Muscle Fiber Necrosis

MUSCLE FIBER NECROSIS

General features
Necrosis & Rhabdomyolysis
Stages
Early Features
Metabolic damage
Sarcolemmal membrane damage
Macrophage activation
Fixed muscle, Paraffin sections
Later features
Phagocytosis & Regeneration
Myofiber collapse
Eosinophils
Etiologies
Immune
BCIM
HMGCR myopathy
Macrophage activation
SRP myopathy
Phosphorylase deficiency
Statin toxicity
Distribution of Necrotic fibers
Clustered
Immune (Vascular)
Regional Ischemic Immune
Hereditary (Stretch-induced)
Myopathic grouping
Perifascicular: IMPP
Scattered
Necrosis: Types & Features
Metabolic failure
Membrane damage

Segmental Necrosis of Muscle fibers: Varied stages

Necrosis: General features & Stages ¹

Cell & Metabolic Morphology Metabolic failure Membrane damage Variant Phagocytosis	Early Stages
	Myofiber Necrosis Metabolic Muscle Fiber cytoplasm: Pale Myonuclei: Lose staining	Myofiber Necrosis Sarcolemmal Membrane Muscle Fiber Cytoplasm "C" or Δ Lesion Regional Hypercontraction
	Later Stages
	Myofiber Necrosis Phagocytic Late Muscle Fiber: Replaced by macrophages.	Myofiber Necrosis Collapse Very Late Muscle Fiber space: Collapse, Few remaining histiocytes Macrophages have migrated away

Necrosis: Cellular & metabolic changes
- Cytoplasmic swelling (oncosis)
- Rupture of plasma membrane
- Cytoplasmic organelles: Swelling; Loss
- Chromatin: Condensation, moderate
- Absent: Apoptotic & Autophagic markers
- Necrosis in muscle
  - Associated with either
    - Metabolic failure: Ca⁺⁺ leak into cytoplasm
    - Break in, or loss of, muscle surface fiber membrane
  - Results in: Irreversible damage to whole, or segment of, muscle fiber
  - All organelles involved
- Associated metabolic alterations
  - No common biochemical denominator
  - Mitochondrial
    - Uncoupling
    - Production of reactive oxygen species (ROS)
    - Mitochondrial membrane permeabilization: Often controlled by cyclophilin D
    - Ca⁺⁺ overload
  - Lysosomal
    - ROS production by Fenton reactions
    - Membrane permeabilization
  - Nuclear
  - Lipid degradation
    - Activation of phospholipases, lipoxygenases & sphingomyelinases
  - Ca⁺⁺
    - Activation of non-caspase proteases: Calpains; Cathepsins

