CMT 1A
Nerve
![](../pics/biopsy/nerve/cmt1a/cmt1atbmp.jpg)
Toluidine blue
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Onion Bulbs
Some contain myelinated axons; Others are empty (
"Obsolete")
Myelin sheaths: Thick; Normal or Thin
Contain abundant
non-myelinating Schwann cells
![](../pics/biopsy/nerve/cmt1a/cmt1atbhp.jpg)
Toluidine blue
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Axons
Reduced numbers: Large & Small
Some onion bulbs have no axons
Some small axons are present in layers within & around onion bulbs
![](../pics/biopsy/nerve/cmt1a/cmt1anfil4mpsm.jpg)
SMI31: Neurofilament
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![](../pics/biopsy/nerve/cmt1a/cmt1anfil5sm.jpg)
SMI31: Neurofilament
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![](../pics/biopsy/nerve/cmt1a/cmt1anfilhp2.jpg)
SMI31: Neurofilament
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Schwann cells in Onion bulbs
Contain:
NCAM &
P0 protein
![](../pics/biopsy/nerve/cmt1a/cmt1ancamlp.jpg)
NCAM
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Non-myelinating Schwann cells in onion bulbs: In layers
Myelin around central axons: Abnormal; Stains for NCAM
![](../pics/biopsy/nerve/cmt1a/cmt1ancam2sm.jpg)
NCAM
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Schwann cells in Onion bulbs also contain P0 protein
![](../pics/biopsy/nerve/cmt1a/cmtnfgnp0rd.jpg)
Neurofilament (Green) & P0 (Red) stains
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CMT 1A: Muscle
Fiber size
Large fibers: Hypertrophied
Small fibers: Very small; Grouped; Some pyknotic nuclear clumps
![](../pics/biopsy/nerve/cmt1a/cmt1agrpatrhe.jpg)
H&E
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![](../pics/biopsy/nerve/cmt1a/cmt1amuschelp.jpg)
H&E
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Grouped atrophy
Perimysium: Replaced by fat
![](../pics/biopsy/nerve/cmt1a/cmt1acr.jpg)
Congo red
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Small muscle fibers: Dark on NADH stain
![](../pics/biopsy/nerve/cmt1a/cmt1anadh.jpg)
NADH
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Fiber types
Large fibers: Type grouping
Small fibers: Grouped; Type 2
![](../pics/biopsy/nerve/cmt1a/cmt1aftgatp43.jpg)
ATPase pH 4.3
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Chronic changes: Perimysium is replaced by fat
![](../pics/biopsy/nerve/cmt1a/cmt1asudan.jpg)
Sudan black
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Chronic demyelination
1/18/2017