Clinical neurophysiology Flashcards
What is clinical neurophysiology?
Diagnostic neurology
What are the main tests in clinical neurophysiology?
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)
How do you test sensory function using NCS?
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
How do you test motor function using NCS?
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
What does small waves on an NCS mean?
Axon loss
Causes - diabetes, alcohol
What do slow waves on an NCS mean?
Myelin loss (demyelination) Causes - autoimmune conditions eg GBS/MS
What are the most common reasons for doing NCS?
Nerve entrapments
What is an EMG?
Using a needle to puck up electrical activity from muscle
Recording activity of individual motor units
What are you looking for on an EMG?
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)
What will the NCS and EMG look like in a myopathy?
NCS normal even though patient weak
EMG shows small motor units
What is the best test for MG?
EMG
What does an EMG in MG look like and why?
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
What is an EEG?
Primarily done with seizures
Electrodes placed in specific locations on scalp
What should you ask a patient to do when recording an EEG and why?
Close eyes, hyperventilate, photic stimulation
These are activation procedures that are aimed to try and bring out abnormalities
Can help classify epilepsy syndrome
What is an intra-cranial EEG and what is it used for?
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
What are somatosensory evoked potentials looking at?
Looks at integrity of dorsal columns
Stimulates peripheral nerve and records response from somatosensory cortex using scalp electrodes like EEG
What are the main uses of somatosensory evoked potentials?
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
What do visual evoked potentials look at?
Visual pathway
Flash checkerboard pattern whilst recording over visual cortex with EEG electrodes
What is the main use of visual evoked potentials?
MS - looking for demyelination of optic nerves
What is transcranial magnetic stimulation looking at and how does it work?
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
What is the use of transcranial magnetic stimulation?
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
What is the therapeutic use of transcranial magnetic stimulation?
Used to treat depression
Why are history and examination important in clinical neurophysiology?
Decides which muscles and nerves to examine based on clinical picture and examination findings
What is a motor unit?
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
What is the timescale post axonal injury?
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
What is an interference pattern?
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
How do myopathic disorders show on interference pattern?
Full and early
Low amplitude
What is spontaneous activity?
Ask patient to relax muscle examining
Should be no movement on EMG
What are neurogenic disorders?
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
What do neurogenic disorders look like on EMG?
Bigger amplitude
If lose axons - activate fewer motor units
IP reduced - can see gaps between motor unit action potentials
Name 3 types of spontaneous activity
Fibrillation potentials
Fasciculation potentials
Complex repetitive discharge
What are fibrillation potentials and what do they mean?
Spontaneous discharge of muscle not always visible at skin
Indicate loss of innervation of muscle fibres
Always pathological
Seen in neurogenic and myopathic disorders
What are fasciculation potentials and what do they mean?
Spontaneous firing of motor unit
Isolated discharges occurring at irregular intervals
May be visible at skin
May be benign or pathological
What are complex repetitive discharges and what do they mean?
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
How does myasthenia gravis present on EMG?
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
What do NMJ disorders look like on EMG?
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
