General features
- Muscle fibers: Myopathy, ongoing
- Connective tissue
- Endomysial capillaries: Reduced number; Enlarged; C5b-9 deposition
- Immune
- Inflammation: Little or none
- MHC Class I: Often normal on muscle fibers
SRP: Early Pathology
Necrotic & Regenerating muscle fibers: Scattered
![](../pics/biopsy/inflammation/srp/srpearlyhelp.jpg)
H&E stain
|
![](../pics/biopsy/inflammation/srp/srpearlyhehp.jpg)
H&E stain
|
Muscle fibers: Necrosis & Regeneration
![](../pics/biopsy/inflammation/srp/srpearlycr2.jpg)
Congo red stain
|
![](../pics/biopsy/inflammation/srp/srpearlyacp.jpg)
Acid phosphatase stain
|
Necrotic muscle fibers: Scattered
Phagocytic cells: Stain for acid phosphatase
Cytoplasm: Stains for C
5b-9 complement
![](../pics/biopsy/inflammation/srp/srpearlyc5b9.jpg)
C5b-9 stain
|
![](../pics/biopsy/inflammation/srp/srpearlynadh.jpg)
NADH stain
|
Necrotic (pale) & Regenerating (dark) muscle fibers
![](../pics/biopsy/inflammation/srp/srpearlynadh2.jpg)
NADH stain
|
MHC Class I
Muscle fibers
Generally not expressed
Present in cytoplasm of regenerating muscle fibers
Cells: Present on histiocytic cells associated with necrotic muscle fibers
Vessels: Normally present on endomysial capillary & perimysial vessel endothelial cells
![](../pics/biopsy/inflammation/srp/srpearlymhc1.jpg)
MHC Class I stain
|
SRP: INTERMEDIATE PATHOLOGY
Muscle fiber sizes: Varied; Small to Upper limit of normal; Bimodal distribution
Small muscle fibers: Rounded; Large nuclei; Basophilic cytoplasm,
Clustered
Endomysial connective tissue:
Increased, Mild to Moderate
Perimysial connective tissue: Irregular or fragmented
Pathology distribution: Patchy; Some regions with more small muscle fibers & Increased endomysial connective tissue
![](../pics/biopsy/inflammation/srp/srpmodhelp.jpg)
H&E stain
|
Muscle damage
More severe, with increased endomysial connective tissue, in some regions
![](../pics/biopsy/inflammation/srp/srpmodhemp.jpg)
H&E stain
|
![](../pics/biopsy/inflammation/srp/srpmodhemp2.jpg)
H&E stain
|
Muscle fiber sizes: Bimodal
Small muscle fibers: Rounded; Large nuclei
Endomysial connective tissue: Mildly increased
|
|
![](../pics/biopsy/inflammation/srp/srpbimodhec3h.jpg)
H&E stain
|
![](../pics/biopsy/inflammation/srp/srpmodgtmp.jpg)
Gomori trichrome stain
|
![](../pics/biopsy/inflammation/srp/srpreggthp.jpg)
Gomori trichrome stain
|
Immature muscle fibers with large myonuclei
![](../pics/biopsy/inflammation/srp/srpimmatcr.jpg)
Congo red stain
|
Muscle fiber internal architecture
Some small muscle fibers stain dark
One necrotic muscle fiber has pale cytoplasm (Arrow)
Large fibers have coarse internal architecture
![](../pics/biopsy/inflammation/srp/srpmodnadhar.jpg)
NADH stain
|
![](../pics/biopsy/inflammation/srp/srpmodvvg.jpg)
VvG stain
|
Fiber sizes: Varied; Small fibers round
Endomysial connective tissue: Increased
Muscle fiber necrosis: Few fibers with pale-stained cytoplasm
![](../pics/biopsy/inflammation/srp/srpmodcr.jpg)
Congo red stain
|
![](../pics/biopsy/inflammation/srp/srpacpnec1h.jpg)
Acid phosphatase stain
Necrotic muscle fibers
Scattered
Pale cytoplasm
Associated histiocytic cells
|
![](../pics/biopsy/inflammation/srp/srpcellsacpch.jpg)
Acid phosphatase stain
Acid phosphatase positive cells
Scattered in endomysium
