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Muscle biopsy: General features

• Variable fiber size: Small fibers rounded
• Hypercontracted (opaque) muscle fbers
• Myopathic grouping
• Muscle fiber degeneration & regeneration: Especially early
• Muscle fiber internal archetecture: Normal or immature
• Dystrophin: Absent staining
• Other membrane proteins
  • Sarcoglycans: Reduced
  • Aquaporin 4: Reduced
• Endomysial fibrosis: More with late pathology

Duchenne Muscular Dystrophy: Early Pathology

Necrotic muscle fibers: Grouped

Phagocytosis: Invasion of fibers by macrophages		Necrotic muscle fibers are pale on NADH stain

Myopathic grouping of regenerating muscle fibers

H & E stain	ATPase, pH 4.3
Acid phosphatase	NADH

H & E stain	ATPase, pH 4.3
Alkaline phosphatase	NADH

Staining properties of immature muscle fibers include:   1. H & E (left): Basophilic fibers   2. Alkaline phosphatase positive (center)   3. 2C fibers: Intermediate staining on ATPase pH 4.3 (right)

Duchenne Muscular Dystrophy: Later Pathology

­ Endomysial connective tissue increased Variable fiber size. Small fibers are rounded. Many hypercontracted muscle fibers

Normal dystrophin staining around the rim of muscle fibers.	Absent dystrophin: Duchenne muscular dystrophy Left: No staining around the rim of any muscle fibers Right: No staining of most muscle fibers   One "revertant" fiber with dystrophin staining.
from Novocastra Western blot of dystrophin from dystrophinopathies. Lane 1: Becker dystrophy; Dystrophin has reduced abundance but normal size. Lane 2: Becker dystrophy; Dystrophin has reduced size and abundance. Lane 3: Normal; Dystrophin has normal size and amount. Lane 4: Duchenne dystrophy; Almost no protein is present. Lane 5: Duchenne outlier; Dystrophin has severely reduced abundance.