IMPP (Also see IMPP with Jo-1 antibodies)

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

Clinical presentations
General features

Muscle Fiber Pathology

H&E stain

Acid phosphatase stain
  • Necrotic & Regenerating muscle fibers in perifascicular regions
  • Muscle fiber size is variable
Acid phosphatase stained cells
replace necrotic muscle fibers

Muscle Fiber Internal Architcture

NADH stain

Cytochrome oxidase stain
  • Muscle fibers near perimysium
    • Small
    • Stain darkly
    • Retain Cytochrome oxidase (COX) activity unlike DM-VP

MHC Class I
Often upregulated more on muscle fibers near the edge of fascicles in IMPP

MHC Class I stain

Perimysium: Abnormal staining

Alkaline phosphatase stain

Alkaline phosphatase stained
perimysial connective tissue

Perimysium: Immune cells

H&E stain

H&E stain
  • Cells
    • Often scattered selectively in perimysium
    • Large with cytoplasm and a large nucleus
    • Acid phosphatase positive
  • Acid phosphatase stain: Highlights scattered perimysial cells
  • Lymphocytes are occasionally present (Far right)

Acid phosphatase stain

H&E stain

Acid phosphatase stain

Perimysium: Damaged structure

Normal perimysium: Left;     IMPP perimysium: Right


Deposition on perimysial connective tissue extending into the endomysium
Punctate deposition on the surface of some muscle fibers

C5b-9 stain

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