Neuromuscular

Small Vessel Pathology (Capillaries or Endoneurial Microvessels) 2

Capillaries
  Muscle
    Normal
    Staining Analysis
    Ultrastructure
    Disorders
    Features
      C5b-9 Deposits
      Enlargement
        Differential diagnosis
        Pipestem
        SRP Myopathy
        Thick vessel walls
        TS-HDS neuropathy
      Loss or Damage
        DM-VP
        GvHD
        Systemic Sclerosis
          Minimal myopathy
            Ultrastructure
          Myopathy + Capillary Δ
  ELS vessels
Nerve
  Endoneurial Microvessels
  Microvasculopathy
    C5b-9 Deposits
    HIEM (Nerve)
  Hemosiderin
  Endoneurial inflammation
    Ipilimumab
    Perineuritis
  Subperineurial edema
Endomysial Capillary: Normal

ENDOMYSIAL CAPILLARIES

Capillary
  Endothelial cell = E: Lumenal side of vessel wall
  Pericyte = P: Several within basal lamina, outside of endothelial cell processes
  Basal lamina: 1 to 3 Thin layers around outside of capillary

Capillary Structure

Basement membrane
  Around & outside endothelial cell layer
  May be homogeneous or layered
  Contains pericytes (P)
  Composition
    Collagen IV
    Laminin
    Glycoproteins: Fibronectin, Nidogen-1, Nidogen-2 (Entactin)
    Proteoglycans (as HSPG): Perlecan, Agrin
  Thickening: Differential diagnosis
Fibroblasts
  Not present
Endothelial cells (E)
  Surround lumen
  Stains: Ulex Europaeus Agglutinin I (UEAI); CD31
  Other markers: ADGRF5, BTNL9, VWF
Pericytes (P)
  Location: Within basal lamina of vessel wall
  Contractile
  Frequency vs Endothelial cells: 1:10 to 1:100
  Markers: PDGRFβ; NG2, Desmin, KCNJ8; ABCC9; CD13
Smooth muscle
  Markers: Smooth muscle actin; PDGRFβ; CD13; NG2; CD146; Desmin
Histiocytes
  Markers: CD163; CD206; LYVE1; F4/80; HAM56

Muscle Capillaries: Features

Anatomy Plasticity
Endomysial Capillary Features: Stain & Molecular Analysis
Endothelial
Cells
Basement
Membrane
Immune
H&E: Morphology
Ulex: Distribution;
  #; Size; Stain intensity
ATPase pH 4.3: #+
Alkaline phosphatase: #+
NADH: + or -
Other markers: VWF,
  BTNL9, ADGRF5
Morphology
  H&E
  GT/VvG
  Ultrastructure
Molecular
  Decorin/Col IV
  PAS: + or -
Pericytes
  PDGFRβ
Humoral
  C5b-9
Cellular
  Acid phosphatase
  HAM56
Cell involvement
  Muscle: MHC I
  Capillary: MxA

Endomysial Capillaries: Normal


UEA I stain
Endomysial capillaries: Normal
  Normal number: Every muscle fiber has at least one adjacent capillary
  Orientation: Run parallel to muscle fiber length; Cut in cross-section

UEA I stain
All muscle fibers have at least one adjacent capillary

UEA I stain

There are few or no capillaries immediately adjacent to the perimysium

UEA I stain

Endomysial Capillaries: Reduced numbers

Some muscle fibers have no adjacent capillary

UEA I stain

Endomysial Capillaries: Partial Denervation


UEA I stain
Endomysial capillaries
  Orientation: Abnormal; May be circumferential around muscle fibers (Above) cut in cross-section
  Number: Increased; Every muscle fiber has several adjacent capillaries

UEA I stain

Endomysial Capillaries: Dermatomyositis with Vascular pathology (DM-VP)

Endomysial capillaries
  Orientation: Normal
  Number: Reduced or absent Endothelium (Ulex stain) in regions with small muscle fibers (Arrow)
    Endothelium is lost but basal lamina is still present
      & may have C5b-9 deposition
  Size: Increased in regions neighboring muscle fiber atrophy

