single fibre EMG, late waves

Question 1

What is a jitter during stimulated single fiber electromyography?​

Answer 1

Definition: mean of consecutive differences in latency in a sequence of 50-100 potentials (for 25 myofibers): measure of the safety factor of neuromuscular transmission​

​Jitter < 5 µs indicates direct myofibers activation: discarded​

Normal peroneus longus muscle 15 µs​

Abnormal if mean of all tested myofibers > 19.3 µs or if > 10% of myofibers > 29.9 µs​

Increased age: increased jitter

Question 2

What is an axonal reflex? Give one example​

Answer 2

Sudden latency change of the potential (increasing stimulus voltage eliminates the longer latency zone)​

Occasionally, axon reflex appears between M and F wave and represents the presence of collateral sprouting in the proximal portion of the nerve. Usually at submaximal stimuli.​

Question 3

In how many antidromically activated neurons are F waves elicited?​

Answer 3

Only 1-5%​

Question 4

What is the maximal F waves amplitude?​

Answer 4

3% of the M wave amplitude (200-300 µV)​

Question 5

F waves are more representative of … motor neurons with … conducting axons

Answer 5

larger
faster

Question 6

What is the formula to calculate proximal F wave latency?​

Answer 6

Lat F (prox) = Lat F (dist) + Lat M (dist) - Lat M (prox)​

Question 6

What is the ulnar nerve expected minimum F wave latency in dogs? In cats?

Answer 6

Dogs: 6.03 + 0.22 x limb length (cm)​

​Cats:​
Carpus: 7.1 ms​
Elbow: 6.2 ms​

Question 7

What is the tibial nerve expected minimum F wave latency in dogs? In cats?​

Answer 7

Dogs: 3.45 + 0.33 x limb length (cm)​

Cats:​
Hock: 8.56 ms​
Stifle: 7.41 ms​

Question 8

What is the F ratio formula? What is the tibial nerve expected value in dogs? In cats?​

Answer 8

F ratio = ((LatF - latM) - 1) / 2latM

Dogs:
Hock: 2
Stiffle: 0.88

Cat
Hock: 1.75
Stiffle: 0.75

Question 9

At supramaximal stimulus, what is the interaction between H reflex and F wave in humans?​

Answer 9

At supramaximal stimulus, H reflex is cancelled and replaced by F wave (in human only) due to collision and refractoriness.​

Question 10

What is the formula to evaluate H reflex? What are normal values in dogs?​

Answer 10

Formula: thoracic limb length (up to C7) (mm) / H latency (proximal or distal stimulation site) (ms)​

​Normal values:​

Ulnar: 27.5 ± 3.9 m/s (elbow) – 23 ± 2.7 m/s (accessory carpal bone)​

Caudal cutaneous sural nerve mean latency: 20 ± 2 ms​

Ulnar mean latency: 14.1 ± 0.6 ms (elbow) – 16.6 ± 0.8 ms (radiocarpal joint)​

Question 11

Type of stimulation in H-reflex (submaximal, maximal, supramaximal) and anatomic components. ​

Answer 11

Submaximal stimulation​

Afferent – 1A afferent neuron​
Efferent – alpha LMN in ventral gray horn​

Question 12

H waves are

Answer 12

Sensory potentials that synapse on motor neurons

Question 13

Which is the earliest EDX abnormalities in some case of demyelinating diseases?​

Answer 13

Increased F-wave latency​

Because F-wave test a longer pathway than the M-wave alone​