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LGMD 2A: Calpain-3 deficiency

Child   Chronic myopathy   Immune features   Fiber types: Large 2 & 2C   Fat accumulation   Myopathic grouping   Necrosis   Regeneration   Splitting

Adult   Chronic myopathy   Myopathic grouping   Varied fiber size   Necrosis   Regeneration   Fiber types

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LGMD 2A: Child

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Myopathic changes

Myopathic Features
  Muscle Fibers
    Sizes: Varied
      Large fibers: Hypertrophied
      Small fibers: Round or Polygonal; Basophilic cytoplasm common
    Myopathic groups
  Endomysial connective tissue
    Mildly increased in some regions

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H&E stain Myopathy   Muscle fiber sizes: Varied   Split muscle fibers   Increased endomysial connective tissue

H&E stain Myopathic groups   Clustered basophilic fibers (Arrow)

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Muscle Fiber Splitting

H&E stain Split muscle fiber (Arrow)   Small fibers in region of split fiber are clustered

NADH stain Split muscle fiber (Arrow)   Split is highlighted by NADH stain   "Splitting" is actually partial fusion

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Muscle Fiber Necrosis: Myopathic Grouping

Clusters of Muscle fibers: All in early & similar stage of necrosis

H&E stain Pale muscle fiber (Arrow) invaded by cells

Acid phosphatase stain Acid phosphatase-stained cells within pale necrotic muscle fibers

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Cluster of Muscle fibers: All in early & similar stage of necrosis
  Muscle fibers are: Pale-stained (Arrow); Some invaded by cells

VvG stain

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Muscle Fiber Types

ATPase, pH 9.4 stain Most large fibers are Type 2

ATPase, pH 4.3 stain Type 2C (intermediate staining) fibers are abundant

ATPase, pH 9.4 stain

Most large muscle fibers: Type 2 (Dark)
Small fibers: Both types
Fiber type distribution: Non-random (Clusters of type 1 & type 2 fibers are present)

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Immune features

Eosinophils
  Scattered in perimysium in regions of muscle fiber necrosis

H&E stain Endomysial inflammation, minor

MHC Class I stain Normal distribution of MHC Class I: Only on capillaries

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Fat accumulation in perimysium

Sudan black stain

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LGMD 2A: Adult

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Myopathic changes: Varied involvement in different fascicles

H&E stain Varied fiber sizes Little necrosis or regeneration

H&E stain Varied fiber size Abundant necrosis and regeneration

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Myopathic Groups

Large group of small basophilic   muscle fibers with large nuclei H&E stain	Small muscle fibers have coarse   internal architecture NADH stain
Small muscle fibers are type 2C   with intermediate staining ATPase, pH 4.3 stain	Small muscle fibers are immature   with alkaline phosphatase staining Alkaline phosphatase stain

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Fiber types

ATPase, pH9.4 stain Small & large size fiber populations contain type I & type II

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10/14/2022