Neuropathies, nerve injury and diagnostic technique

Question 1

What is a peripheral neuropathy?

Answer 1

damage/disease affecting PNS nerve
impair sensation, movement, gland or organ function

sensory nerve = tingling, pain, numbness

motor nerve = weakness to hands and feet

autonomic nerves (involuntary) - change HR/BP

Question 2

What is mono/polyneuropathy?

Answer 2

mono - single nerve affected
poly - several nerves being affected

causes are metabolic, toxic, inflammatory, traumatic, genetic
30% idiopathic

Question 3

What is neuropraxia?

Answer 3

compression in axon - no discontinuity (endoneurium intact)

recoverable conduction block

Question 4

What is axonotmesis?

Answer 4

demyelination and axon loss (epineurium and perineurium intact)
degeneration to fibre
possibly unrecoverable

Question 5

What is neurotmesis?

Answer 5

most severe form of nerve injury
complete nerve division/disruption
damage to epineurium (around entire nerve - no nerve growth)

Question 6

Describe the process of nerve cell injury?

Answer 6

1. Injury causes inflammation- phagocytes destroy myelin and axon
2. Wallerian degeneration - causes cell body changes (chromatolysis)
3. Stumps grown from axon to muscle fibre again (long distance axon regeneration)
4. substantial recovery can occur in adult PNS neurons

Question 7

What is a neuroma?

Answer 7

when axon doesnt find final position

Question 8

What a root avulsion?

Answer 8

if dorsal - still intact as maintained by cell body

if ventral - degeneration (detached from cell body)

Question 9

What is needle EMG?

How to distinguish between myopathy or denervation?

Answer 9

distinguish between myopathies (intrinsic to muscle) and muscle weakness due to nerve pathology (neurogenic)

look at waveform of MOTOR UNIT ACTION POTENTIALS

• myopathy signals are smaller and fibrillate (muscle fibres damaged)
• neurogenic signals are larger (other nerves take over), denervated muscle fibres fibrillate

Question 10

What do we see in fibres 3 and 1/5?

Answer 10

3 - large response, closest to electrode

Question 11

What is a nerve conduction study?

Answer 11

diagnostic technique to evaluate speed of nerve impulses

1. stimulate muscle with electrode
2. electric field of electrode penetrates skin and stimulated nerve (median nerve in hand)
3. surface EMG recorded (milliV)

• nerve conduction velocity (m/s)
• amplitude of responses (mv)
• help identify axonopathies/demyelinating neuropathies

Question 12

What axonopathies/demyelinating neuropathies affect?

How are they detected on an EMG?

Answer 12

1 - amplitude of response, reduced responses

2 - conduction, more proximal response delayed

In GBS (both cases) - delayed and reduced amplitude

Question 13

What is somatosensory evoked potential?

Answer 13

• stimulate nerves and place electrodes in specific locations
• if there is a lesion/block in somatosensory pathways (PNS or CNS) assess amplitude or latency of response (e.g. MS)

microV

Question 14

What is needed for SEP?

Answer 14

many (100) responses that are averaged

• there is a small amplitude of nerve responses (microV)
• average to negate noise
• compared to mV looking at muscle in surface EMG