Neuromuscular

Muscle: Chronic Partial Denervation

Muscle
  Capillaries
  Fibers
    Atrophy
      Ultrastructure
    Grouped atrophy
    Nuclei
      Internal
      Pyknotic clumps
    Necrosis
      Regeneration, Clustered
    Split
    Types
      Grouped
      Patterns
  Chronic Features
    Moderate
    Severe: Pseudomyopathic
    Endstage
Nerve
  Regenerating axon clusters

Groups (Size): Hypertrophic & Atrophic Muscle fibers



H & E stain
Large Muscle Fibers
  Distribution: Clustered
  Size: Often hypertrophied
Small Muscle Fibers
  Shape: Polygonal, Rounded or Nuclear Clumps
Endomysial connective tissue in regions of grouped muscle fiber atrophy
  Distribution: Clustered or Grouped
  Normal (Above) or Increased (Below)

H & E stain

Clusters, or groups, of large, intermediate & small sized muscle fibers

H & E stain
Grouped atrophy: Increased space between tiny muscle fibers

Gomori trichrome stain


VvG stain
Internal architecture: Hypertrophic muscle fibers have Irregular clear centers or Targets

NADH stain

Chronic Partial Denervation: Fiber type abnormalities
  Large fibers are commonly a single type: May be Type 1, 2, or Abnormal


ATPase pH 9.4 stain
Large muscle fibers: All type 1

ATPase pH 4.3 stain

Large muscle fibers: All type 2

ATPase pH 4.3 stain


ATPase pH 4.6 stain
Large, Type 2-like muscle fibers: Abnormal fiber types
  Type 2 with varied degrees of intermediate staining on ATPase pH 4.6 stain (Above)
  Incomplete fiber type switch: Type 1 properties on COX stain (Below)

COX stain

Atrophic Muscle fibers

H&E stain

H&E stain

Gomori trichrome stain

Congo Red stain

Esterase stain

NADH stain

PYKNOTIC NUCLEAR CLUMPS


Also see
Pyknotic nuclear clumps: Morphology

H & E stain

H & E stain

 

H&E stain


Congo red stain

Congo red stain
Pyknotic nuclear clumps: High magnification
  Clusters of myonuclei with no, Lipofuscin or little, visible cytoplasm
  May also contain clustered lipofuscin

H&E stain

Congo red stain


H&E stain
Pyknotic nuclear clumps: Grouped
  Late outcome of grouped muscle fiber atrophy

H&E stain

Congo red stain
Pyknotic nuclear clumps: Grouped
  Nuclear clusters: Some are associated with lipofuscin

Pyknotic nuclear clumps: Stain dark with esterase & NADH

NADH stain

Esterase stain
Angular fibers: Esterase
Esterase stain

Pyknotic nuclear clumps: With lipofuscin

Acid phosphatase stain

Acid phosphatase stain

Chronic Partial Denervation: Pseudo-Myopathic Changes



H& E stain
"Myopathic"-like changes

H& E stain

H&E stain

Gomori Trichrome stain

Gomori Trichrome stain

Large Muscle Fibers: Hypertrophy & Abnormal Internal Architecture


Split (Partially fused) Muscle Fibers (White arrows) 1

H&E stain

NADH stain

Internal Nuclei

H&E stain
Internal Nuclei
  Several myonuclei are scattered internally in cytoplasm of some muscle fibers
  Normal muscle fibers have all myonuclei in subsarcolemmal regions

H&E stain

H&E stain

Necrotic large muscle fibers → Clustered regeneration

Muscle Fiber Necrosis

H&E stain
  Large necrotic muscle fiber
    Invaded by many histiocytes
Clustered Regeneration (Arrows)

H&E stain

Clustered Regeneration

H&E stain
Hypertrophic muscle fibers: Undergo necrosis & are replaced by multiple smaller, partially-fused fibers
  Areas of grouped atrophy are also present in this image

NADH stain

Hypertrophic Muscle Fibers: Abnormal Internal Architecture

VvG stain

Gomori Trichrome stain

VvG stain

Gomori Trichrome stain

Chronic Denervation: Capillary Pathology


UEA I stain
Capillaries: Chronic Partial Denervation
  Abnormal orientation: Some become circumferential around muscle fibers
  Increased numbers of capillaries adjacent to each muscle fiber

UEA I stain

References
1. Skelet Muscle 2023;13:13

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8/14/2023