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Patterns of inflammation
Perivascular Lymphocyte inflammation
![Mononuclear cell inflammation](../pics/biopsy/inflammation/pminflamv.jpg)
H&E
Lymphocytes: Perivascular May extend into perimysium
Common in BCIM
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Endomysial inflammation
![](../pics/biopsy/inflammation/inflendov.jpg)
H&E
Lymphocytes:
Often associated with focal invasion of muscle fibers
Common in IM-VAMP
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Perimysial inflammation
![](../pics/biopsy/inflammation/jo1/imppacphsm.jpg)
Histiocytes
Location: Perimysium
Stain for acid phosphatase
Common in IMPP
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Granulomatous inflammation
![](../pics/biopsy/inflammation/granuloma/granestv.jpg)
Histiocytes
Focal clusters
Endomysium or Perimysium
Granulomatous disorders
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Focal invasion of non-necrotic muscle fibers by inflammatory cells
Focal invasion of muscle fibers
Mononuclear cells
Present in: Endomysium; Focal invasion of muscle fibers
Cell Types: Lymphocytes; Histiocytes
Cell Molecular markers: KLRG1; CD8
3
Muscle fiber cytoplasm: Normal color & structure
Common in
IM-VAMP syndromes:
Inclusion body myositis &
PM-Mito
![](../pics/biopsy/inflammation/ibm/focinvhe1.jpg)
H&E stain
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Mononuclear cells
Present in: Endomysium & Focally invading muscle fibers
![](../pics/biopsy/inflammation/ibm/ibmfocinvhe2.jpg)
H&E stain
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Focal invasion of muscle fibers: Stages
![](../pics/biopsy/inflammation/ibm/focinvhehp1.jpg)
H&E stain
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![](../pics/biopsy/inflammation/ibm/focinvhehp2.jpg)
H&E stain
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![](../pics/biopsy/inflammation/ibm/focinvlonghehp.jpg)
H&E stain
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![](../pics/biopsy/inflammation/ibm/ibmfocinvrrfgtmp.jpg)
Gomori trichrome stain
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IBM: Focal Invasion of Muscle fibers by Cells
![](../pics/biopsy/inflammation/ibm/ibmfocinvgthp.jpg)
Gomori trichrome stain
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![](../pics/biopsy/inflammation/PCOXfocinvacplg.jpg)
Focal invasion of muscle fibers: Histiocytic cells
![](../pics/biopsy/inflammation/PCOXfocinvlateacp.jpg)
Acid phosphatase stain
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Focal invasion of muscle fibers in IM-VAMP: Histiocytic cells
Histiocytic cells invade muscle fiber (Arrow)
![](../pics/biopsy/inflammation/ibm/ibmfocinvacp2ar.jpg)
Acid phosphatase stain
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Focal Invasion of Muscle fibers: MHC Class I
Up-regulated by muscle fibers
Strongly expresed by mononuclear cells invading muscle fibers
![](../pics/biopsy/inflammation/ibm/focinvmhc1.jpg)
MHC Class I stain
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Features of focal invasion of muscle fibers
- Cells invade non-necrotic muscle fiber
- Commonly CD3+
- CD8+ cells
- 60% of population
- Cytotoxic
- Recognize antigens on surface membrane
- May also stain for CD57
- Autoinvasive cells are oligoclonal: Express only few types of T-cell receptors (TCR Vβ families)
- Macrophages: 20%
- CD4+ cells: 10%; Do not penetrate muscle fibers
- Monocyte chemoattractant protein-1 (MCP-1)
chemokine expression
1
- By CD3+ cells and macrophages invading non-necrotic muscle fibers
- In response to TNF-α
- During monocyte– endothelial cell interaction mediated by ICAM-1
- Remaining cytoplasm of muscle fiber appears relatively unaffected
- Invaded muscle fibers commonly
- Express HLA-I (MHC-I)
- Upregulate MMP-2 and MMP-9 on membrane
- Many normal appearing muscle fibers in same biopsy express MHC-I on surface membranes
- No binding of complement to muscle fiber (Not shown)
- Clinical correlations
- Pathology commonly associated with steroid-resistant forms of inflammatory myopathy
- Specific syndromes with prominent focal invasion of non-necrotic muscle fibers
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Necrotic Muscle Fibers
![](../pics/biopsy/inflammation/necrfib.jpg)
H&E stain
Necrosis, Early (Left)
Fiber is pale & enlarged
Internal nuclei
Invading macrophages
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![](../pics/biopsy/inflammation/phagocytest.jpg)
Esterase stain
Necrosis, Late
Fiber replaced by macrophages.
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Membrane attack complex deposition on muscle fiber surface
![](../pics/biopsy/inflammation/dmchild/c5b9fibrimhp.jpg)
Stain: C5b-9 components of complement (Membrane attack complex (MAC))
C5b-9 deposition without muscle fiber necrosis
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Major Histocompatibility Complex-1 (MHC-I) Expression in Muscle
General features
- Normal muscle
- MHC-I is expressed on capillaries but not muscle fibers
- Inflammatory myopathies & MHC-I
- Upregulation: Expressed by
- Muscle fibers on surface & cytoplasm
- Inflammatory cells
- Inclusion body myositis, Sporadic
- Diffuse expression by all muscle fibers: > 95% of patients
- Expressed by histologically normal muscle fibers
- Dermatomyositis & IMPP: Patterns of muscle fiber expression
- Diffuse: Expression on all fibers
- Selective: Muscle fibers near perimysium (perifascicular)
- SRP & HMGCR antibody myopathies
- Usually have expression mainly by regenerating muscle fibers
- Hereditary myopathies
- Usual: MHC-I is expressed on capillaries & scattered regenerating muscle fibers
- Up-regulation by muscle fibers common
![Normal: MHC-I on small vessels](../pics/biopsy/inflammation/mhc1.jpg)
Normal MHC-I on small vessels but not muscle fibers
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![Necrosis: MHC-I on phagocytic cells](../pics/biopsy/inflammation/mhc1nec.jpg)
Necrosis MHC-I on phagocytic cells in a muscle fiber
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![IBM](../pics/biopsy/inflammation/mhc1ibminfl.jpg)
Inclusion Body
Myositis
MHC-I on surface of most or all muscle fiber
MHC-I increased in cytoplasm of regenerating muscle fibers
MHC-I also stains mononuclear cells in infiltrate (Right)
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![](../pics/biopsy/inflammation/ibm/ibmmhc1b.jpg)
MHC Class I stain
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References
1. Neurology 2002;58:1779–1785
2.
Neurology 2017 Aug 9
3.
Brain 2019;142:2590-2604
7/3/2021