Neuromuscular

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

DM-VP
Muscle fiber pathology
  Aggregates
  Vacuoles
  MHC Class I
  Perifascicular atrophy: Stains
    Gomori trichrome
    H&E
    NADH
    Mitochondrial
    Alkaline phosphatase
    Toluidine blue
Vessel pathology
  Capillaries, Endomysial
    H&E stain
    Alkaline phosphatase
    Complement deposition
    Endothelial stains
      Ulex
      Immunohistochemistry
    Ultrastructure
  Intermediate-sized, Perimysial
    Damage
    Inflammation

Severe disease

Other DM
  IMPP
  RIIM

Br J Child Dis 1912;9:247


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


Original Pathologic Description of Dermatomysitis with Vascular Pathology

Batten FE Br J Child Dis 1912;9:247
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
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 are small & stain darkly
Muscle fibers near vascular perimysium are more normal (Below, Arrow)


NADH 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 more obvious on ATPase stains.
Small fibers are both types I & II.

ATPase pH 4.3

ATPase pH 4.3 stain

Type IIC muscle fibers (intermediate staining) are present in regions of atrophy and larger muscle fibers.
Few, or no, type 1 muscle fibers in regions of most severe atrophy at edge of fascicles (Below; Arrow).


ATPase pH 4.3 stain

Type IIC muscle fibers are large & small
Small muscle fibers are near avascular perimysium.
Fibers near intermediate-sized perimysial vessel are larger.

PAS

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

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

Alkaline phosphatase may stain several different structures in patients with dermatomyositis.

Alkaline phosphatase stain

Alkaline phosphatase stain

Alkaline phosphatase stain
Perimysium
Vascular staining.
More common in children
Endomysium
Capillary staining, especially
in perifascicular regions.
Perimysium
Diffuse staining.
More common in adults
Rare in children


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

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

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): Inflammation


Vvg stain
Mononuclear cell inflammation: Foci:
  Cell type: Lymphocytic
  Location
    Perimysium
    Around intermediate-sized vessels
    Distant from muscle fiber atrophy


 
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 or 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
Muscle fiber atrophy (Top): Few stained capillaries
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

Stain: Ulex europaeus agglutinin I (UEAI)

Endomysial capillaries in region neighboring muscle fiber atrophy (Purlieu):
  Abnormal staining for alkaline phosphatase: Also see

Alkaline phosphatase stain

Capillaries: PECAM-1 & Collagen IV stains

Normal capillaries
Dermatomyositis
  Enlarged capillaries
  Capillary remnants


NORMAL ENDOMYSIAL CAPILLARIES

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.


Dermatomyositis (DM-VP): ENLARGED ENDOMYSIAL CAPILLARIES
  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

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


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) Capillaries in area of perifascicular atrophy: Ultrastructure
Small endomysial capillary residua (Arrow)
  Basal lamina: Thick
    Differs from thin basal laminae of nearby muscle fibers (Arrowhead))
  No endothelium within basal lamina
  Neighboring Pericyte cytoplasm: Provides evidence of the pathologic vessel's microvascular origin)



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



Childhood dermatomyositis (DM-VP): Complement (C5b-9) deposition in 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 (Left)
  DM-VP (Right & Below)
    Loss or thinning of fibrils in walls of arteries & veins
    Endothelial cells: Enlarged

VvG stain

VvG stain

Perimysial vascular fragments with 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

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 ner avascular perimysium express MHC-I
  Central musclle 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

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References
1. Neuromuscul Disord 2006;16:391-393
2. Muscle Nerve 2010; Online April

10/6/2016