Chapter 7: Anomalous Innervations

Question 1

Up to what percent drop in ulnar CMAP amplitude between the wrist and below-elbow site is considered normal 2/2 normal temporal dispersion?

Answer 1

Up to 10%

Question 2

What is the most common MGA?

Answer 2

Crossing of median-to-ulnar fibers supplying the FDI

Question 3

What is necessary to prove an MGA to the FDI?

Answer 3

Higher CMAP amplitude with antecubital fossa stimulation more so than wrist stimulation when recording from the FDI and stimulating the median nerve

Question 4

What are two clues to an MGA and concurrent CTS?

Answer 4

1. Positive deflection with median nerve stimulation at the antecubital fossa recording the thenar muscles
2. Fast conduction velocity of the median nerve in the forearm

Question 5

What is a consequence of a proximal lesion of the median nerve and coexistent MGA?

Answer 5

Could see EMG abnormalities in the ulnar-innervated hand muscles (i.e. FDI and ADM);