Ch 5 - EDX: Pathophysiology Flashcards
What is demyelination?
Injury to myelin sheath but axon remains intact resulting in slower signal conduction
What is conduction block?
Failure of an AP to proprogate past an area of demyelination along axon that is structurally intact
How does conduction block present on NCS?
> 50% drop in CMAP amp b/w proximal and distal stimulus sites across area of injury
What are the EDX findings of Demyelination on NCS?
Prolonged latency
Dec CV
Inc temporal dispersion
Dec amp across site of injury
What are the EDX findings of Demyelination on EMG?
Normal insertional activity Normal resting activity \+/- myokymia \+/- dec recruitment Normal MUAP
What is axonal degeneration?
Degeneration of axon starts distally and ascends proximally
“Dying back”
What is Wallerian degeneration?
At site of nerve lesion, axon degenerates distally and segment intact proximal to injury
How long does Wallerian degeneration take?
Motor axons: 7 days
Sensory axons: 11 days
What are the EDX findings of axonal injury on NCS?
Normal latency
Dec amp
Normal temporal dispersion
Mild dec CV
What are the EDX findings of axonal injury on EMG?
ABN insertional activity
ABN resting activity
Dec recruitment
ABN MUAP
What is collateral sprouting?
Neurite sprouts off axon of an intact motor unit to innervate denervated muscle fibers of an injured motor unit
How long does axonal regrowth take?
1 mm/day
1 inch/month
Describe regrown axons
Dec diameter
Thinner myelin
Shorter internodal distance
Describe reinnervation on EMG
Low amp
Long duration
Polyphasic potentials (nascent potentials)
What are the types of nerve injury based on Seddon Classification?
Neuropraxia
Axonotmesis
Neurotmesis
Describe Neuropraxia
Nerve compression
Axon intact
Local myelin injury
Conduction block
What is seen on NCS in Neuropraxia?
Signal normal distal to lesion
ABN proximal/across lesion
What is seen in EMG in Neuropraxia?
Normal/dec recruitment
Describe Axontmesis
Nerve crush injury
Axonal disruption
CT/Scwann cell intact
Conduction failure
What is seen on NCS in Axontmesis?
No conduction proxmial/distal to lesion wk-months after injury
What is seen on EMG in Axonotmesis?
ABN activity
Describe Neurotmesis
Nerve transection injury
Axonal interruption
CT disruption
Conduction failure
What is seen on NCS in Neurotmesis?
No conduction proximal/distal to lesion after 2 weeks
What is seen on EMG in Neurotmesis?
ABN activity
What is the Suderland Classification of nerve injury
Type 1: conduction block Type 2: Axonal injury Type 3: type 2+ endoneurium injury Type 4: type 3+ perineurium injury Type 5: type 4+ epineurium injury
What is remyelination?
New myelin produced by Schwann cells to repair demyelinated region
What is seen on NCS with remyelination?
CV improves but slower than normal
How are neuromas formed?
If CT not intact to guide proper nerve growth
