F- Electrophysiological Examinations.ppt

EMG/NCS
Electroencephalography (EEG)
Evoked potentials/ Event Related Potentials

1. Electrophysiological
Examinations
EMG/NCS
Electroencephalography (EEG)
Evoked potentials/ Event Related Potentials

2. EMG/NCS
Electromyography
Nerve Conduction Studies

3. .
Electromyography (EMG)
•The pattern of electrical activity in muscle
both at rest and during activity
–recorded from a needle electrode inserted
into the muscle.
–Evaluates individual motor units by
inserting electrode into muscle
–nature and pattern of abnormalities relate
to disorders at different levels of the
motor unit.

4. .
1.Insertional activity:
Brief burst of AP following insertion into
resting muscle.
2. Spontaneous activity:
Normal resting muscle has no spontaneous
activity except end-plate noise.
a. Configuration = duration, amplitude,
number of phases
1) Duration: Long or Short
2) Amplitude: High
3) Polyphasic:

5. .
b. Recruitment: Effort recruits additional
motor units.
c. Fibrillations: Spikes, positive sharp
waves.
d. Fasciculations: Discharge of an entire
Motor Unit.
e. Myotonia, myokymia: Complex
repetitive discharges.

6. .
Nerve conduction studies (NCS)
Measure electrical conduction along a nerve
1. Motor NCS: Stimulate motor nerve and
record muscle CMAP (compound muscle
action potential), i.e., the sum of all axons
directed to the muscle.
a. Amplitude: Reflects the number of
conductive muscle fibers (therefore axons)
b. Distal latency: Time between stimulus and
recording, depends on conduction of axons
(not NMJ or muscle).
c. Conduction velocity: Divides the distal
latency between two locations along the same
nerve by the distance between them

7. Medical Physiology Principles for Clinical Medicine.chw

8. .
2. Sensory NCS:
•Stimulate a nerve and record its sensory nerve
action potential (SNAP) from purely sensory
portion of the nerve.
–E.g sural nerve is purely sensory.
3. Late responses:
a.F-wave: Motor stimulus travels both ortho-
and antidromically.
Antidromic stimulus reflected through neuron
and back; creates small F-wave seen after
first (M) wave.
F-wave delay
b. H-reflex: CMAP from stimulation of sensory
nerve, via monosy naptic reflex arc.

9. .
4. Repetitive stimulation: Abnormalities are
hallmark of NMJ dz.
a.Myasthenia: repetitive 3-Hz stimulation
results in decrement of CMAP ; With
exercise, CMAP can improve for first
min, but then worsen in 4-6 min
b.c. Botulism: Baseline CMAP smaller with
repetitive stimulation; no change with
exercise.

10. EMG findings in neuromuscular diseases.
  Conduction
Velocity
AmplitudeF & H
Latency
Distal
Latency
Fibrillations
Axonal damage >70% ↓ ~↑ nl ↑
PNS demyelination<50% ~↓ ↑ ~↑Variable
LMN dz >70% ↓ motor~c nl ↑
UMN dz nl nl nl nl None
Radiculopathy >80% ~↓ ↑ nl ↑
NMJ dz nl nl/↓ nl nl None
Myopathy nl ~↓ nl nl None

11. Electroencephalography
(EEG)
..

12. EEG
A.What is EEG/Electroencephalography?"
B.What does the EEG tell us?
1.General health of the brain
2.Epilepsy

13. .
A. What is EEG/ Electroencephalography?"
•Measuring of brain waves
•The electrical activity of the brain is easily
recorded from electrodes placed on the
scalp.
•The potential difference between pairs of
electrodes on the scalp (bipolar derivation)
or between individual scalp electrodes and
a relatively inactive common reference
point (referential derivation)

14. EEG cont'd
•Harmless and painless investigation
•Takes ~20-30 minutes
•Some provocation method used
–Hyperventilation
–Photic stimulation
–Sleep deprivation-sleep EEG

15. EEG cont'd
Electrodes are put on the scalp
Measure the difference in potentials
between two points on the scalp.
oGenerally 21 electrodes and two
references on ears applied according to
proscribed system
oPen deflections represent differences in
electrical potentials between the two
electrodes involved in a given channel

16. EEG cont,d

17. From Wyllie
EEG cont,d

18. EEG cont,d

19. Unipolar vs.
Bipolar montage

20. EEG cont,d
Types of waves
Alpha
Beta
Theta
Delta
Normal variations
Age,
Sleep,
Epileptiform
discharges
Sharp waves
Spikes
Spike-wave
complexes

