EMG-NCV

Question 1

Fasciculation Potentials are

(a) Semirhythmic in their firing pattern
(b) Morphologically the same as motor unit potentials
(c) Produced by ephaptic conduction between single muscle fibers
(d) Randomly firing single muscle fibers

Answer 1

B - Morphologically the same as MUAPs

Fasciculation potentials are spontaneously firing motor unit potentials with the same morphologic characteristics as that of a motor unit or polyphasic action potential. They have an irregular firing pattern usually and the site of origin is unclear. Ephaptic conduction between single muscle fibers is thought to be the mechanism for complex repetitive discharges. Single muscle fiber potentials are much smaller and represent units such as a fibrillation potential.

Question 2

Which modification can be used to increase the sensitivity of repetitive testing in neuromuscular junction disorders?

(a) Decrease the muscle temperature below 30°C.
(b) Allow the muscle to be rested for 6 minutes.
(c) Test the most distal muscles in the feet.
(d) Test the muscles after inducing ischemia.

Answer 2

D

In postjunctional disorders, such as myasthenia gravis, the proximal muscles seem to be more affected and it is thought that this difference is due to the increased temperature as one gets closer to the core of the body. The higher temperatures potentiate a reduced safety factor. Hence, the sensitivity of detecting a decrement response is higher with proximal muscle testing. Maximal exercise can help in demonstrating postactivation exhaustion. When repetitive stimulation is normal in both proximal and distal muscles, testing under ischemic conditions can demonstrate a decrement in the responses.