Neuromuscular

Congenital Hypomyelinating Neuropathy

4 y.o. Female: PMP-22 point mutation


H&E stain
Endoneurium
  No large myelinated axons
  Cellular
  Some increased connective tissue space
Perineurium & Endoneurium: Normal

H&E stain

Gomori trichrome stain
Endoneurium
  No large myelinated axons
Perineurium & Endoneurium: Normal

VvG stain

Neurofilament stain
Endoneurium
  Large axons: Many
  Small axons: Normal to Reduced Numbers

Neurofilament stain


Toluidine blue stain
Endoneurium
  Large axons: Thinly myelinated; Reduced numbers
  BLOBs: Increased space around axons (Arrow; Below)
  Fibroblasts: Scattered; Long processes

Toluidine blue stain

Toluidine blue stain
Endoneurium
  Large axons: Thinly myelinated; Reduced numbers
  BLOBs: Increased space around axons
  Fibroblasts (Arrows)
    Scattered
    Long processes
    Some processes around outside of BLOBs

Toluidine blue stain

Basal Lamina Onion Bulbs (BLOBs)

BLOB Structure
  Basal Lamina
    Concentric thin fragments (Arrow), Double-layered
    Around larger axons
  Collagen: Between layers of basal lamina
  Schwann cell processes
    Few
    Within layers of basal lamina
    Center of BLOB: May immediately surround axon
  Myelin: Present around some axons
  Fibroblasts: Process may surround BLOB
BLOB Structure
  Basal Lamina
    Concentric thin fragments (Arrow), Double-layered
    Surround larger axons
  Collagen: Between layers of basal lamina
  Schwann cell processes
    Few
    Within layers of basal lamina
    Center of BLOB: May immediately surround axon
  Myelin: Present around some axons
  Fibroblasts: Process may surround BLOB (Arrow)

BLOBs: Surround Unmyelinated & Hypomyelinated Axons

6 Axons (Left to Right)
  1. Far left: Small axon, part, surrounded by Schwann cell process with external basal lamina
  2. Left: Small-Intermediate-sized axon surrounded by dark Schwann cell processes
  3. Left-Center (BLOB): Intermediate-sized, unmyelinated axon with surrounding layers
        Inner: Schwann cell processes (Dark) directly around axon; No associated myelin
        Intermediate
          Double layers of Schwann cell Basal Lamina; Each extends partly around axon
          Two very small Schwann cell processes (Left) are present within individual layers of Schwann cell basal lamina
        Outer
          Double basal lamina (Above)
            Partially contains a Schwann cell process
            Schwann cell process extends from a Schwann cell that surrounds 2 unmyelinated axons
          Fibroblast process,partial (Left of Basal lamina layers)
  4. & 5. Right-Center: 2 Small axons: Surrounded by Schwann cell processes
  6. Right Upper: Larger axon surrounded by
    Thin myelin sheath layer
    BLOB: Double layers of circumferential basal lamina

BLOBs: Surround Unmyelinated Axons
BLOB
  Center: Intermediate-sized, unmyelinated axon with surrounding layers
  Inner layer
    Schwann cell processes (Dark): Directly around axon; No associated myelin
    Schwann cell nucleus: Near axon
  Intermediate layers
    Double layers of Schwann cell Basal Lamina; Each extends partly around axon
  Outer layer
    Fibroblast process,partial (Left of Basal lamina layers)
    Collagen particles

BLOB
  Center: Intermediate-sized, unmyelinated axon with surrounding layers
  Inner layer
    Schwann cell processes (Dark): Directly around axon; No associated myelin
    Schwann cell nucleus: Near axon
  Intermediate layers
    Double layers of Schwann cell Basal Lamina; Each extends partly around axon

BLOBs: Basal laminal layers around Axon with Incomplete, Thin Myelin Layer
BLOB
  Center: Intermediate-sized axon with surrounding layers
  Inner layer
    Schwann cell processes (Dark): Directly around axon; Incomplete layer of associated myelin
  Intermediate layers
    Double layers of Schwann cell Basal Lamina; Each extends partly around axon
    Schwann cell processes: Few present (Contain basal lamina)
  Outer layer: May contain fibroblast processes (Right)

BLOBs: Around Axon with Thin Myelin Layer (Hypomyelination)
BLOB
  Center: Intermediate-sized, Hypomyelinated axon with surrounding layers
  Inner layer
    Myelin sheath: Thin
    Schwann cell cytoplasm: Directly around part of myelin
    Schwann cell nucleus: Near axon
  Intermediate layers
    Double layers of Schwann cell Basal Lamina; Each extends partly around axon
  Outer layer
    Fibroblast nucleus & processes (Above; Right)
    Collagen particles

BLOB
  Center: Intermediate-sized, Hypomyelinated axon with surrounding layers
  Inner layer
    Myelin sheath: Thin
    Schwann cell cytoplasm: Directly around part of myelin
  Intermediate layers
    Double layers of Schwann cell Basal Lamina; Each extends partly around axon
    Schwann cell processes within some basal lamina
  Outer layer
    Collagen particles

BLOB: Basal Lamina, Double layer, around Thinly Myelinated Axon


From: R Schmidt

Unmyelinated Axons


From: R Schmidt
Individual Schwann cells surround several small axons

From: R Schmidt

From: R Schmidt
Individual Schwann cell surrounds several small axons
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4/28/2024