Focal demyelination: Chronic
No, or little, remyelination
Probably at region of persistent temporal dispersion
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Demyelinated axons Hypomyelinated axons Axon loss |
 Toluidine blue stain |
Focal endoneurial region with reduced numbers
Demyelinated axons are common in this area
Remaining myelinated axons often have thin myelin
 Toluidine blue stain |
Region of nerve with chronic demyelination but little or no remyeliation
Many completely demyelinated axons
Schwann cells & their processes surrounding the demyelinated axons
Phagocytosis of myelin is complete: No histiocytes or myelin debris
This pathology is likely associated with a region of
chronic partial conduction block or temporal dispersion on electrodiagnostic testing
 Electron micrographs: From Robert Schmidt MD |
 Nerve conduction studies (Median nerve) Temporal dispersion |
Axons
No surrounding myelin
Cytoplasm is dark & contains closely spaced neurofilaments.
Some myelinated axons may remain in the same area (Right)
Schwann cells & their processes
Surround the demyelinated axons
May be multiple Schwann cells around single axon
 Electron micrograph: From Robert Schmidt MD |
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 Electron micrographs: From Robert Schmidt MD |
No myelination around axon
Schwann cell processes
Multiple
Surround axon
No onion bulbs
Lipofuscin debris (Arrow)
Usually only present in non-myelinating Schwann cells
 Electron micrographs: From Robert Schmidt MD |
 Nerve conduction studies (Ulnar nerve) Temporal dispersion NCV: Moderate slowing |
 Electron micrographs: From Robert Schmidt MD |
Surround demyelinated axon
Have associated basal lamina
 Electron micrographs: From Robert Schmidt MD |
 Electron micrographs: From Robert Schmidt MD |
 Electron micrographs: From Robert Schmidt MD |
Surrounded by few, or multiple, Schwann cell processes
 Electron micrographs: From Robert Schmidt MD |
Loss of Small Axons: Collagen Pockets
(Same nerve as above)
 Electron micrographs: From Robert Schmidt MD |
 Electron micrographs: From Robert Schmidt MD |
Pi Granules
 Electron micrographs: From Robert Schmidt MD |
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4/7/2021