Normal: Checkerboard mix of type 1 & 2 fibers.

• Type 1: "1 slow fat red ox":
  • slow twitch
  • lipid accumulation
  • red fibers
  • oxidative
• Type 2: "2 fast skinny white breasts":
  • fast twitch
  • low lipid
  • white fibers

Atrophy – neuronal, ischemic, inflammatory.

Myositis: Inflammation, Muscular Dystrophy: embryonic disorganization.

Myopathy: non inflammatory abnormality. Toxic / Cong. (alcohol, drugs)

Tumours: Rhabdomyoma, Rhabdomyosarcoma.

Muscular Dystrophy

• Inherited, defective muscle structure.
• Mutation of Dystrophin on Xp21.
• Hypertrophy / Atrophy, degeneration → fat & fibrosis (pseudohypertrophy)
• Big muscles but need to climb on themselves to get up
• Common X linked 2 types:
  • Duchenne MD – common, early 5y, severe, death by 20y.
  • Becker MD -rare, adult, less severe.
• SMD: Normal at birth, starts with pelvic & limb weakness →heart failure.