Hereditary Neuropathy with Liability to Pressure Palsies (HNPP)

HNPP Nerve: Frozen sections

Gomori trichrome stain

VvG stain

HNPP Nerve: Fixed

Toluidine blue stain

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

Folding of myelin sheath   Outside axon or invaginating into axon

Thickened & folded myelin sheath Peripheral Schwann cell nucleus

Two axons with tomaculae One thinly myelinated large axon

HNPP: Axons & Myelin components

Neurofilament stain (Green) P0 stain (Red)

Neurofilament stain (Green) Myelin basic protein stain (Red)

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