NERVE PATHOLOGY Flashcards
What are the two nerve injury classification systems?
Seddon and Sunderland
Describe Seddon nerve injury class system.
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
Describe Sunderland nerve injury class system.
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
Describe the temporal course of nerve injury.
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
Describe cellular nerve injury/chromatolysis.
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
Describe what causes conduction block.
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.
With NCS how do you id conduction block?
stimulate above and below the level of the lesion
No response- complete CB
decreased response- partial CB
What causes demyelination?
caused by decrease in thickness of myelin
or absence of myelin
What are NCSs signs of demyelination?
75% < LLN for CV and >130% ULN for latency
What causes a demyelinating mononeuropathy?
secondary to focal compression
What causes a demyelinating polyneuropathy?
secondary to disease (DM, ETOH, GBS, MS)
Describe the stages of nerve compression.
focal demyelination-CB secondary to local ischemia- axon loss ‘axontomesis’
What is the importance of endoneurium?
provides highway for axon regeneration; 1-3mm/day or 1in/month
How does axonal regeneration occur with ‘intact’ endoneurium?
intact axon grows 1-3mm/day-denervated mm fibers produce signal to regenerating axon-length dependent process
How does axonal regeneration occur without intact endoneurium?
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)
Describe axonal/nodal sprouting?
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
What would you see in myopathy?
commonly affect proximal LE mms, abnormal EMG and may have decreased amp for CMAP (CMAP test distal portion); normal sensory studies
What would you see in chronic illness myopathy?
affect distal mms and if severe cause decreased CMAP
Myotonic dystrophy attacks proximal or distal mms.
attacks distal mms