UEA I stain

Endomysial Capillaries: Enlarged


UEA I stain

UEA I stain
Patient history: Cardiac failure & Interstitial lung disease

Muscle: Endomysial Capillary Vasculopathy

Muscle: C5b-9 Deposits
  On Endomysial capillaries
Microvasculopathy
Control Muscle
Microvasculopathy: C5b-9 Deposits on many endomysial capillaries

Muscle (Endomysial) Capillaries: Ultrastructure

Dermatomyositis (DM-VP)
  Damaged
  Large
  Tubuloreticular profiles
Normal: A; B
Thick Walls
  Homogenous
  Multilayered
  TS-HDS antibodies
Systemic sclerosis

Endomysial Capillary: Normal
  Lumen: Patent
  Endothelial cell processes: Form inner layers of capillary wall
  Pericyte (White arrow): Around endothelial cell processes
  Basal lamina: Thin

Endomysial Capillary: Normal
  Lumen: Patent; Contains erythrocyte
  Endothelial cell processes: Form inner layer of capillary wall
  Pericyte: Not visible
  Basal lamina (White arrow): Thin
  Nucleus (Large; Upper right): Probably a muscle fiber nucleus

Endomysial Capillary: Normal
  Lumen: Patent
  Endothelial cell processes: Form inner layer of capillary wall
  Pericyte: Not visible
  Basal lamina (White arrow): Thin
  Nucleus (Large): Neighbors capillary; May be a resident histiocyte

Endomysial Capillary: Basal lamina thick & homogeneous
  Lumen: Patent
  Endothelial cell processes: Form inner layer of capillary wall; Vesicles in cytoplasm
  Basal lamina: Thick, Homogeneous; Contains a few small cell processes

Endomysial Capillary: Basal lamina thick & homogeneous
  Lumen: Patent
  Endothelial cell processes: Form inner layer of capillary wall; Vesicles in cytoplasm
  Basal lamina: Thick, Homogeneous; Contains a few small cell processes

Endomysial Capillary: Basal lamina thick & homogeneous
  Lumen: Patent
  Endothelial cell processes: Form inner layer of capillary wall; Vesicles in cytoplasm
  Basal lamina: Thick, Homogeneous; Contains a few small cell processes

Endomysial Capillary: Basal lamina thick & homogeneous
  Lumen: Patent
  Endothelial cell processes: Form inner layers of capillary wall
  Basal lamina
    Width: Thick
    Structure: Homogeneous
    Contains a few small cell processes
    Outer edge: Irregular

From Robert E Schmidt

Endomysial Capillary in Muscle
  Lumen: Contains erythrocyte
  Endothelial cell: contains large nucleus
  Basal lamina: Mildly thick: Outer edge irregular

Endomysial Capillaries: Thick walls with Multilayered structure
  Lumen: Patent; May contain erythrocyte (Above)
  Endothelial cell processes: Thick; Form inner layers of capillary wall
  Pericyte processes: Present within basal lamina layers
  Basal lamina
    Width: Thick
    Structure: Multilayered; Varied around vessel circumference
    Contains pericyte processes
    Outer edge: Irregular
  Fibrocyte processes (Arrows): Neighbor outer edge of capillary

Also see: Systemic sclerosis, Endomysial capillaries

NERVE: Endoneurial Microvessels



H&E stain
Endoneurial Microvessel (Arrow)
  Orientation: Along length of nerve

Endoneurial Microvessel Walls
  Endothelial cells: Toward lumen
  Pericytes (Arrows): Within, or outside, microvessel wall (Basal lamina)

Toluidine blue stain

Endoneurial Microvessels: Near Normal
Endoneurial Microvessels
  Lumen: Filled with RBCs
  Endothelial cell with nucleus (Black arrow)
    Neighbored around lumen by Endothelial cell processes
  Pericyte (Gray arrow)

