Clinical Neurophysiology

Question 1

What are the main things done in Neurophysiology?

Answer 1

• Nerve conduction studies/Electromyography (EMG)
• EEG
• Evoked potentials

Question 2

What is nerve conduction studies/Electromyography (EMG)?

Answer 2

To investigate problems of peripheral nerve and muscle

technique for evaluating and recording the electrical activity produced by skeletal muscles

Question 3

What is an EEG?

Answer 3

Electrical activity within the brain, investigate epilepsy and states of altered consciousness

a test used to find problems related to electrical activity of the brain. An EEG tracks and records brain wave patterns

Question 4

What are evoked potentials?

Answer 4

Visual and somatosensory, investigate problems in central pathways

Question 5

What are nerve conduction studies used to examine?

Answer 5

•To examine nerve function:

• Conduction velocity
• Amplitude

record at one point then another and calculate the distance between them and therefore the time taken for the impulse to travel betweent the 2 points in order to see if there is a delay

Question 6

What are sensory studies?

Answer 6

Similar technique stimulating the sensory nerve fibres in the fingers allows measurement of sensory and motor function separately

Question 7

What is the site of ulnar neuropathy?

Answer 7

Most often at the elbow

Occasionally at the wrist

Question 8

What are the effects of ulnar neuropathy?

Answer 8

• Ulnar distribution numbness - Note dorsal cutaneous branch
• Wasting of small muscles, esp FDI

Question 9

What are we looking for on exmaination?

Answer 9

Conduction block/slowing due to demyelination

Question 10

Where can the ulnar nerve be stimulated?

Answer 10

multiple points

Question 11

How can we differentiate between a root and peripheral lesion?

Answer 11

Peripheal nerve lesion you loose both motor and sensory but if you damage it by the spinal cord level you loose the motor axons but the sensory nerve bodies live outside of the spinal cord so the patient cant feel anything but when you test it the sensory response is still normal due to this and this allows use to differentiate between a root lesion and a peripheral lesion

Question 12

What does neurophysiology allow us to do?

Answer 12

Neurophysiology can investigate nerve function

Combining this with anatomy allows diagnosis of nerve entrapment and guides subsequent surgery

Question 13

What is Myaesthenia Gravis?

Answer 13

Myasthenia gravis is a rare long-term condition that causes muscle weakness

It most commonly affects the muscles that control the eyes and eyelids, facial expressions, chewing, swallowing and speaking. But it can affect most parts of the body

Antibodies to post-synaptic ACh Receptor

Decrease effectiveness of released ACh and presents with weakness, fatigue, normal sensation

Question 14

What weakness may be seen in Myaesthenia Gravis?

Answer 14

Weakness may be generalised

Often affects eyes:

• Diplopia
• Ptosis

Question 15

What is the diagnosis of Myaesthenia Gravis?

Answer 15

Detect Antibodies (takes some weeks, only +ve in 70%)

Neurophysiology:

• Repetitive stimulation
• Single fibre EMG

Question 16

What is EMG?

Answer 16

Routine EMG looks at action potentials from whole motor units

SF EMG uses filter, sensitivity and timebase settings to isolate the action potentials from individual muscle fibres within one motor unit

Question 17

How is SF EMG useful?

Answer 17

Needle can be positioned to record from two fibres within the same motor unit

Normally little variation in time of firing between two such fibres

Question 18

In NM junction disease, how does the tight relationship between fibres change?

Answer 18

In NM junction disease that tight relationship between the two is lost

Result is “jitter”.

Question 19

Why is the tight relationship lost resulting in a jitter?

Answer 19

Basic physiology:

• EPSP
• Threshold
• AP firing

ACh causes EPSP until it reaches threshold then an AP is fired but if you begin to block some post synaptic potentials then decrease of amplitude. Slight variation in threshold potential greatly effects firing in time and begins to become more random and jumps around

Only get weakness when EPSP is to weak to even reach threshold and don’t get any second one firing at all and then get a clinical weakness

Question 20

Neurophysiology can investigate the function of the ________________

Hence can diagnose conditions such as ________, ________ and guide medical treatment

Answer 20

Neurophysiology can investigate the function of the neuromuscular junction

Hence can diagnose conditions such as myaesthenia, botulism and guide medical treatment

Question 21

What do EEGs do?

Answer 21

Assess brain function

Recording electrical activity generated by cortical neurons across multiple points on the scalp

Question 22

What can we see on a EEG?

Answer 22

• Epileptic Activity
• States of consciousness - Sleep, stages of sleep
• Encephalopathy

Question 23

EEGs look at brain function to allow the diagnosis of what?

Answer 23

• Epilepsy
• Altered states of consciousness
• Non-epileptic attacks
• Facilitate medical or surgical treatment for epilepsy