Neuromuscular

Focal demyelination: Chronic

  No, or little, remyelination
  Probably at region of persistent temporal dispersion



Toluidine blue stain
Myelinated axons
  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
Demyelinated axons
  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




Electron micrographs: From Robert Schmidt MD
Axons: Chronic demyelination
  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

Schwann cell processes
  Surround demyelinated axon
  Have associated basal lamina

Electron micrographs: From Robert Schmidt MD


Electron micrographs: From Robert Schmidt MD
Hypomyelinated axons
  Surrounded by few, or multiple, Schwann cell processes

Electron micrographs: From Robert Schmidt MD

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7/27/2016