Endoneurial Microvessel: Surrounded by Pericyte processes
Endoneurial Microvessel
  Lumen: Filled with RBC
  Endothelial cell with nucleus
    Neighbored around lumen by other Endothelial cell processes
  Pericytes
    Surround microvessel
  Basal lamina: Surrounds microvessel & pericytes
Endoneurial Microvessel: Surrounded by Pericyte processes
Endoneurial Microvessel
  Lumen: Contains 1 RBC
  Endothelial cells: 2 nuclei are present
    Neighbored around lumen by other Endothelial cell processes
  Pericyte processes
    Surround microvessel

Endoneurial Microvessels: "Closed"; Lumen is filled by endothelial cell processes
Endoneurial Microvessel, "Closed"
  Lumen: None; Region is filled by endothelial cell processes
  Endothelial cells: 1 nucleus is present
    Neighbored in lumen by Endothelial cell processes
  Pericyte processes: Surround endothelial cell processes
  Basal lamina: Few thin layers of connective tissue incompletely surround vessel
  Also see: HIEM

Endoneurial Microvessel, "Closed"
  Lumen: None; Region is filled by endothelial cell processes
  Endothelial cells: 1 nucleus is present
  Pericyte processes: Surround endothelial cell processes
  Basal lamina: Increased layers of connective tissue surround vessel

Endoneurial Microvessel, "Closed"; Surrounding cells
  Lumen: None; Region is filled by endothelial cell processes
  Endothelial cells: 2 nuclei are present
  Pericyte processes: Surround endothelial cell processes
  Basal lamina: Few thin layers of connective tissue incompletely surround vessel
  Surounding cells: Increased cellularity aroound endoneurial microvessel

Endoneurial Microvessel Endothelium: Increased numbers & processes of endothelial cells
  Lumen: Present
  Endothelial cells & processes: Multiple
  Pericyte processes: Surround endothelial cells
  Basal lamina: Layers of connective tissue around vessel moderately increased
  Disease: HIEM

Endomysial & Endoneurial Capillaries: Thick Walls


Capillary Walls Thick: Differential diagnosis 1

Endoneurial Microvessel: Thick Basal Lamina
  Lumen: Present
  Endothelial cells & processes: Present
  Pericyte processes: Surround endothelial cell layer
  Basal lamina: Increased connective tissue layers
Patient Clinical: No diabetes, Motor-sensory axonal PN

Endoneurial Microvessel: Thick Basal Lamina
  Lumen: Present
  Endothelial cells & processes: Present
  Pericyte processes: Surround endothelial cell layer
  Basal lamina: Increased connective tissue layers
Patient Clinical: No diabetes, Motor-sensory axonal PN


From: Chunyu Cai
Endoneurial microvessel (Diabetes)
  Basal lamina: Thick; Multilayered (Arrow)
  Endothelial cell: Dark-stained cytoplasm


Ultrastructure: From Robert E Schmidt
Diabetes
Endoneurial Microvessel
  Basal lamina:
    Thick
    Contains: Multiple thin layers

Endoneurial Microvessel: Basal Lamina Fragmentation (HIEM)

Endoneurial Microvessel
    Basal lamina: Rarified & Wide, especially outer layers

  Lumen: Present
  Endothelial cells & processes: Present
  Pericyte processes: Not prominent
  Basal lamina (Arrow)
    Layers of connective tissue around vessel: Moderately increased
    Outer layers of connective tissue: Pale & Disorganized

Endoneurial Microvessel: Basal Lamina Disorganized (HIEM)

Endoneurial Microvessel
    Basal lamina: Rarified & Wide, especially outer layers

  Lumen: Present
  Endothelial cells & processes: Present
  Pericyte processes: Not prominent
  Basal lamina (Arrow)
    Layers of connective tissue around vessel: Moderately increased
    Outer layers of connective tissue: Pale & Disorganized

Endoneurial microvessels
  Basal lamina: Thick; Homogeneous (Arrows)
Endoneurial microvessel
  Basal lamina: Normal (Arrow)

Endoneurial Microvessels: Walls have varied thickness

Humoral Immune Endoneurial Microvasculopathy (HIEM) 28

Microvessels
  C5b-9 deposition on Microvessels
  C5b-9 around Endothelial cells
  Endoneurial Microvascular Endothelial cells: Large
Nerve
  Histology
  Axon loss
    Varied: Toluidine blue
    Large > Small

