PERIPHERAL NERVE: Chronic Demyelination

  Focal, Persistent
Large nerves
Onion bulbs
Subperineurial edema: CIDP
Teased fibers


Myelin Loss: On Preserved Larger Axons

Neurofilament stain
Large & Small axons: Present; Reduced numbers

VvG stain
Myelin: Mostly absent

Myelin loss: From preserved larger axons
  Few remaining myelinated axons are small with thin myelin sheath

Toluidine blue stain
Few myelinated axons

Toluidine blue stain
Demyelinated large axons, Scattered (Arrow)
Demyelinated axons often have surrrounding Schwann cells

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

Segmental Demyelination

Segmental Demyelination (Top)
  3 short internodes with different length
Control Myelinated Axon (Bottom)
  Myelin internode: Single, Long

Teased Axons

Myelinated Axons: Segmental Demyelination
  Myelination is absent or thin in some internodes but not others

Teased Axons

Myelinated Axons: Segmental Demyelination
  Myelination of internode is thin to the left of the Node of Ranvier but normal on the right side

Teased Axons

CIDP: Distal Motor Axons
  Segmental Demyalination
  Internode widening
  Distal Axons
    Absent myelin
    Collateral sprouts: Reinnervate denervated NMJs

P0-Silver-Esterase stain

Myelin pathology: Multifocal Motor Neuropathy

P0-Silver-Esterase stain
  Above: Segmental demyelination (Arrow) of a distal motor axon in Multifocal motor neuropathy
    Arrow points to small region of myelin in area of segemental demyelination
    Fragment of neuromuscular junction (Blue stain) is at left

  Below: Normally myelinated distal motor axon in muscle
    Arrow points normal short myelin internode on distal motor axon

P0-Silver-Esterase stain

Hypomyelinated Axons

From child with Dejerine-Sottas


General features
Also see
  CMT 1
  Large nerves
Differential Diagnosis
  Pseudo-Onion bulbs

Gombault 1889

Dejerine & Sottas 1893

Onion Bulbs

Onion Bulbs, Early

Toluidine blue
Onion bulbs, thin: Around myelinated axons (Arrow)

Toluidine blue

Onion bulbs, Early
Extra layers of Basal lamina,
Collagen & Schwann cell
processes around thinly or
normally myelinated axons.

Electron micrograph: From Robert Schmidt MD
Two patterns of Early onion bulbs: Surrounding
  Thinly myelinated, around nerve fibers (Above)
    Often related to demyelination
  More thickly myelinated, irregular-shaped myelinated axons (Below)
    May be related to changes in axon size or regeneration

Toluidine blue
Onion bulbs, rudamentary (Arrows)
  Schwann cell processes & Collagen
  May partially surround irregular-shaped myelinated axons

Toluidine blue

Onion Bulbs: Large, Late

Dejerine & Sottas 1893

Toluidine blue stains of plastic nerve sections

Onion bulbs, Large
Multiple Connective tissue layers
& Schwann cell processes
around thinly myelinated axons.
Onion bulbs may contain 0, 1,
or several, axons.

Toluidine blue stains of plastic nerve sections
Onion bulbs, Large
Several layers of Basal lamina, Connective tissue & Schwann cell processess around thinly myelinated axons.

Electron micrographs: From Robert Schmidt MD
Onion Bulbs: Obsolete
Onion bulbs
  Multiple layers contain: Schwann cells alternating with collagen
  Associated axon is: Lost

Neurofilament stain (Green) + NCAM stain (Red)
Schwann cells in Onion Bulbs
  Contain both NCAM (Above) & P0 (Below) (Similar to Büngner band cells)

Neurofilament stain (Green) + P0 stain (Red)

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

Chronic Immune Demyelinating Polyneuropathy (CIDP): Adult

Other CIDP pathology
Demyelination, Active
Differential fascicular Δ
Onion bulbs
Segmental demyelination
Sub-acute onset
Thin myelin sheaths

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

Sensory CIDP: MRI

Cervical Spinal Cord & Roots: Enlargement & Contrast enhancement of Anterior & Posterior (Arrow) Roots

T1 with contrast

T1 with contrast


Enlargement of Cervical Roots & Brachial plexus (Arrow)

T1 with contrast
Contrast enhanced Lumbar Roots (Arrow)

T1 with contrast
Lumbar Roots (L4-L5)

From: Sri Krishna Alapati

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

1. Muscle Nerve 2019;59:665-670