Neuromuscular

CHRONIC PARTIAL DENERVATION OF MUSCLE

Internal nuclei
Necrotic & Clustered muscle fibers
Pseudomyopathic changes
Pyknotic nuclear clumps
Regenerating axonal clusters
Split muscle fibers
Fiber type grouping

PSEUDOMYOPATHIC CHANGES


H&E stain

Gomori Trichrome stain
  • Increased endomysial connective tissue
  • Internal nuclei: One or several in many muscle fibers
  • Pyknotic nuclear clumps
  • Grouped atrophy of muscle fibers
    • Groups are less well demarcated than in ongoing denervation
    • Increased endomysial connective tissue is especially prominent in these regions
  • Small muscle fibers may be rounded or angular
  • Hypertrophic muscle fibers are common


SPLIT MUSCLE FIBERS

INTERNAL NUCLEI


H&E stain

NADH stain

H&E stain
  • "Split" muscle fibers probably result from partial fusion of regenerating fibers
  • These split muscle fibers are very large (hypertrophic)
  • Split muscle fibers often have internal nuclei


FIBER TYPE GROUPING


ATPase stain, pH 9.4
See: Fiber type grouping

NECROTIC & CLUSTERED MUSCLE FIBERS


H&E stain
  • A hypertrophied muscle fiber may become necrotic (left)
  • Several different muscle fibers regenerate in its place and cluster within the old basal lamina


PYKNOTIC NUCLEAR CLUMPS


H & E stains

NADH stain

Esterase stain
  • Definition
    • Clumps of myonuclei are the end product of denervation atrophy without reinnervation.
    • The remainder of the myofiber, such as the contractile apparatus and most of the cytoplasm, has largely disappeared.
  • Histochemical staining
    • Nuclei: Basophilic on H & E
    • Muscle fiber: Dark on NADH & esterase

REGENERATING AXONAL CLUSTERS


Toluidine blue stain




Also see: Fiber type grouping, Grouped atrophy: Large & Ongoing denervation


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9/23/2004