DERMATOMYOSITIS: IMPP Adult-onset Pattern (Also see IMPP)

Immune myopathies with perimysial pathology (IMPP)
  Inflammation: Perivascular & Perimysial
  Internal architecture
  Mitochondrial staining
  Necrotic fibers invaded by cells: Acid phosphatase
  Perifascicular atrophy & Pathology
  Perimysial pathology: Alkaline phosphatase

Dermatomyositis: Childhood DM-VP pattern

General features

Muscle Fiber Pathology

H&E stain
  • Necrotic & Regenerating muscle fibers in perifascicular regions
  • Muscle fiber size is variable

Muscle Fiber Internal Architcture

NADH stain
  • Muscle fibers near the perimysium are small & stain darkly

Hydrolytic enzyme stains

Acid phosphatase stain

Acid phosphatase stained cells
in necrotic muscle fibers

Alkaline phosphatase stain

Alkaline phosphatase stained
perimysial connective tissue

Inflammation: Perimysial

H&E stain

Acid phosphatase stain
  • Cells may be confined to the perimysium (Left)
  • Acid phosphatase stain highlights some perimysial cellularity (Right).

Mitochondrial stains

Cytochrome oxidase stain

Muscle fibers in regions of perifascicular atrophy,
retain COX activity unlike the childhood pattern

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