Neuromuscular

MUSCLE FIBER ATROPHY & SMALLNESS

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

Atrophy, Severe & Diffuse


Muscle fiber atrophy

All muscle fibers are small

H&E stain

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

H&E stain


H&E stain
Small Muscle Fibers
  Shapes: Varied
  Surface: Irregular
  Nuclei: Large; Pale
  Sizes: Varied

H&E stain


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

Congo red stain


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

VvG stain

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

ATPase pH 9.4 stain

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

NADH stain

Muscle Fiber Atrophy
  Clustered lipofuscin granules

Acid phosphatase stain

See
  Fiber type disorders
  Fiber type properties

Muscle Fiber Atrophy: Diffuse, Early


H&E stain
Fiber Sizes
  Mildly small
  Bimodal distribution
Fiber Shapes
  Polygonal
  Surface membrane: Irregular

Gomori trichrome stain


VvG stain
Fiber Shapes
  Polygonal
  Surface membrane: Irregular
Internal Architecture
  Irregular

NADH stain


ATPase pH 9.4 stain
Fiber Types
  Type 2 fiber atrophy > Type 1

ATPase pH 4.3 stain

ATPase pH 4.6 stain

Neuromuscular Junctions
  Remain dark stained

Esterase stain

Atrophic Muscle fibers: Ultrastructure

Nuclear clumps
Small muscle fibers

Atrophic fibers: General Features

Atrophic Muscle Fibers
Undulating Basal lamina & Sarcolemma


From: Sean Ferris
Fiber size: Small
Sarcomere structure: Disorganized

From: Sean Ferris

From: Sean Ferris


From: Cory Toth MD
Pyknotic nuclear clump: Ultrastructure

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Return to Myopathies with wasting

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

2/8/2021