|
![](../pics/biopsy/inflammation/srp/srpmodacp.jpg)
Acid phosphatase stain
|
Necrotic muscle fibers
Scattered in muscle
![](../pics/biopsy/inflammation/srp/srpnecc5b9.jpg)
C5b-9 stain
|
C5b-9 Deposition
Necrotic muscle fibers
Distribution: Scattered
Cytoplasm: Diffuse C
5b-9 stain
Endomysial capillaries: Some patients
![](../pics/biopsy/inflammation/srp/srpmodc5b9lp2.jpg)
C5b-9 stain
|
SRP myopathy: Immature muscle fibers
Many muscle fibers persist in immature states
![](../pics/biopsy/inflammation/srp/srpmodalplp2.jpg)
Alkaline phosphatase stain
|
Muscle fiber immaturity
Properties
Many small immature muscle fibers stain for alkaline phosphatase
Many small & large muscle fibers are type 2C (Below)
Distribution in muscle: Immature, small fibers are often
clustered
![](../pics/biopsy/inflammation/srp/srpmodatp43lp.jpg)
ATPtase pH 4.3 stain
|
Immature Muscle Fibers: Clustered
![](../pics/biopsy/inflammation/srp/srpclustregatp43.jpg)
ATPtase pH 4.3 stain
|
![](../pics/biopsy/inflammation/srp/srpclustreghemp.jpg)
H&E stain
|
![](../pics/biopsy/inflammation/srp/srpclustreggthp2.jpg)
Gomori trichrome stain
|
Small clusters of Immature muscle fibers
![](../pics/biopsy/inflammation/srp/srpclustregvvg.jpg)
VvG stain
|
![](../pics/biopsy/inflammation/srp/srpclustregnadhhp.jpg)
NADH stain
|
Small clusters of Immature muscle fibers
![](../pics/biopsy/inflammation/srp/srpclustregalp.jpg)
Alkaline phosphatase stain
|
![](../pics/biopsy/inflammation/srp/srpclustpathgt.jpg)
Gomori trichrome stain
|
Focal Regions of Muscle fiber Damage
![](../pics/biopsy/inflammation/srp/srpclustpathvvg.jpg)
VvG stain
|
SRP Myopathy, Moderate
Perimysial Pathology
![](../pics/biopsy/inflammation/srp/srpperimysfraggtmp.jpg)
Gomori trichrome stain
|
Perimysium
Fragmented
No cells
![](../pics/biopsy/inflammation/srp/srpperimysfragvvgtmp.jpg)
VvG stain
|
![](../pics/biopsy/inflammation/srp/srpctpathvvg.jpg)
VvG stain
|
SRP Myopathy, Moderate
Myofiber Basal Lamina Pathology
![](../pics/biopsy/inflammation/srp/srpmerosinlp.jpg)
Laminin-α2 stain
|
SRP Muscle fiber basal lamina: Thickened & Irregular on large & small fibers
Control Muscle fiber basal lamina
![](../pics/biopsy/inflammation/srp/merosincontlp.jpg)
Laminin-α2 stain
|
SRP: LATE, SEVERE PATHOLOGY, Months
Muscle fiber sizes: Varied; Small to Mildly large
Small muscle fibers: Rounded; Large nuclei; Basophilic cytoplasm
Endomysial connective tissue: Increased, Moderate to Marked
Pathology distribution: Patchy; Some regions with more endomysial connective tissue & only small rounded muscle fibers
![](../pics/biopsy/inflammation/srp/srpsevhelp.jpg)
H&E stain
|
![](../pics/biopsy/inflammation/srp/srphypertc.jpg)
H&E stain
Increased endomysial connective tissue Hypertrophic and small muscle fibers
|
![](../pics/biopsy/inflammation/srp/srpctgtsmc.jpg)
Gomori trichrome stain
Many small rounded muscle fibers Increased endomysial connective tissue
|
![](../pics/biopsy/inflammation/srp/srpfibhe2.jpg)
H&E stain
Endomysial connective tissue: Marked increase
Disease course of only 6 months
|
![](../pics/biopsy/inflammation/srp/srpsevhemp.jpg)
H& E stain
|
Endomysial connective tissue Marked increase
More in some fascicles than others
![](../pics/biopsy/inflammation/srp/srpsevvvg2.jpg)
VvG stain
|
