Ch 5 - EDX: Pathophysiology Flashcards

1
Q

What is demyelination?

A

Injury to myelin sheath but axon remains intact resulting in slower signal conduction

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2
Q

What is conduction block?

A

Failure of an AP to proprogate past an area of demyelination along axon that is structurally intact

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3
Q

How does conduction block present on NCS?

A

> 50% drop in CMAP amp b/w proximal and distal stimulus sites across area of injury

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4
Q

What are the EDX findings of Demyelination on NSC?

A

Prolonged latency
Dec CV
Inc temporal dispersion
Dec amp across site of injury

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5
Q

What are the EDX findings of Demyelination on EMG?

A
Normal insertional activity
Normal resting activity
\+/- myokymia
\+/- dec recruitment
Normal MUAP
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6
Q

What is axonal degeneration?

A

Degeneration of axon starts distally and ascends proximally

“Dying back”

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7
Q

What is Wallerian degeneration?

A

At site of nerve lesion, axon degenerates distally and segment intact proximal to injury

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8
Q

How long does Wallerian degeneration take?

A

Motor axons: 7 days

Sensory axons: 11 days

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9
Q

What are the EDX findings of axonal injury on NSC?

A

Normal latency
Dec amp
Normal temporal dispersion
Mild dec CV

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10
Q

What are the EDX findings of axonal injury on EMG?

A

ABN insertional activity
ABN resting activity
Dec recruitment
ABN MUAP

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11
Q

What is collateral sprouting?

A

Neurite sprouts off axon of an intact motor unit to innervate denervated muscle fibers of an injured motor unit

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12
Q

How long does axonal regrowth take?

A

1 mm/day

1 inch/month

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13
Q

Describe regrown axons

A

Dec diameter
Thinner myelin
Shorter internodal distance

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14
Q

Describe reinnervation on EMG

A

Low amp
Long duration
Polyphasic potentials (nascent potentials)

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15
Q

What are the types of nerve injury based on Seddon Classification?

A

Neuropraxia
Axonotmesis
Neurotmesis

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16
Q

Describe Neuropraxia

A

Nerve compression
Axon intact
Local myelin injury
Conduction block

17
Q

What is seen on NSC in Neuropraxia?

A

Signal normal distal to lesion

ABN proximal/across lesion

18
Q

What is seen in EMG in Neuropraxia?

A

Normal/dec recruitment

19
Q

Describe Axontmesis

A

Nerve crush injury
Axonal disruption
CT/Scwann cell intact
Conduction failure

20
Q

What is seen on NSC in Axontmesis?

A

No conduction proxmial/distal to lesion wk-months after injury

21
Q

What is seen on EMG in Axonotmesis?

A

ABN activity

22
Q

Describe Neurotmesis

A

Nerve transection injury
Axonal interruption
CT disruption
Conduction failure

23
Q

What is seen on NSC in Neurotmesis?

A

No conduction proximal/distal to lesion after 2 weeks

24
Q

What is seen on EMG in Neurotmesis?

A

ABN activity

25
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 ```
26
What is remyelination?
New myelin produced by Schwann cells to repair demyelinated region
27
What is seen on NCS with remyelination?
CV improves but slower than normal
28
How are neuromas formed?
If CT not intact to guide proper nerve growth