Necrotic muscle fiber morphology: Metabolic failure
- Myofiber changes: Sarcolemma & Cytoplasm
  - H & E and Gomori Trichrome
    - Cytoplasm staining: Pale
    - Intermyofibrillar network: Absent
    - Myonuclei: Absent or reduced staining
  - Necrotic muscle fibers have reduced or absent staining with
    - NADH
    - Mitochondrial (SDH)
    - Myosin ATPase
  - Necrotic muscle fibers: Molecular & cellular markers
    - Cytoplasm of necrotic muscle fibers
      - C_5b-9 Complement (Memebrane attack complex (MAC))
      - IgM
      - Ca⁺⁺: Increased in necrotic muscle fibers
    - Around the rim of necrotic muscle fibers: Alkaline phosphatase
    - Muscle fiber phagocytosis
      - Histiocytic (Phagocytic) cells stain for: Acid phosphatase; Esterase; HAM56; CD68; MHC Class I
  - Ultrastructure
    - Loss of plasma membrane
    - Myofibrils: Lysed or Lost
    - Mitochondria: Abnormal
    - Late: Granular or filamentous debris in fibers
  - Rare in intrafusil muscle fibers
Necrotic muscle fiber morphology: Membrane damage
- Early damage pattern: Delta lesion
- Necrosis: Muscle fiber cross-sections contain pale & hypercontracted regions
Necrosis variant: Regulated necrosis (Necroptosis)
- Programmed cell death
- Stimuli
  - TNF-α : Pro-necrotic in muscle fibers
  - Death domain receptors: TNFR1 , Fas/CD95 , TRAIL-R
  - Toll-like receptors: TLR3 , TLR4
- Pathway: Kinase RIP1 (RIPK1)
  - Molecules upregulated: RIPK1 , RIPK3 , MLKL
  - Execution pathway
    - RIP1–RIP3 necroptotic complex
    - Production of mitochondrial reactive oxygen species (ROS)
    - Depletion of cell energy under apoptotic-deficient conditions
  - Caspase-independent
- Histologic marker: phospho-MLKL
Necrosis in muscle: Stages
- Early necrosis: Patterns
  - Cytoplasmic pallor: "Metabolic" pattern
  - Sectoral lesion & Hypercontraction
  - Subsarcolemmal lesion
- Phagocytosis (Clean-up) of necrotic muscle fibers
  - Early: Infiltration of muscle fibers by histiocytic cells
    - Proliferation or Migration of Phagocytic cells
    - Attraction of Phagocytic cells to necrotic muscle fiber
    - Phagocytosis of necrotic muscle fibers
    - Associated macrophages: M1 type
      - Classically activated inflammatory macrophages
      - Infiltrate at early time points after injury
      - Generate inflammatory cytokines
      - Sustain activation & proliferation of muscle stem cells
  - Late: "Collapse"
    - Migration of macrophages away from necrotic muscle fiber
    - "Collapse" of region with necrotic muscle fiber
- Cell remnant disposal
  - Related enzyme: MAP kinase phosphatase-1 (MKP-1; DUSP1)
- Cell proliferation
  - Muscle precursors
    - Function: Formation of regenerating muscle fibers
    - Origins
      - Satellite (Stem) cells
      - Vessel-associated muscle stem cells (Mesoangioblasts)
        
        Myogenic precursors
        
        Express pericyte markers
        
        Cross vessel walls
  - Connective tissue & Fat: Fibro/adipogenic progenitors (FAPs)
    - Sustain satellite cell-driven myogenesis
    - May differentiate into myoblasts, adipocytes or fibroblasts
  - M2 macrophages
  - Presence: Associated with tissue "Inflammation"
  - Late: Muscle healing
    - FAPs & Stem cells undergo apoptosis

Muscle Fiber Necrosis (Rhabdomyolysis episode): Morphology

Segmental necrosis: Scattered necrotic & hypercontracted muscle fibers

H & E Stain	Normal muscle fiber
	Necrotic muscle fiber: Pale; Little phagocytosis
	Necrotic muscle fiber: Phagocytosis by macrophages
	Hypercontracted necrotic muscle fiber
	Perimysium

Necrosis: Early; Metabolic failure
Pale muscle fibers with loss of cytoplasmic structures & staining

H&E stain
Necrotic muscle fibers: Pale; Little phagocytosis (Arrows)
Gomori trichrome stain	H&E Necrotic muscle fiber, Early Fiber is pale & enlarged. Internal nuclei may reflect invasion by macrophages.

Necrosis: Early; "Metabolic" pattern
Muscle fiber cytoplasm: Pale
Nuclear staining: Absent

Gomori trichrome stain

Necrotic muscle fibers: Internal architecture has lost NADH staining (Arrow)

NADH stain

Rhabdomyolysis
Some non-necrotic muscle fibers have increased lipid (Left)
Phagocytic cells have only minor staining of their cytoplasm (Right)

Sudan black stain

Necrosis: Early; Membrane damage, Statin toxicity
Varied internal structure: Hypercontracted material & Palor in different areas of single fibers

H&E stain

Membrane damage at several regions of individual fibers: Associated with clear regions in cytoplasm

H&E stain

H&E stain

"C"- or "Delta"-lesions
Membrane & Neighboring cytoplasm damage in a focal region of individual muscle fibers: Pale staining
Cytoplasm around focal lesion stains dark

