PERIPHERAL NERVE: Chronic Demyelination

Active demyelination
Onion bulbs
Segmental demyelination
Subperineurial edema: CIDP
Teased fibers


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


Differential Diagnosis
  Pseudo-Onion bulbs
Also see: CIDP
Early onion bulb formations
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.

Electron micrographs: From Robert Schmidt MD
Onion Bulbs: Obsolete
Onion bulbs
  Multiple layers of Schwann cells & basal lamina
  Associated axon is lost

Also see
  Pseudo-onion bulbs
    Schwann cells & Circumferential Axon Sprouts

Chronic Immune Demyelinating Polyneuropathy (CIDP): Adult

Remaining axons
  Thinly myelinated
  Reduced numbers
Onion bulbs: Small
Subperineurial edema
Other CIDP pathology
Sub-acute onset

Return to Normal nerve biopsies
Return to Biopsy illustrations
Return to Neuromuscular Home Page
Return to Nerve biopsy
Return to Demyelinating neuropathies
Return to Active demyelination