Hereditary Neuropathy with Liability to Pressure Palsies (HNPP)
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Myelin patterns Tomaculae: Teased axons Ultrastructure: 1; 2 |
HNPP Nerve: Frozen sections
Axon Loss: Reduced numbers of myelinated axons
 Gomori trichrome stain |
 VvG stain |
HNPP Nerve: Fixed |
 Toluidine blue stain |
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Reduced numbers of large axons Abnormal myelination of axons includes Hypomyelination Abnormally folded (Tomaculae) or shaped myelin sheaths Small onion bulbs are also present (Below; Arrow)  Toluidine blue stain  Toluidine blue stain 
Toluidine blue stain |
 Thickened myelin sheath due to multiple layers of folded myelin |
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 Folding of myelin sheath Outside axon or invaginating into axon |
Myelin sheath: Thick & Folded Schwann cell nucleus: Peripheral |
Two axons with tomaculae One thinly myelinated large axon |
HNPP: Axons & Myelin components
Most myelinated axons are smallCompare to Normal nerve
Myelinated axons are large & small
 Neurofilament stain (Green) P0 stain (Red) |
 Neurofilament stain (Green) Myelin basic protein stain (Red) |
Compare to Normal nerve
MBP is only in sheaths around large axons
HNPP: MBP is in most myelin sheaths
Compare to Normal nerve
MBP is only in sheaths around large axons
P0 is in myelin sheaths around small & large axons
 P0 stain (Green) Myelin basic protein stain (Red) |
 Neurofilament (SMI31) stain Axon Loss Reduced numbers of large axons Relative preservation of numbers of small axon |
HNPP: Muscle |
 Gomori trichrome stain Mild atrophy |
 H& E stain Occasional: Grouped atrophy & Pyknotic nuclear clumps |
 ATPase pH 9.$ stain Fiber type grouping |
 ATPase pH 4.3 stain Fiber type grouping; Rare Type 2C muscle fiber |
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Tomaculae
Tomaculae: Ultrastructure
Return to Demyelinating neuropathies
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4/24/2024