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: Myopathy & Pathology
  Perimysial pathology: Alkaline phosphatase

Dermatomyositis: Childhood DM-VP pattern

Clinical presentations
General features

Muscle Fiber Pathology

VvG stain
Necrotic & Regenerating muscle fibers
  Most in perifascicular regions

H&E stain

Acid phosphatase stain
  • Necrotic & Regenerating muscle fibers in perifascicular regions
  • Muscle fiber sizes: Variable
Acid phosphatase stained cells
replace necrotic muscle fibers

Alcian blue stain
IMPP Myopathololgy: Necrotic & Immature (Regenerating) Muscle fibers near perimysium

Alcian blue stain

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: Immune cells (Histiocytes)

H&E stain
Histiocytes in Perimysial connective tissue (Arrow)

H&E stain

H&E stain
Histiocytes in damaged Perimysial connective tissue

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 present in some biopsies (Far right)

Acid phosphatase stain

H&E stain

Acid phosphatase stain
Perimysial Histiocytes: Scattered in connective tissue

Acid phosphatase stain

Perimysium: Damaged structure

Normal perimysium (Left)         IMPP perimysium (Right)

VvG stain

Perimysium, Damaged structure: Fragmented & Widened

Gomori trichrome stain

VvG stain

Perimysial Pathology: Alkaline Phosphatase staining

Alkaline phosphatase stain

Perimysial connective tissue: Alkaline phosphatase stained

Alkaline phosphatase stain

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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