Ch 5 - EDX: Pathophysiology

Question 1

What is demyelination?

Answer 1

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

Question 2

What is conduction block?

Answer 2

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

Question 3

How does conduction block present on NCS?

Answer 3

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

Question 4

What are the EDX findings of Demyelination on NCS?

Answer 4

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

Question 5

What are the EDX findings of Demyelination on EMG?

Answer 5

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

Question 6

What is axonal degeneration?

Answer 6

Degeneration of axon starts distally and ascends proximally

“Dying back”

Question 7

What is Wallerian degeneration?

Answer 7

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

Question 8

How long does Wallerian degeneration take?

Answer 8

Motor axons: 7 days

Sensory axons: 11 days

Question 9

What are the EDX findings of axonal injury on NCS?

Answer 9

Normal latency
Dec amp
Normal temporal dispersion
Mild dec CV

Question 10

What are the EDX findings of axonal injury on EMG?

Answer 10

ABN insertional activity
ABN resting activity
Dec recruitment
ABN MUAP

Question 11

What is collateral sprouting?

Answer 11

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

Question 12

How long does axonal regrowth take?

Answer 12

1 mm/day

1 inch/month

Question 13

Describe regrown axons

Answer 13

Dec diameter
Thinner myelin
Shorter internodal distance

Question 14

Describe reinnervation on EMG

Answer 14

Low amp
Long duration
Polyphasic potentials (nascent potentials)

Question 15

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

Answer 15

Neuropraxia
Axonotmesis
Neurotmesis

Question 16

Describe Neuropraxia

Answer 16

Nerve compression
Axon intact
Local myelin injury
Conduction block

Question 17

What is seen on NCS in Neuropraxia?

Answer 17

Signal normal distal to lesion

ABN proximal/across lesion

Question 18

What is seen in EMG in Neuropraxia?

Answer 18

Normal/dec recruitment

Question 19

Describe Axontmesis

Answer 19

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

Question 20

What is seen on NCS in Axontmesis?

Answer 20

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

Question 21

What is seen on EMG in Axonotmesis?

Answer 21

ABN activity

Question 22

Describe Neurotmesis

Answer 22

Nerve transection injury
Axonal interruption
CT disruption
Conduction failure

Question 23

What is seen on NCS in Neurotmesis?

Answer 23

No conduction proximal/distal to lesion after 2 weeks

Question 24

What is seen on EMG in Neurotmesis?

Answer 24

ABN activity

Question 25

What is the Suderland Classification of nerve injury

Answer 25

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

Question 26

What is remyelination?

Answer 26

New myelin produced by Schwann cells to repair demyelinated region

Question 27

What is seen on NCS with remyelination?

Answer 27

CV improves but slower than normal

Question 28

How are neuromas formed?

Answer 28

If CT not intact to guide proper nerve growth