Metachromatic Leukodystrophy (MLD) (& Krabbe)

Myelin sheath thin: TB; EM
Onion bulbs
Prismatic inclusions (Macrophages)
Schwann cell debris
Tuffstone bodies

Metachromatic Leukodystrophy (MLD)

Hypomyelinated axons

Metachromatic Leukodystrophy (MLD)
  Myelinating Schwann cells
    Contain cytoplasmic particulate & clear debris.

  Axons surrounded by
    Thin myelin sheaths & Onion bulbs, small.

Myelinating Schwann cells
  Contain particulate & clear debris in cytoplasm
Onion Bulbs: Small

MLD Histochemistry

H&E stain
  Increased space between axons

H&E stain

Gomori trichrome stain
Reduced staining for myelinated axons

Gomori trichrome stain

Larger axons
  Increased space between axons

VvG stain

Larger axons: Normal to mildly reduced numbers
Smaller axons: Reduced numbers in some endoneurial areas

MLD: Reduced or Absent Myelin Sheath

Unmyelinated axons: Surrounded by Schwann cells

Axons with thin, or folded, myelin sheath
Onion bulb: Small, single layer of basal lamina around axons & Schwann cells

MLD: Schwann cell inclusions

Axons: Moderately or Severely thin myelin sheath
Schwann cells: Contain myeloid debris in secondary lysosomes

Schwann cells: Cytoplasm contains Tuffstone inclusions & Myeloid debris

Schwann cells with Cytoplasmic inclusions

MLD: Tuffstone Bodies

Tuffstone bodies
  Electron dense: Sharply demarcated
  Most common in Schwann cells of myelinated & unmyelinated axons
    Irregularly oriented granular material
    Areas with 5.8 nm periodicity
    Peripheral lamellae oriented perpendicular to surface
    Vacuoles: Electon lucent

Tuffstone bodies

MLD: Macrophages

Prismatic ("Herringbone") inclusions
  Commonly in endoneurial macrophages
  Stacks of lamellar disks

MLD: Muscle

Muscle fiber sizes: Mild variation; No denervation

Muscle fiber types
  Fiber type grouping: Mild
  Type 2C: Increased numbers

Krabbe disease: Globoid cells

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