis): MHC Class I upregulation

Distribution
Pathology degree
  Severe
  Mild
DM-VP, Moderately severe: MHC-I up-regulation by muscle fibers, more in small fibers at edge of fascicle

MHC Class I
MHC Class I

Normal: MHC I not present in muscle fibers.
Staining is only on capillaries
 
MHC Class I up regulation at the edge of fascicles
  Perifascicular muscle fibers near avascular perimysium express MHC-I
  Central muscle fibers near vessel (Arrow; Below) express less, or no, MHC-I

MHC Class I
DM-VP, Mild: Patterns of MHC-I staining
  MHC-I up-regulation more in muscle fibers at edge of fascicle, or diffusely
  Affected muscle fibers may be normal size, or small.
MHC Class I upregulation
  Mild
  More in muscle fibers in perifascicular region
  May occur in regions without myofiber atrophy
 DM-VP: MHC I up on muscle fibers
  especially near perimysium
A similar pattern may occur in IMPP syndromes



Stain: MHC Class I

MHC Class I stain
MHC Class I upregulation
  Dffuse
  Slightly more prominent in perifascicular region
  May occur in regions without severe myofiber atrophy
DM-VP: MHC I up on muscle fibers, severe
  Diffusely on the surface and within muscle fibers


Stain: MHC Class I

Dermatomyositis with Vascular Pathology (DM-VP): Severe


H&E stain
Center of Fascicle: Artery-Vein pair
Periphery of Fascicle: Atrophic muscle fibers near avascular perimysium

VvG stain
Small Muscle Fibers

Gomori trichrome stain
Purlieu Zone: Between areas with larger & very small muscle fibers
  Muscle fibers: Intermediate-sized
  Endomysial capillaries: Large

Gomori trichrome stain
Very Small Muscle fibers
  Near perimysium
  Nuclei: Often internal
  Surface: Irregular
  Cytoplasm: Dark NADH stain

NADH stain

VvG stain

VvG stain
Intermediate-sized Perimysial Vessels
  Abnormal structure: Loss of fibrils in arteries & veins
  Also see: DM-VP Vessels

VvG stain

DM-VP (Childhood): Muscle fiber Atrophy at Muscle Surface (Epimysium)

Severe atrophy of muscle fibers at edge of muscle

H&E stain

H&E stain
Muscle fibers in purlieu zone, near & beneath area of severe fiber atrophy
  Nuclei: Enlarged: Internal
  Muscle fibers: Intermediate size
  Endomysial capillaries: Large

H&E stain

Gomori trtichrome stain
Muscle Fibers: Perifascicular Atrophy

VvG stain

Congo Red stain
Internal Architecture
  Smallest muscle fibers: Very dark stained
  Intermediate-sized muscle fibers: Irregular staining & aggregates
  Endomysial capillaries: Positive staining

NADH stain

Cytochrome oxidase stain
Mitochondrial Pathology
  Muscle fibers in, & near, region of atrophy have reduced COX
  Muscle fibers in, & near, region of atrophy have inreased SDH, diffusely, or as aggregates

SDH stain
Muscle fibers in purlieu zone contain aggregated, cytoplasmic material

VvG stain
Endomysial Capillaries: Reduced staining in regions with small muscle fibers
  Some small mnuscle fibers have no adjacent capillary

VvG stain

DM-VP (Adult)


H&E stain
Muscle fibers: Perifascicular Atrophy
Lymphocyte focus: In perimysium

Congo Red stain

H&E stain
Lymphocyte Focus
  Location: Perimysium
  Contents: Lymphocytes & Small vessels

Congo Red stain
Vessels within Lymphocyte foci

Congo Red stain

H&E stain
Muscle Fibers
  Small at edge of fascicles
  Nuclei: Large; Often internal
  Internal architecture: Abnormal; Aggregates

VvG stain

H&E stain
Perifascicular Muscle Fibers
  Small
  Nuclei: Large; Often several internal

H&E stain

H&E stain
Perifascicular Muscle Fibers
  Small
  Nuclei: Large; Often several internal
  Internal architecture: Aggregates & Vacuoles

VvG stain

NADH stain
Muscle Fiber Internal Architecture
  Small Muscle fibers: Dark stained
  Larger Muscle Fibers: Sarcoplasmic reticulum aggregates

NADH stain
Myosin ATPase
  Small muscle fibers at edge of fascicles: Reduced staining

ATPase pH 9.4 stain
DM-VP: MHC Class I

MHC-I stain
MHC-I
  Small muscle fibers: MHC-I upregulation in cytoplasm & on surface
  Larger muscle fibers: MHC-I mostly on muscle fiober surfaces
DM-VP: Mitochondrial Pathology

COX stain
Mitochondrial stains: Small muscle fibers
  Cytochrome oxidase (COX): Reduced (Above)
  Succinate Dehydrogenase (SDH): Increased (Below)

SDH stain

Mitochondria: Proliferation & Abnormal shapes
DM-VP: Aggregates in Muscle Fibers

AMPDA stain
Aggregated material in muscle fiber cytoplasm stains for AMPDA & LC3

LC3 stain

LC3 stain
Autophagic debris in muscle fibers

Acid phosphatase stain
Acid phosphatase positive granules in muscle fiber cytoplasm
Large Artery
  Abnormal structure: Patchy loss of internal fibrils

VvG stain
Large Vein
  Abnormal; Endothelial layer is widened

VvG stain
Perimysial Smaller Vessel
  Thick wall

VvG stain
DM-VP: Capillaries

Alkaline phosphatase stain
Increased numbers of enlarged, alkaline phosphatase positive, endomysial capillaries in regions near muscle fiber atrophy

UEA I stain
UEA I positive endomysial capillaries: Reduced numbers in regions of perifascicular muscle fiber atrophy
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References
1. Neuromuscul Disord 2006;16:391-393
2. Muscle Nerve 2010; Online April

12/4/2024