repetitive nerve stimulation

Question 1

In pseudofacilitation the change in CMAP is:

Answer 1

An increase in amplitude but not area​

Question 2

A decremential response is defined as ____ or greater decrease in amplitude between the first and ____ CMAP in a train.​

Answer 2

10% and 3rd, 4th or 5th ​

Question 3

Which potentials are compared during supramaximal RNS?​

Answer 3

first potential with either 3rd or 4th, 5th and 10th​

Question 4

In dogs, what is the optimal stimulation rate during RNS?​

Answer 4

In normal dogs, no decremental response > 10% up to 5 Hz​

A stimulation rate of 2-3 Hz is preferable​

Question 5

What is the definition of safety factor during RNS?​

Answer 5

Degree of excess in the number of Ach receptors normally activated in a particular neuromuscular junction (higher in proximal muscle than distal)​

Question 6

What is the definition of pseudofacilitation during RNS?​

Answer 6

Increased synchronization of individual fiber potentials (increased amplitude but decreased area)​

Question 7

How to differentiate Lambert-Eaton myasthenic syndrome and botulism?​

Answer 7

presynaptic blocking of ACH

Electrodiag fiding in both:
Sensory conduction studies are normal.​
CMAP amplitudes are decreased with normal latencies and conduction velocities.​
A decremental response may be seen with slow RNS.​
An incremental response characteristically occurs after fast RNS (30–50 Hz). This finding usually is present in mild or early cases. However, the amount of increment is often not as dramatic as in LEMS, and many times it is lower than 100%.​

in severe botulism, if the amount of ACH release has dropped severely below threshold, even facilitation with rapid RNS may not result in a threshold response, and no increment may occur in the CMAP amplitude.​

Question 8

Give 7 causes of decremental responses in slow RNS

Answer 8

Myasthenia gravis​
Congenital myasthenic syndrome (presynaptic, synaptic, postsynaptic)​
Lambert-Eaton Myasthenic syndrome​

Botulism​

Polymyositis​
Axonopathy​

Drugs (organophosphates)​

Question 9

In case of decrement in slow and fast RNS, how to distinguish polymyositis from myasthenia gravis?

Answer 9

Muscle atrophy in PM​

CK levels​

EMG changes (spontaneous activity, insertion activity)​

CMAP amplitude (decreased in case of PM)

Question 10

Facilitation: is seen in …, indicate ….

Answer 10

Seen in cases of botulism and hypermagnesia​

CMAP and AUC are increased​

Indicates recruitment of more myofibers​

Question 11

What is pause time during RNS? Why is it important?​

Answer 11

Time delay between trains of stimulation​

Ensures enough time is taken to replenish Ach reserves between tests. If lower, higher decrement in normal cases​