PERIPHERAL NERVE: Chronic Demyelination

MYELIN PATHOLOGY 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)

Thinly myelinated axons. Axonal loss.	Thinly myelinated axons. Patchy axonal loss.
Onion bulbs: Small	Subperineurial edema.