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MUSCLE FIBER TYPES

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Abnormal muscle with many scattered Immature muscle fibers

2C fibers Disorders MYH components   Control muscle   ALS Staining: Histochemistry

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Muscle Fiber Types

ATPase pH 4.3

ATPase pH 4.3 stain

• Type 1 fibers: Dark; Fibers contain MYH7
• Type 2 fibers (Usually): Very pale; Fibers contain MYH2 + other MYH types
• Type 2C fibers (Immature): Intermediate stained (Arrow); Fibers contain MYH7 > MYH2

ATPase pH 4.3 stain

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ATPase pH 4.6 stain

ATPase pH 4.6 stain

• Type 1 fibers: Dark
• Type 2A fibers: Pale
• Type 2B fibers: Intermediate
• Type 2C fibers (Immature): Intermediate; Darker than type 2B

ATPase pH 4.6 stain

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ATPase pH 9.4 stain

ATPase pH 9.4 stain

• Type 1 fibers: Intermediate
• Type 2 fibers: Dark
• Type 2C fibers (Immature): Intermediate; Darker than type 1

ATPase pH 9.4 stain

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Type 2C (Immature) muscle fibers

• Myosin heavy chain contents: Type 1; Type 2A
• May be associated with
  • Development & Young age
    • Excess 2C fibers with normal morphology: Coenzyme Q10 deficiency in infancy
  • Regeneration
  • Reversion of mature muscle fibers to immature state
  • CoQ10 deficiency in young children
• Morphology: Variable
  • Normal size & Internal architecture
  • Morphology
  • Small size: May occur with denervation & reinnervation
  • Muscle fibers with other histological features of immaturity: Regeneration after muscle fiber damage

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Type 2C muscle fibers: Increased numbers (Same muscle biopsy as above) with normal fiber morphology
  Fiber size: Mild variation
  No regenerating, or morphologically immature, muscle fibers

H&E stain

VvG stain

Internal architecture
  Unremarkable
  Rare internal nucleus

Gomori trichrome stain

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MYH stains = Green; Collagen IV = Red

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ALS Muscle: Fiber Types

Type 1 fibers: Normal
  ATPase: Intermediate color at pH 9.4 & Dark at pH 4.6 & 4.3
  All have MYH7, but not MYH2 or MYH1
Type 2 fibers: Variant
  All have MYH2 & moderate MYH7
Type 2A fibers
  All have MYH2 & Moderate MYH7, but no MYH1
  ATPase: Dark at pH 9.4; Pale at pH 4.6 & 4.3
Type 2B fibers
  All have MYH2 & Moderate MYH7 & MYH1
  ATPase: Dark at pH 9.4; Intermediate at 4.6; Pale at pH 4.3
Type 2C fibers
  All have MYH2 & MYH7, but no MYH1
  ATPase: Moderately Dark at pH 9.4 & 4.6; Internediate at pH 4.3

MYH stains = Green; Collagen IV = Red

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MYH stains = Green; Collagen IV = Red

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MYH stains = Green; Collagen IV = Red

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11/15/2021