![](../pics/biopsy/inflammation/srp/srpsevvvg.jpg)
VvG stain
|
Endomysial connective tissue: Marked increase
![](../pics/biopsy/inflammation/srp/srpsevgthp.jpg)
Gomori trichrome stain
|
![](../pics/biopsy/inflammation/srp/srpsevatp43.jpg)
ATPase pH 4.3 stain
|
Many muscle fibers retain immature features
Type 2C on ATPase pH 4.3 stain
Cytoplasm stains for alkaline phosphatase
![](../pics/biopsy/inflammation/srp/srpsevalp.jpg)
Alkaline phosphatase stain
|
Histiocytic (red stained) cells in endomysial connective tissue
![](../pics/biopsy/inflammation/srp/srpsevacp.jpg)
Acid phosphatase stain
|
MHC Class I
Normal on muscle fibers: No staining
Present on endomysial cells
![](../pics/biopsy/inflammation/srp/srpsevmhc1.jpg)
MHC Class I stain
|
SRP Myopathy, Severe
Myofiber Basal Lamina Pathology
![](../pics/biopsy/inflammation/srp/srpsevlama2.jpg)
Laminin-α2 stain
|
Muscle Fiber Basal lamina: Thickened & Irregular (Above) vs control (Below)
![](../pics/biopsy/inflammation/srp/srpsevlama2cont.jpg)
Laminin-α2 stain
|
SRP: LATE, MILD PATHOLOGY, Months
![](../pics/biopsy/inflammation/srp/srpmildchronhelp.jpg)
H&E stain
|
Muscle fiber sizes: Varied; Small angular fibers, Scattered
Small muscle fibers: Angular; Basophilic cytoplasm
Endomysial connective tissue: Increased, Mild
![](../pics/biopsy/inflammation/srp/srpmildchronhemp.jpg)
H&E stain
|
![](../pics/biopsy/inflammation/srp/srpmildchronvvg.jpg)
VvG stain
|
Histiocytic cells: Scattered in endomysium
![](../pics/biopsy/inflammation/srp/srpmildchronacp.jpg)
Acid phosphatase stain
|
![](../pics/biopsy/inflammation/srp/srpmildchronatp43.jpg)
ATPase pH 4.3 stain
|
Many muscle fibers retain immature features
Type 2C on ATPase pH 4.3 stain
Cytoplasm stains for alkaline phosphatase
![](../pics/biopsy/inflammation/srp/srpmildchronalp.jpg)
Alkaline phosphatase stain
|
![](../pics/biopsy/inflammation/srp/srpmildchronc5b9.jpg)
C5b-9 stain
|
Necrotic muscle fibers: Scattered (with C
5b-9 stained cytoplasm)
MHC Class I: Not prominent on muscle fibers
![](../pics/biopsy/inflammation/srp/srpmildchronmhc12.jpg)
MHC Class I stain
|
Neuromuscular junctions: Normal
![](../pics/biopsy/inflammation/srp/srpmildchronest.jpg)
Esterase stain
|
SRP MYOPATHY: CAPILLARY PATHOLOGY
![](../pics/biopsy/inflammation/srp/srpcaplp.jpg)
Ulex europaeus agglutinin I stain
SRP myopathy
Endomysial capillaries: Large & Mildly reduced in number
Some muscle fibers have no adjacent capillary
|
![](../pics/biopsy/inflammation/srp/srpcaphp2.jpg)
Ulex europaeus agglutinin I stain
SRP myopathy
Endomysial capillaries: Large
|
![](../pics/biopsy/inflammation/srp/nlcaphp.jpg)
Ulex europaeus agglutinin I stain
Normal muscle
Endomysial capillaries: Small
All fibers have adjacent capillaries
|
![](../pics/biopsy/inflammation/srp/srpulexsm.jpg)
Ulex europaeus agglutinin I stain
|
SRP MYOPATHY: MEMBRANE ATTACK COMPLEX (C5b-9)
In cytoplasm of scattered necrotic muscle fiber
On some capillaries
|
![](../pics/biopsy/inflammation/srp/c5b9.jpg)
Antibody vs C5b-9
C5b-9
Deposition in endomysial capillaries and
necrotic muscle fiber cytoplasm (Arrow)
|
![](../pics/biopsy/inflammation/srp/compdephp.jpg)
Antibody vs C5b-9
C5b-9
Irregular deposition in endomysial capillaries (Arrows)
|
Return to
Inflammatory myopathies
Return to
SRP myopathy
4/26/2023