20: Median Neuropathy at the Wrist

Question 1

Which fiber types are particularly sensitive to demyelination in CTS?

Answer 1

1a afferents (muscle sensory fibers)

Question 2

Again, what is normal ratio of distal-to-proximal CMAP amplitude, and the ratio of distal-to-proximal SNAP amplitude for normal median nerves?

Answer 2

Less than 1.2;

Less than 1.6

Question 3

After carpal tunnel release, what should be seen on EDx studies?

Answer 3

1. Median distal motor latencies should improve and return to normal range
2. Median sensory latencies improve and usually return to normal range
3. Median motor amplitudes should improve and return to normal
4. Median sensory amplitudes might or might not improve
5. Sensitive internal comparison studies might not improve

Question 4

What is normal median nerve CSA at wrist? Above what would absolutely be considered abnormal?

Answer 4

Less than 10;

13

Question 5

What sign when evaluating median nerve in longitudinal axis is pathognomonic for ongoing compression?

Answer 5

Notch sign

Question 6

Most common anomaly of the median nerve? Most common muscular anomalies?

Answer 6

Bifid median nerve (can sometimes see trifid);

Finger extension and flexion with intrusion of the FDS or lumbricals