Fasciitis

FASCIITIS

Immune
Eosinophilic
Toxic

Fasciitis: Immune

H&E stain

H&E stain

Muscle & Connective tissue pathology

Lesions
- Location: Perimysium & Epimysium (not shown)
Perimysium
- Fragmented & Pale
- Cellular & Widened in some regions
Neighboring muscle fibers: Relatively unaffected.

Acid phosphatase stain

MHC Class I
Perimysium: Mild staining
Muscle fibers: Most are normal; Mild increase in some muscle fibers near perimysium
Capillaries, endomysial: Normal staining

MHC Class I stain

C_5b-9 Deposition
Perimysium: Moderate staining
Endomysium: Diffuse deposition

MHC Class I stain

Fasciitis: Perimysial Histiocytic Inflammation

H&E stain

Acid phosphatase stain

Inflammation

Cells in regions of perimysial damage
- Large nuclei & Pink cytoplasm
- Histiocytic (Acid phosphatase & Esterase positive)
Occasional regions of undamaged perimysium contain lymphocyte infiltrates (Right).

H&E stain

H&E stain

Fasciitis: MRI

Multiple regions of increased T2 signal in leg muscles (L > R)

Fasciitis: Eosinophilic (Shulman syndrome) ¹

Pathology: Muscle
- Damage
  - Perimysial connective tissue
  - Epimysial connective tissue: Histiocytes
- Cells
  - Types
    - Histiocytes (CD206+; Anti-inflammatory)
    - CD8 lymphocytes
    - Eosinophils: Eosinophil major basic protein (EMBP)+, Some patients
  - Location: Perimysium
- Muscle fibers
  - Upregulation of MHC1 & MHC2: Especially perifascicular
  - Atrophy: Some fibers