Associated Clinical Syndrome

C5b-9 stain
HIEM Nerve
C5b-9 Stains Most Endoneurial Microvessels
Disease Control Nerve
C5b-9 Stains Perineurium & Epineurial vessels but not Endoneurial microvessels

C5b-9 stain

HIEM Nerve
C5b-9 Stains Endoneurial Microvessels

C5b-9 stain


C5b-9 stain

Endoneurial Microvasculopathy
  HIEM: C5b-9 stains Endoneurial microvessels

C5b-9 stain
Disease Control Nerve
  C5b-9 does not stain Endoneurial microvessels

C5b-9 stain


C5b-9 (Green) + UEAI (Red) stain
HIEM: C5b-9 stain (Green) around Endoneurial Microvessel endothelium (Red)

C5b-9 (Green) + UEAI (Red) stain

C5b-9 (Green) + UEAI (Red) stain


Toluidine blue stain
Endoneurial Microvessel Pathology
  Vessel size: Normal or Large
  Vessel wall: Thick
  Endothelial cells: Large
  Basal lamina: Multi-layered; Fragmented
See: Ultrastructure

Toluidine blue stain

HIEM: Endoneurial Microvessel Ultrastructural Pathology

Basal lamina
  Fragmented: Common
  Disorganized
  Also see: Microvessel pathology
Closed lumens
Endothelial processes increased

Endoneurial Microvessel
    Basal lamina: Fragmented, Rarified & Wide, especially outer layers

  Lumen: Present
  Endothelial cells & processes: Present
  Pericyte processes: Not prominent
  Basal lamina (Arrow)
    Layers of connective tissue around vessel: Moderately increased
    Outer layers of connective tissue: Pale & Disorganized
Endoneurial Microvessel
    Basal lamina: Fragmented, Rarified & Wide, especially outer layers

  Lumen: Present
  Endothelial cells & processes: Present
  Pericyte processes: Not prominent
  Basal lamina (Arrow)
    Layers of connective tissue around vessel: Moderately increased
    Outer layers of connective tissue: Pale & Disorganized

Endoneurial Microvessel
    Basal lamina: Rarified & Wide, especially outer layers

  Lumen: Absent; Filled by endothelial cell processes
  Endothelial cells & processes: Present
  Pericyte processes: Not prominent
  Basal lamina (Arrow)
    Layers of connective tissue around vessel: Moderately increased
    Outer layers of connective tissue: Pale & Disorganized

From R Schmidt
HIEM Microvessel
  Endothelial cells: Multiple, Large
  Pericyte: Processes surround microvessel
  Basal lamina: Disorganized around outside of vessel


From R Schmidt
HIEM Microvessel
  "Closed": No lumen
  Endothelial cells: Multiple, Large
  Pericyte (Arrow): Process partially surrounds microvessel
  Basal lamina: Connective tissue layers surround most of the vessel

HIEM: Nerve anatomic pathology

H&E stain
HIEM nerve: No lymphocytic inflammation


VvG stain
HIEM: Differential fascicular involvement
  Myelinated axon loss: Varied (Above)
  Endoneurial ATPase stain: Varied (Below)

ATPase pH 4.3 stain


Toluidine blue stain
HIEM sural nerve
  Moderate loss of large & small myelinated axons
  Regeneration: Clusters of small myelinated axons
  Endoneurial microvessels
    Basal lamina: Thick
    Endothelial cells: Large

Toluidine blue stain


Toluidine blue stain
HIEM sural nerve
  Large & small myelinated axons: Severe loss (Above)
  Small unmyelinated axons: Relatively preserved (Below)

Neurofilament stain

Control sural nerve
  Large & Small axons are present

Neurofilament stain

Go to Moderate & large vessel vasculitis
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Return to Vasculitis

References
1. Acta Neuropathol 2000;100:445-450
2. Am J Physiol Heart Circ Physiol 2016 Jul 1
3. J Peripher Nerv Syst 2019;24:195-206

7/25/2024