---

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 Muscle Fibers: General Features

• Size: Small
• Internal architecture
  • Myofibril & Sarcomere disorganization
  • Z-band streaming
• Muscle fiber surface
  • Basal lamina: May project empty sleeves or redundant loops from fiber surface
  • May be smooth or undulating

---

Atrophic Muscle Fibers
Undulating Basal lamina & Sarcolemma

---

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

From: Sean Ferris

---

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

From: Sean Ferris

---

From: Sean Ferris

Fiber size: Small
Sarcomere structure: Absent or Disorganized

---

Atrophic Muscle fiber   Z-Band streaming, Rod-like (Arrow)

---

From: Cory Toth MD Pyknotic nuclear clump: Ultrastructure

---

Return to Neuromuscular Home Page
Return to Myopathies with wasting

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

7/22/2023