Neuromuscular

PERIPHERAL NERVE: Chronic Demyelination

Active demyelination
CIDP
Hypomyelination
MMN
Onion bulbs
Segmental demyelination
Subperineurial edema
Teased fibers
Tomaculae


MYELIN PATHOLOGY


Myelin Loss


Neurofilament stain
Large & Small axons: Present; Reduced numbers

VvG stain
Myelin: Mostly absent


Toluidine blue stain
Few well myelinated axons

Toluidine blue stain
Demyelinated large axons, Scattered (Arrow)


Toluidine blue stain
    Onion bulb, Early (Arrow): Reduplicated basal lamina

Segmental demyelination




Teased fibers
  Myelination is absent or thin in
  some internodes but not others



P0-Silver stain

Myelin pathology: Multifocal motor neuropathy
  Top: Normally myelinated motor axon in muscle
  Bottom: Segmental demyelination of a motor axon in Multifocal motor neuropathy

Hypomyelinated Axons


From child with Dejerine-Sottas
 

ONION BULBS


Early onion bulb formations
Note the few extra layers of basal
lamina around several thinly
myelinated larger axons.


Electron micrograph: From Robert Schmidt MD

Toluidine blue


Toluidine blue stains of plastic nerve sections

 
Late, large onion bulbs
Abundant connective tissue
around thinly myelinated axons.
Onion bulbs may contain 0, 1,
or several axons.
Large onion bulbs
Several layers of basal lamina,
connective tissue & Schwann cells
around thinly myelinated axons.

Onion Bulbs: Obsolete
Onion bulbs with multiple layers of Schwann cells & basal lamina: Associated axon is lost


Electron micrographs: From Robert Schmidt MD


Chronic Immune Demyelinating Polyneuropathy (CIDP)





Remaining axons
  Thinly myelinated
  Reduced numbers
Onion bulbs: Small
Subperineurial edema


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10/16/2013