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IMPP (Also see IMPP with Jo-1 antibodies)

Immune myopathies with Perimysial Pathology (IMPP) DM-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
  • Onset age: Adult more common than Childhood
• Dermatomyositis: With weakness & skin rash
• Immune myopathy: With weakness, but no skin rash
• Myalgia syndrome: With high aldolase but normal strength & serum CK
• Interstitial lung disease
• Arthritis

General features

• Clinical & Pathologic classification: Immune myopathies with Perimysial Pathology
  • Also see: Jo-1 antibody-related IMPP
• Onset age: More common in adults
• Pathology
  • Perimysial damage: Common
  • Muscle fiber necrosis
    • More in perifascicular muscle fibers
    • More common than in DM-VP
  • Cytochrome oxidase: No reduction in muscle fibers

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Muscle Fiber Pathology

VvG stain

Necrotic & Regenerating muscle fibers
  Most in perifascicular regions

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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

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Muscle Fiber Internal Architcture

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

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

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Perimysium: Immune cells (Histiocytes)

H&E stain

Histiocytes in Perimysial connective tissue (Arrow)

H&E stain

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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

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Perimysium: Damaged structure

Normal perimysium (Left)         IMPP perimysium (Right)

VvG stain

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Perimysium, Damaged structure: Fragmented & Widened

Gomori trichrome stain

VvG stain

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Perimysial Pathology: Alkaline Phosphatase staining

Alkaline phosphatase stain Perimysial connective tissue: Alkaline phosphatase stained

Alkaline phosphatase stain

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C5b-9 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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3/3/2021