21. Beta: >13 Hz;usually diffuse low
Voltage:increase with sedatives,
Light sleep
Alpha: 8-12 Hz; the posterior basic rhythm;
At age 3 reaching 8 Hz; at age 10, 10 Hz
Abnormal if amplitude asymm. >50%
Theta: 4-7 Hz; small amts. nl; increases
With drowsiness, hyperventilation
Delta: 0-3 Hz; posterior slow waves of youth
Nl; normal in sleep; focal delta=local abnl.
? At grey/white junction; post-ictal
The Frequencies

22. EEG cont,d
B. What does the EEG tell us?
1- General health of the brain
–“Vital signs”
–Encephalopathy
–Focal pathology
2- Epilepsy -are there seizure activity?
–Ictal activity
–Interictal activity
•With or without specific provocation

23. EEG cont,d
1. General health of the brain
1a. “Vital signs”
–Posterior basic rhythm
–Background fast activity
–Background slow activity
–Sleep activity
•Signs from various sleep stages
•Arousals from sleep
–Nearly all have age-appropriate norms

24. normal
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25. FP1-F7
F7-T3
T3-T5
T5-O1
FP2-F8
F8-T4
T4-T6
T6-O2
FP1-F3
F3-C3
C3-P3
P3-O1
FP2-F4
F4-C4
C4-P4
P4-O2
1 sec 100 µV
Rhythmic temporal theta bursts of drowsiness

26. Spindles

27. POSTS

28. EEG cont,d
1b. Encephalopathy
–Metabolic (e.g., triphasic waves)
–Infectious (e.g., meningitis)
–Toxic (e.g., drug overdose)
–Anoxia/hypoxia
EEG: usually generalized findings (e.g.,
diffuse loss of normal background
activity)

29. EEG cont,d
1c. Focal pathology – e.g.
–Tumor, Stroke, Bleeds, fluid collections,
etc
–Certain infections (e.g., HSV
encephalitis)
–Malformations of cortical development
–Brain injury
–Degenerative disorders
EEG: focal slowing or loss of fast activity;
may see focal spikes or sharp waves

31. EEG cont,d
2. Epilepsy- seizure disorders
Ictal activity
oGeneralized vs. focal seizure patterns
Interictal activity
oSpikes, sharp waves, hypsarrhythmia
Provocative maneuvers
oSleep
oHyperventilation
oIntermittent photic stimulation
Clarification/ Classification of seizure
disorders/status

32. EEG demonstrating a couplet of left anterior temporal spike-
and-slow waves.

34. POLYSPIKE WAVE

35. Evoked potentials/ Event
Related Potentials
.

36. EPs reflect neurophysiological processing
along the pathways from sensation to
primary sensory cortex
EPs develop 1–150 milliseconds after
presentation of the stimulus used to
evoke them
the exact timing (latency) of the EP after
stimulus delivery dependent on the
location of its neural generators along the
processing pathway in which it is evoked

37. Filter & Amplify
Average across
Trials &
Individuals
Collapsed to
form a “Grand
Average” Or
mean of means
Electrical activity
at the onset of a
stimulus
recorded

38. Single Trial: 100ms visual
stimulus
Average of 200 trials to
same stimulus
ERP derived from EEG

39. Stimulation may be visual, auditory, or
somatosensory.
Visual EPs-the patient is exposed to flashing
lights or a checkerboard pattern.
Auditory EP-the patient hears a specific tone.
Somatosensory EP- the patient experiences an
electrical stimulation to an extremity.
Stimuli occur repeatedly while the patient
undergoes a routine EEG.

40. •Brainstem auditory evoked
responses (BAERs)
–Early waves after an auditory stimulus
–Reflect the intactness of the pathways
they traverse and thus are of great
interest to neurologists.

42. Visual Evoked Potentials(VEP)
–Potentials after an visual stimulus
–Shows the intactness of the visual
pathway
•From retina to occipital cortex.

44. Event-related brain potentials
(Cognitive Evoked Potentials)
A non-invasive method of measuring brain
activity during cognitive processing
ERPs reflect the information processing in
the cortex in real time
Are recorded from the human scalp
Are “Electrical Potentials associated with
specific sensory, perceptual, cognitive, or
motor events”

45. .
ERPs -used to distinguish psychological and
neural sub-processes involved in complex
cognitive, motor, or perceptual tasks
–reflect the information processing in the
cortex in real time
P300-P3 (component of the ERP)
Approximately 300–400 ms after onset of
an auditory target stimulus
Related to the cognitive aspects of
distinguishing an infrequently occurring
target stimulus from other stimuli occurring
more frequently

47. A wave showing several ERP components,
including the N100 and P300

48. .
Useful in
 Neurology and neurosurgery. –in
epilepsy, in multiple sclerosis (MS)
 Psychiatry- differentiation of organic
from functional impairments e.g. hysterical
blindness
Not applicable for all areas of psychology
e.g.
P3 component is
Prolonged in latency in many patients with
dementia
Normal in patients with depression or other
psychiatric disorders