Clinical Neurophysiology Flashcards

1
Q

What are some clinical neurophysiology investigations?

A
  • Nerve conduction studies/Electromyography (EMG)
    • To investigate problems of peripheral nerve and muscle
  • EEG
    • Electrical activity within the brain, investigate epilepsy and states of altered consciousness
  • Evoked potentials
    • Visual and somatosensory, investigate problems in central pathways
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2
Q

What does EMG stand for?

A

Electromyography

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3
Q

What do nerve conduction studies/Electromyography (EMG) investigate?

A

Problems of peripheral nerve and muscle

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4
Q

What does EEG investigate?

A
  • Electrical activity within the brain, investigate epilepsy and states of altered consciousness
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5
Q

What does evoked potentials investigate?

A

Visual and somatosensory, investigate problems in central pathways

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6
Q

What does nerve conduction studies examine?

A
  • Conduction velocity
    • Level of myelination
  • Amplitude
    • How many working nerves
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7
Q

What does the conduction velocity in nerve conduction studies indicate?

A
  • Level of myelination
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8
Q

What does the amplitude in nerve condition studies indicate?

A

How many working nerves there are

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9
Q

How are nerve conduction studies performed?

A

Measurement of activity is taken at two different points of nerve (such as along arm) and the distance measured, this can be used to work out the conduction time and velocity

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10
Q

How are sensory studies performed?

A

Similar technique to nerve conduction studies stimulating the sensory nerve fibres in the fingers to allow for measurement of sensory and motor function separately

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11
Q

What is ulnar neuropathy?

A

disorder involving the ulnar nerve, may be caused by entrapment of the ulnar nerve

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12
Q

Where is the site of ulnar neuropathy normally?

A
  • Most often at the elbow
  • Occasionally at the wrist
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13
Q

What is the clinical presentation of ulnar neuropathy?

A

Ulnar distribution numbness

Wasting of small muscles, especially FDI

First thing that occurs with a trapped nerve in demyelination, which causes the action potential to decay and die away, progressing slowly (known as conduction block)

Conduction velocity should be measures in different parts of the nerve path, slow areas are where the neuropathy occurs

Amplitude of sensory fibres becomes small because has lost axons

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14
Q

What is seen in investigations for ulnar neuropathy?

A

First thing that occurs with a trapped nerve in demyelination, which causes the action potential to decay and die away, progressing slowly (known as conduction block)

Conduction velocity should be measures in different parts of the nerve path, slow areas are where the neuropathy occurs

Amplitude of sensory fibres becomes small because has lost axons

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15
Q

How does ulnar neuropathy impact conduction velocity?

A

Conduction velocity should be measures in different parts of the nerve path, slow areas are where the neuropathy occurs

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16
Q

How does ulnar neuropathy impact the amplitude of sensory fibres?

A

Amplitude of sensory fibres becomes small because has lost axons

17
Q

What is conduction block?

A

Demyelination, which causes the action potential to decay and die away, progressing slowly

18
Q

Do peripheral nerve lesions lose motor or sensory fibres?

A

Peripheral nerve lesion loses both motor and sensory fibres:

  • Motor cell body is in spinal cord, if cut the nerve at a point everything distal dies for motor, but proximal for sensory as cell body is outside of spinal cord
19
Q

In peripheral nerve lesions, is everything distal or proximal for motor and sensory fibres?

A

Motor cell body is in spinal cord, if cut the nerve at a point everything distal dies for motor, but proximal for sensory as cell body is outside of spinal cord

20
Q

What is done to investigate nerve function?

A

Neurophysiology combined with anatomy to allow diagnosis of nerve entrapment and guide surgery

21
Q

Compare and contrast what is seen on investigations for nerve root damage (such as C8 radiculopathy) and neuropathy (such as ulnar neuropathy)

A
  • Normal sensory response and small but slowed motor response is nerve root damage (such as C8 radiculopathy)
  • Little sensory loss and slowed motor response with muscle wasting is ulnar neuropathy
22
Q

What is myaesthenia gravis?

A

Is a condition that causes muscle weakness:

  • Antibodies to post-synaptic ACh receptor
  • Decrease effectiveness of released Ach
  • Present with weakness, fatigue, normal sensation
23
Q

What is the clinical presentation of myaesthenia gravis?

A
  • Present with weakness, fatigue, normal sensation

Weakness may be generalised, often affects eyes:

  • Diplopia (double vision)
  • Ptosis (drooping upper eye lid)
24
Q

What is the medical term for double vision?

A

Diplopia

25
Q

What is the medical term for drooping of the upper eye lid?

A

Ptosis

26
Q

What is done to diagnose myaesthenia gravis?

A
  • Detect antibodies
    • Only positive in 70%
  • Neurophysiology
    • Repetitive stimulation
    • Single fibre EMG
27
Q

What is a disadvantage and advantage of EMG?

A

Disadvantage - is invasive, using a needle electrode inserted into a muscle to record electrical activity

Advantage - does not record compound action potential, teases out individiaul motor units or even individual muscle fibres

28
Q

How much muscle fibres forms a motor unit?

A

About half a dozen (6)

29
Q

EMG can record two different fibres within the same motor unit, how should the time vary between the firing of the two fibres?

A

Very little variation

30
Q

EMG can record two different fibres within the same motor unit, what can happen to the timing of firing in disease?

A
  • In neuromuscular junction disease that tight relationship between the two is lost, resulting in a jitter
  • This is due to basic physiology
    • EPSP
    • Threshold
    • AP firing
  • Normally more Ach is released than required to ensure threshold for firing action potential is reached, but if some end plate potentials are dropped the end plate amplitude drops and threshold is reached later on in time, causing considerable variation in time from firing the action potential
  • Timing of second in relation to first jumps around, measured as jitter
31
Q

Jitter can occur due delayed onset of fibre firing, but with worse myasthenia what can occur?

A

A complete block, weakness only occurs at this point when the end plate potential is too small to reach threshold, some of muscle fibres are not firing causing clinical weakness

32
Q

What are EEG recordings used to assess?

A

EEG recordings are used to assess brain function, recording electrical activity generated by cortical neurons across multiple points on the scalp

33
Q

How large an area does each EEG electrode record?

A

Each electrode records from the cortex a couple of cm in diameter beneath it:

  • About 20 electrodes taped to scalp
  • Takes about 20 minutes with the patient sitting quietly or doing something that alters brain function such as showing lights
  • Can leave on longer to look at prolonged recordings
34
Q

What can EEG be used to look at?

A
  • Epileptic activity
  • States of consciousness
    • Sleep, stages of sleep
  • Encephalopathy
35
Q

What are the two types of epilepsy?

A
  • Generalised
    • Comes about due to genetics
  • Partialised
    • Start at one part of the brain and spreads
    • Comes about due to focal lesion in the brain
36
Q

What causes generalised epilepsy?

A

Genetics

37
Q

What causes partialised epilepsy?

A

Focal lesion in the brain

38
Q

EEG looks at brain function to allow the diagnosis of what?

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