H&E stain

NADH stain

"C"- or "Delta"-lesions
Cytoplasm around focal lesion stains pale

NADH stain

Congo red stain

Phagocytosis of Muscle fibers
Histiocytic cells invade & replace muscle fibers

H&E stain
Necrotic muscle fibers: Phagocytosis (Arrows)
Gomori trichrome stain

Necrotic muscle fiber
Largely replaced by cells
Some remaining debris

H&E stain

NADH stain

Phagocytic cells within pale necrotic muscle fibers
Phagocytic cells have
Mild NADH staining
Strong esterase staining
Necrotic muscle fibers: Cytoplasm has little, or no, staining

Esterase stain

Acid phosphatase stain
Necrosis: Varied Stages
Early: Pale stained muscle fibers
Later: Muscle fibers progressively replaced by acid phosphatase + cells (Right)

Acid phosphatasae stain

Esterase stain
Necrotic muscle fiber, Late
Muscle fiber is invaded and
replaced by phagocytes.

Esterase stain

Necrosis & Phagocytosis: Late

H&E stain

Phagocytic cells
Replace necrotic muscle fibers
Move out of necrotic muscle fiber areas

Acid phosphatasae stain

H&E stain

Collapsed, phagocytosed muscle fibers
Space occupied by necrotic muscle fibers "Collapses"
Some histiocytes remain

Acid phosphatase stain

MHC Class I stain
Very late stage necrosis: MHC Class I
Stains remaining cells phagocytsing collapsed muscle fibers
Stains capillaries (Normal)
No staining of most muscle fibers (Normal)

Alkaline phosphatase stain
Necrosis: Alkaline phosphatase stains around the rim of muscle fibers

Toluidine blue stain Necrotic muscle fiber (Longitudinal section) Pale Invaded by cells
Toluidine blue stain Necrotic muscle fiber (Cross-section) Pale Invaded by cells	Toluidine blue stain Necrotic muscle fiber Pale Invaded by cells

Toluidine blue stain
Cells in necrotic fiber

Toluidine blue stain
Non-necrotic, abnormal muscle fiber (Left): Dilated SR

Necrotic muscle fibers: Complement C5b-9 (MAC) deposition

Stain: C5b-9 components of complement (Membrane attack complex (MAC))
Necrosis: C_5b-9 deposition diffusely within muscle fiber cytoplasm

Rhabdomyolysis: PAS stain is pale in small & large muscle fibers

Necrosis: Ongoing

Necrosis: Early stage
Pale muscle fiber cytoplasm
Lipid droplets
Two other muscle fibers have large lipid droplets but are not pale & necrotic

H&E stain

H&E stain

Necrosis: Phagocytosis of varying degrees

H&E stain

Necrosis associated with Eosinophils

Unusual: Eosinophils may be a component of cells replacing necrotic muscle fibers
Reported with LGMD 2A (Calpain-3 mutations)

H&E stain

H&E stain

Gomori trichrome stain

H&E stain

H&E stain

H&E stain

Necrosis: Scattered Muscle fibers

H&E stain

Necrotic Muscle Fibers: Scattered
Ongoing: Muscle fibers in varied stages of necrosis & regeneration
Also see: Scattered necrosis, Severe

H&E stain

Necrotic Muscle Fibers: Scattered
Monophasic: Scattered muscle fibers in early stage of necrosis
Cytoplasm of Necrotic Muscle fibers stains diffusely for C_5b-9

C_5b-9 stain stain

Also see: Regional Ischemic Immune Myopathy

Return to Neuromuscular Home Page

References
1. Cell Death Differ 2016 Feb 12

10/18/2017

MUSCLE FIBER NECROSIS

Necrosis: General features & Stages 1

Muscle Fiber Necrosis (Rhabdomyolysis episode): Morphology

Necrotic muscle fibers: Complement C5b-9 (MAC) deposition

Necrosis: Ongoing

Necrosis associated with Eosinophils

Necrosis: Scattered Muscle fibers

Necrosis: General features & Stages ¹