Neuromuscular

TYPE II MUSCLE FIBER ATROPHY

Clinical features
Congenital
Disuse
Early
Pathological features

Disuse: Type II muscle fiber atrophy


Myosin ATPase, pH 9.4

Type 2 Atrophy: Early


Myosin ATPase, pH 4.6
Type IIB atrophy

Myosin ATPase, pH 9.4
Narrow, elongated muscle fiber

Congenital type II atrophy


Myosin ATPase, pH 9.4

Clinical features

Pathology

  • Type II (dark at pH 9.4) muscle fibers are small
    • Early changes
      • Atrophy in type IIB (Intermediate staining at pH 4.6) fibers
      • Narrow elongated muscle fibers
    • Disuse & weight loss atrophy: Small fibers are angular
    • Congenital: Small fibers are polygonal or rounded
  • Type I (lighter at pH 9.4) muscle fibers are larger than type II

See fiber type disorders
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8/13/2000