Shapiro - Technical

Question 1

DDx of high distal and low proximal amplitude

Answer 1

1. Co-stimulation distally.
2. Submaximal stimulation proximally.
3. CB.
4. Pseudoconduction block (early axonal)
5. Anomalous innervation (e.g. MG) Accessory peroneal will have the opposite: distal amplitude lower than proximal

Question 2

• Normal % drop in ulnar CMAP at below elbow compared to wrist stim.
• What would you do if % exceeds normal.

Answer 2

• 10% 2/2 temporal dispersion.
• Confirm there is no submax stim proximally and no co-stim distally.
• Check for MG anastamosis

Question 3

How to check for MG anastamosis. What are the expected findings and how to trouble shoot

Answer 3

MG:
- Stimulation at median nerve at the wrist –> expect to see volume conducted potential w/ downward (positive) deflection.
- Stimulation at median antecubital fossa: small CMAP w/ ampl approx = difference bet prox and distal CMAP.
If a small amplitude is present:
- Make sure it is not co-stim from ulnar at elbow: if you shift stimulater towards the ulnar and the amplitude increases –> it meanse co-stim. If it gets smaller then it is in keeping with MG.
If no CMAP detected:
- Confirm with FDI (most common one)