Abnormal muscle with many scattered Immature muscle fibers

Muscle Fiber Types

ATPase pH 4.3

• 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

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

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

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

H&E stain

VvG stain

Gomori trichrome stain

ALS Muscle: Fiber Types

MYH stains = Green; Collagen IV = Red

MYH stains = Green; Collagen IV = Red

MYH stains = Green; Collagen IV = Red