Clinical neurophysiology

Question 1

What is clinical neurophysiology?

Answer 1

Diagnostic neurology

Question 2

What are the main tests in clinical neurophysiology?

Answer 2

Nerve conduction studies and electromyography - PNS (motor neuron, root, nerve, NMJ, muscle)
Electroencephalography - brain
Evoked potentials
- Somatosensory evoked potentials (sensory pathways - dorsal columns)
- Visual evoked potentials (visual pathways - central)
- Transcranial magnetic stimulation (motor pathways)

Question 3

How do you test sensory function using NCS?

Answer 3

Electrical stimulation making outside of nerve negative
Inside therefore positive by comparison - triggers action potential which moves down nerve
Record with sticky electrodes
Measure size of response and speed

Question 4

How do you test motor function using NCS?

Answer 4

Electrical stimulation induces action potential
AP reaches NMJ causing ACh release
Ach activates AchRs on muscle causing muscle to contract and see visible twitch
Measure size of response and speed

Question 5

What does small waves on an NCS mean?

Answer 5

Axon loss

Causes - diabetes, alcohol

Question 6

What do slow waves on an NCS mean?

Answer 6

Myelin loss (demyelination)
Causes - autoimmune conditions eg GBS/MS

Question 7

What are the most common reasons for doing NCS?

Answer 7

Nerve entrapments

Question 8

What is an EMG?

Answer 8

Using a needle to puck up electrical activity from muscle

Recording activity of individual motor units

Question 9

What are you looking for on an EMG?

Answer 9

Big motor units (nerve/motor neuron pathology) - nerves take over motor units of lost muscles therefore size of motor neurons increase
Can look for small motor units (muscle pathology)

Question 10

What will the NCS and EMG look like in a myopathy?

Answer 10

NCS normal even though patient weak

EMG shows small motor units

Question 11

What is the best test for MG?

Answer 11

EMG

Question 12

What does an EMG in MG look like and why?

Answer 12

When two muscle fibres next to each other contract the time between each other their contractions remains the same whereas in MG neuromuscular transmission time between contractions varies and get overlapping waves - called jitter

Question 13

What is an EEG?

Answer 13

Primarily done with seizures

Electrodes placed in specific locations on scalp

Question 14

What should you ask a patient to do when recording an EEG and why?

Answer 14

Close eyes, hyperventilate, photic stimulation
These are activation procedures that are aimed to try and bring out abnormalities
Can help classify epilepsy syndrome

Question 15

What is an intra-cranial EEG and what is it used for?

Answer 15

Used in patients being worked up for epilepsy surgery due to medically intractable seizures ie medication doesn’t work
Helps to ascertain exactly where seizures arise from

Question 16

What are somatosensory evoked potentials looking at?

Answer 16

Looks at integrity of dorsal columns

Stimulates peripheral nerve and records response from somatosensory cortex using scalp electrodes like EEG

Question 17

What are the main uses of somatosensory evoked potentials?

Answer 17

MS - demyelination slows impulses so response recorded from scalp is delayed
Intra-operative monitoring eg spinal cord surgery - if cord is compromised response gets smaller then is lost, aim to warn surgeon before its too late

Question 18

What do visual evoked potentials look at?

Answer 18

Visual pathway

Flash checkerboard pattern whilst recording over visual cortex with EEG electrodes

Question 19

What is the main use of visual evoked potentials?

Answer 19

MS - looking for demyelination of optic nerves

Question 20

What is transcranial magnetic stimulation looking at and how does it work?

Answer 20

Place magnet over motor cortex and record from contralateral muscle
Brief magnetic pulse induces an electrical current that excites cells in motor cortex
Fire down motor pathway - can record a response from a limb muscle - motor evoked potential

Question 21

What is the use of transcranial magnetic stimulation?

Answer 21

Looks at integrity of pathways connecting motor cortex and targets muscle
- Can subtract out peripheral nerve components so looks selectively at central motor pathways
- Can also look at excitability of motor cortex
MND, MS

Question 22

What is the therapeutic use of transcranial magnetic stimulation?

Answer 22

Used to treat depression

Question 23

Why are history and examination important in clinical neurophysiology?

Answer 23

Decides which muscles and nerves to examine based on clinical picture and examination findings

Question 24

What is a motor unit?

Answer 24

Basic functional elements of PNS
- Anterior horn cell
- Axon
- NMJ
- Muscle fibres
Number of muscle fibres innervated by a single motor neuron varies between muscles

Question 25

What is the timescale post axonal injury?

Answer 25

1/7 to 2/52
- Normal/near normal distal NCS (EMG likely abnormal)
- Poor recruitment on EMG, reduced pattern
3/52
- NCS decreased amplitude or absent (fibs on EMG)
4-6/52
- Nascent potentials on EMG
3/12
- Some chronic neurogenic EMG changes
2 years
- Little further improvement expected clinically or in NCS parameters

Question 26

What is an interference pattern?

Answer 26

Ask patient to minimally contract muscle examining
Recruitment of all motor units to the point that no single motor unit action potential can be distinguished
Judged by eye or quantitate based on number of turns per second
Should be no space between waves if there is - loss of motor units

Question 27

How do myopathic disorders show on interference pattern?

Answer 27

Full and early

Low amplitude

Question 28

What is spontaneous activity?

Answer 28

Ask patient to relax muscle examining

Should be no movement on EMG

Question 29

What are neurogenic disorders?

Answer 29

Arising from nerves (MN - root - axon)
Could be traumatic, toxic, metabolic or hereditary
Findings depend on temporal relationship between injury and examination and degree of reinnervation from other nerves

Question 30

What do neurogenic disorders look like on EMG?

Answer 30

Bigger amplitude
If lose axons - activate fewer motor units
IP reduced - can see gaps between motor unit action potentials

Question 31

Name 3 types of spontaneous activity

Answer 31

Fibrillation potentials
Fasciculation potentials
Complex repetitive discharge

Question 32

What are fibrillation potentials and what do they mean?

Answer 32

Spontaneous discharge of muscle not always visible at skin
Indicate loss of innervation of muscle fibres
Always pathological
Seen in neurogenic and myopathic disorders

Question 33

What are fasciculation potentials and what do they mean?

Answer 33

Spontaneous firing of motor unit
Isolated discharges occurring at irregular intervals
May be visible at skin
May be benign or pathological

Question 34

What are complex repetitive discharges and what do they mean?

Answer 34

Start and stop abruptly
Constant frequency
Stereotyped group of single fibre potentials with complex morphology
Probable ephaptic transmission between adjacent muscle fibres
Seen predominantly in neurogenic disease

Question 35

How does myasthenia gravis present on EMG?

Answer 35

When 2 muscle fibres next to each other contract the time between each of their contractions remains the same
Bloods less accurate than EMG
In MG neuromuscular transmission - time between contractions of 2 muscle fibres varies - jitter

Question 36

What do NMJ disorders look like on EMG?

Answer 36

Single fibre EMG
Jittering
Not specific
Denervation-reinnervation can also result in immature collateral nerve terminals and instability of neuromuscular transmission
Can see in ALS
Use alongside clinical symptoms to diagnose