U1RNP antibodies: Muscle Pathology
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Capillary Pathology + Minimal Myopathy Active Myopathy |
Endomysial Capillary Pathology with Minimal Myopathy
Endomysial Capillaries Morphology: Large; Moderately thick wallsEndothelium
Acid phosphatase
ATPase
Ulex stain: Capillaries Large & Reduced numbers
MxA stain: Increased
C5b-9 deposition
Muscle Fibers
Morphology: Normal
MHC Class I: Increased expression
 H&E stain |
Large
Basal lamina & Endothelial cells: Prominent
Scattered through muscle
Muscle fibers
Size variation: Moderate
Smaller fibers: Intermediate size
 H&E stain |
 Gomori trichrome stain |
Large
Basal lamina & Endothelial cells: Prominent
Scattered through muscle
Muscle fibers
Size variation: Moderate
Smaller fibers: Intermediate size
 VvG stain |
 Acid Phosphatase stain |
Acid phosphatase stain
Endothelial cells
Histiocytes near capillaries
 Acid Phosphatase stain |
 Ulex stain |
Numbers: Reduced
Stain intensity: Abnormally pale
Size: Large
 Ulex stain |
 Ulex stain |
Numbers: Reduced
Stain intensity: Abnormally pale
Size: Large
 Ulex stain |
Numbers: Reduced
Stain intensity: Abnormally pale
Size: Large
Control muscle (Below): Dark staining of small capillaries
 Ulex stain |
 MxA stain |
Capillary-associated cells: Dark stain
Muscle fibers: Mild cytoplasm stain
 MxA stain |
Capillary-associated cells: Dark stain
Muscle fibers: Mild cytoplasm stain
Control muscle (Below): No staining of capillaries or muscle fibers
 MxA stain |
 C5b-9 stain |
Endomysial Capillary-associated
Muscle fibers: No staining
 C5b-9 stain |
 ATPase pH 4.3 stain |
Perimysial Connective Tissue: Replaced by fat (Above)
 ATPase pH 4.3 stain |
 NADH stain |
Muscle fibers: Mildly coarse internal architecture
 NADH stain |
 Esterase stain |
Muscle fibers: MHC1 upregulation
 MHC I stain |
Myopathy with Capillary Pathology
 H&E stain |
Capillaries
Muscle fibers
Connective tissue
Inflammation
 Gomori trichrome stain |
 VvG stain |
Capillary Pathology
 H&E stain |
 VvG stain |
 VvG stain |
Endomysial Capillaries: Acid phosphatase stains
Endothelial cells
Cells surrounding capillaries
 Acid phosphatase stain |
Endomysial Capillaries: ATPase stains endothelium
 ATPase pH 4.3 stain |
Endomysial Capillaries: Ulex lectin shows large size & Reduced numbers
 UEA-I stain |
 UEA-I stain |
Muscle Fiber Pathology
 VvG stain |
Sizes: Varied
Many immature fibers
Necrosis: Scattered fibers
Myonuclei: Large
 H&E stain |
Muscle Fiber Pathology
Necrotic fibers invaded & replaced by histiocytes
Capillary Pathology
Histiocytes neighbor capillaries
Some endothelial cells stain for acid phosphatase
 Acid phosphatase stain |
Muscle Fiber Pathology
MHC Class I: Upregulated by muscle fibers
 MHC Class I stain |
Muscle Pathology
C5b-9 stains
Muscle fibers
Cytoplasm of necrotic fibers
Surface of few fibers
Endomysial connective tissue
 C5b-9 stain |
Perimysial Connective Tissue Pathology
 H&E stain |
Perimysial Connective Tissue
Structure: Damaged
Contains: Large, Scattered Histiocytes
Stains for: Alkaline phosphatase (Below)
 Alkaline phosphatase stain |
RNP antibody: Muscle MRI
Fascia
Enhancement & edema: Especially on muscle surfaces
Muscle: Edema, Mild
 MRI: T2 |
U1-RNP: Inflammation
 H&E stain |
Lymphocytes: Surround perimysial vessel
 Gomori trichrome stain |
 VvG stain |
Lymphocytes: CD4 stains many endomysial cells
 CD4 stain |
U1-RNP: Damaged Endomysial Capillary (Arrow)
Lumen
Present
Endothelial cells
Dark, abnormal process within vessel basal lamina, surrounding lumen
Capillary Basal lamina (Arrow)
Single layer
Thicker than muscle fiber basal lamina
Pericyte: Neighboring cell (Bottom, Right)
Location: Next to vessel, Outside basal lamina
Macrophages
Location: Cells in extracellular space around capillary
Shapes: Irregular with proceses extending into extracellular space
Cytoplasm: Contain vesicles & membrane bound organelles
Muscle fiber (Bottom)
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8/26/2026