NERVE PATHOLOGY

Question 1

What are the two nerve injury classification systems?

Answer 1

Seddon and Sunderland

Question 2

Describe Seddon nerve injury class system.

Answer 2

Neuropraxia ‘1st deg’- no structural damage to axon, recover in 1-2months
Axontomesis’2nd deg’- wallarian degeneration; endoneurial tubes good
Neurotomesis’3rd-5th deg’- axon and endoneurium involved

Question 3

Describe Sunderland nerve injury class system.

Answer 3

1st deg- conduction block and demyelination
2nd deg- axonal loss- CMAP loss in 4-5 days NMJ, SNAP loss in 8-11 days
3rd deg- axonal loss with loss of endoneurium
4th deg- axonal loss with loss of endo and peri
5th deg- axonal loss with loss of endo, peri and epineurium

Question 4

Describe the temporal course of nerve injury.

Answer 4

Day 1- no MUP, NCS evoked response distal to lesion
Day 5- no MUP, CMAP/SNAP amp decrease, increased insertional activity
2 months- increase insert, fibs/psws, no MUP, CMAP/SNAP-NR

Question 5

Describe cellular nerve injury/chromatolysis.

Answer 5

Nucleus moves to periphery- increased volume in cell body, Nissel bodies decrease (rER)-nerve fiber distal to lesion with myelin degenerates ‘wallarian degeneration(WD)-mm atrophy

Question 6

Describe what causes conduction block.

Answer 6

If blood flow not restored after compression then axons die, damage is dependent upon amount of pressure and duration; circulation runs // to axons; get 2 degree invagination of myelin over Nodes.

Question 7

With NCS how do you id conduction block?

Answer 7

stimulate above and below the level of the lesion
No response- complete CB
decreased response- partial CB

Question 8

What causes demyelination?

Answer 8

caused by decrease in thickness of myelin

or absence of myelin

Question 9

What are NCSs signs of demyelination?

Answer 9

75% < LLN for CV and >130% ULN for latency

Question 10

What causes a demyelinating mononeuropathy?

Answer 10

secondary to focal compression

Question 11

What causes a demyelinating polyneuropathy?

Answer 11

secondary to disease (DM, ETOH, GBS, MS)

Question 12

Describe the stages of nerve compression.

Answer 12

focal demyelination-CB secondary to local ischemia- axon loss ‘axontomesis’

Question 13

What is the importance of endoneurium?

Answer 13

provides highway for axon regeneration; 1-3mm/day or 1in/month

Question 14

How does axonal regeneration occur with ‘intact’ endoneurium?

Answer 14

intact axon grows 1-3mm/day-denervated mm fibers produce signal to regenerating axon-length dependent process

Question 15

How does axonal regeneration occur without intact endoneurium?

Answer 15

schwann cells proliferate to form compact cord penetrated by growing axon- axon need to find endoneurial tube; if it finds it it will grow into it/ if not then rolls up or finds incorrect fascicle (sens-motor or type 1-type 2)

Question 16

Describe axonal/nodal sprouting?

Answer 16

Axons are constantly sending out sprouts looking for demyelinated fibers: if none found then sprouts dies back-if denervated mm fibers found they innervate them
-new ratio (1:4-1:8), changes to mm fibers to type of nerve, takes 6-8 weeks to see EMG changes and increased strength, need healthy axons in area for sprouting to occur

Question 17

What would you see in myopathy?

Answer 17

commonly affect proximal LE mms, abnormal EMG and may have decreased amp for CMAP (CMAP test distal portion); normal sensory studies

Question 18

What would you see in chronic illness myopathy?

Answer 18

affect distal mms and if severe cause decreased CMAP

Question 19

Myotonic dystrophy attacks proximal or distal mms.

Answer 19

attacks distal mms