EMG

Question 1

3 EMG electrodes

Answer 1

Reference, ground, recording

Question 2

Which electrodes are typically used in
a) small animals
b) large animals

Answer 2

a) concentric
b) monopolar (sharper edge, less painful, more noise, less precise)

Question 3

Where do we place the ground electrode for:
a) Pelvic limbs
b) Thoracic limbs
c) head

Answer 3

a) Stifle
b) Olecranon
c) occipital protuberance

Question 4

Negative deflection =

Answer 4

upward

Question 5

Name the normal EMG pattenrs

Answer 5

Electrically silent
Insertional activity
Miniature end-plate potentials (mEPPs)
End plate potentials/spikes (EPPs)
Motor unit action potentials (MUAPs)

Question 6

Name the abnormal EMG pattenrs

Answer 6

Fibrillation potentials
Positive sharp waves
Complex repetitive discharges (CRDs)
Myotonic potential

Question 7

Insertional activity
1. Morphology
2. Cause (physiologic)
3. ↑ in ____
4. ↓ in ____

Answer 7

1. Abrupt start/stop, high frequency, crisp static sound
2. Dysruption of myofibers by needle insertion or movement
3. Denervation or myopathies
4. Fibrosis or atrophy

Slide 35

Question 8

Insertional activity
Start increasing at day ____ and peak at day ____ after denervation injury

Answer 8

4, 8

Question 9

mEPP
1. Morphology
2. Cause
3. Cease after ____
4. ↓ Frequency with ____
5. ↓ Amplitude with ____

Answer 9

1. Small amplitude (5-50 uV), high frequency (5-50 Hz), background activity, 1-2 ms duration, sheashell sound
2. Spontaneous post-synptic depolarizations (not AP!) due to random ACh quanta release
3. Denervation
4. Botulism
5. MG

Slide 40

Question 10

EPP/EPS
1. Morphology.
2. How to distinguish from FPs?
3. Cause

Answer 10

1. Biphasic, starting with negative (upward) deflection. Often in association with mEPPs, but larger amplitude
2. =
   - EPPs = initial upward (negative), often associated with mEPPs.
   - FP = initial downward (+), often associated with PSWs.
3. Normal spontaneous APs (vs mEPPs = depolarizations) of muscle fibers

Slide 42

Question 11

MUAPs
a) Morphology
b) Cause

Answer 11

a) Biphasic or triphasic, initial -ve deflection, consistent morphology over time. Large amplitude (depends on motor unit density).
b) depolarization of an entire motor unit triggered by voluntary movements

Slide 45

Question 12

Name the 2 MUAP patterns expected in healthy muscles with increasing muscle contraction strenght

Answer 12

• Recruitment pattern: successive activation of additional motor units with increasing strength of voluntary muscle contractions
• Interference pattern: overlap of multiple MUAPs which precludes individual MUAP recognition at MAX contraction

Question 13

Expected MUAP responses at MAX muscle contration for…
a) Healthy muscles
b) Neuropathy
c) Myopathy

SEE TABLE SLIDE 50

Answer 13

a) Complete interference pattern
b) Incomplete interference pattern
c) Lower amplitude (yet complete interference)

Question 14

Fibrillation potentials
1. Morphology
2. Cause
3. Peak ____ days after ____

Answer 14

1. biphasic, ~EPPs but initial deflection is +ve (downward). Sound like fried eggs.
2. AP from a single, denervated myofiber (occ after needle movement)
3. 8 days after denervation (with insertional activity)

Pense au F en italique. Slide 52

Question 15

Positive sharp waves
1. Morphology
2. Cause

Answer 15

1. +ve spike followed by small slow -ve wave. Sound deeper than FPs.
2. AP from single, denervated myofiber (some argue that they are the same as FPs but different needle position relative to AP)

Question 16

Complex repetitive discharges (CRD)
1. Morphology
2. Cause

Answer 16

1. Repetitive, polyphasic, uniform, large amplitude, sound like machine gun
2. GROUP of myofibers firing in synchrony, following CHRONIC denervation. Due to EPHAPTIC spread.

Slide 60

Question 17

Myotonic potentials
1. Morphology
2. Cause

Answer 17

1. Wax-waning amplitude and frequency. Either runs of waves resembling PSWs or FPs. Smaller amplitude than CRD.
2. Repetitive AP from a single myofiber (vs CRD).