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MUSCLE FIBER ATROPHY & SMALLNESS

Early Type 1 fibers Type 2 fibers Severe Nuclear clumps Denervation Ultrastructure Dermatomyositis

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Atrophy, Severe & Diffuse

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Muscle fiber atrophy

All muscle fibers are small

H&E stain

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Small Muscle Fibers
  Shapes: Varied
  Surface: Irregular
  Nuclei: Large; Pale

H&E stain

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H&E stain

Small Muscle Fibers
  Shapes: Varied
  Surface: Irregular
  Nuclei: Large; Pale
  Sizes: Varied

H&E stain

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Congo red stain

Small Muscle Fibers
  Shapes: Varied
  Surface: Irregular
  Nuclei: Large; Pale
  Sizes: Varied

Congo red stain

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VvG stain

Small Muscle Fibers
  Shapes: Varied
  Surface: Irregular
  Nuclei: Large; Pale
  Sizes: Varied
  Internal architecture: Variable; Coarse

VvG stain

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Muscle Fiber Atrophy
  All fibers very small
  Smallest muscle fibers: Type 2 (Dark)

ATPase pH 9.4 stain

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Muscle Fiber Atrophy
  Internal architecture: Moderately coarse
  Smallest muscle fibers: Intermediate stained

NADH stain

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Muscle Fiber Atrophy
  Clustered lipofuscin granules

Acid phosphatase stain

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See
  Fiber type disorders
  Fiber type properties

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Muscle Fiber Atrophy: Diffuse, Early

H&E stain

Fiber Sizes
  Mildly small
  Bimodal distribution
Fiber Shapes
  Polygonal
  Surface membrane: Irregular

Gomori trichrome stain

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VvG stain

Fiber Shapes
  Polygonal
  Surface membrane: Irregular
Internal Architecture
  Irregular

NADH stain

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ATPase pH 9.4 stain

Fiber Types
  Type 2 fiber atrophy > Type 1

ATPase pH 4.3 stain

ATPase pH 4.6 stain

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Neuromuscular Junctions
  Remain dark stained

Esterase stain

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Atrophic Muscle fibers: Ultrastructure

Nuclear clumps Small muscle fibers

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Atrophic Muscle Fibers: General Features

• Size: Small
• Internal architecture
  • Myofibril & Sarcomeres
    • Disorganization
    • Z-bands: Fragmentation; Streaming
    • Loss
• Muscle fiber surface
  • Basal lamina: May project empty sleeves or redundant loops from fiber surface
  • May be smooth or undulating

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Muscle Fiber Atrophy: Sarcolemma

Atrophic Muscle Fibers
Undulating Basal lamina & Sarcolemma

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Muscle Fiber Atrophy: Sarcomere Structure

Sarcomere structure (Right): Disorganized

From: Sean Ferris

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Sarcomere structure (Left): Disorganized
Lipid Droplet (Right; Arrow)

From: Sean Ferris

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Atrophic Muscle fiber   Z-Band streaming (Arrow)

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Muscle Fiber Atrophy: Severe

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From: Sean Ferris

Fiber size: Small
Sarcomere structure: Absent or Disorganized

From: R Schmidt

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From: R Schmidt

Sarcomere structure: Absent or Disorganized
Z-bands
  Fragmented
  Fragments similar to Cytoplasmic bodies or Rods

From: R Schmidt

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From: R Schmidt

Z-bands
  Fragmented
  Fragments similar to Cytoplasmic bodies or Rods

From: R Schmidt

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From: R Schmidt

Sarcomere structure: Absent or Disorganized

From: R Schmidt

From: R Schmidt

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Pyknotic nuclear clump: Ultrastructure

From: Cory Toth MD

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Return to Neuromuscular Home Page
Return to Myopathies with wasting

References
1. Am J Physiol Cell Physiol 2012; Online August

7/9/2024