Motor NCS Normal values

Question 1

What is normal latency and Amp of Median motor evoked potential?

Answer 1

Motor recorded over APB, stimulated 8 cm proximal.
ULN for DML 4.2
LLN for amp 4.1mV
(Buschbacher)

Question 2

What is normal latency and Amp of Ulnar motor evoked potential?

Answer 2

Recorded over ADM, stimulated 8 cm proximal,
ULN for DML 3.7
LLN amp 7.9 mV (Buschbacher) (Preston/Shappiro have amp >6 mV)

Question 3

DML and amp of Radial motor?

Answer 3

Recorded over EI, stimulated 4-6 cm proximal,
Avg DML 2.1 ms (buschbacher)
LLN amp2mV (Preston/Shappiro)

Question 4

Minimal F waves

Answer 4

for average height

Median <31ms

Question 5

DML and amp of Tibial N

Answer 5

Recorded over AH, stimulated 8 cm proximal,
ULN for DML is 6.1
LLN for amp is4.4(Buschbacher)

Question 6

DML and amp of Peroneal N

Answer 6

Recorded over EDB, stimulated 8 cm proximal,
ULN for DML is 6.5
LLN for amp is1.3(Buschbacher)

Question 7

What are filter and screen settings with motor NCS?

Answer 7

Low freq filter (high pass) 2-10 Hz
High freq filter (low pass) 10KHz
Sweep speed 2-5 ms/div
Gain 5 mV/div

Question 8

What is normal latency of Tibial H reflex? tests tibial/S1

Answer 8

upper limit of normal from side to side is 2.0ms (buschbacher)
latencies like f waves are based on height and age
30-35ms for h reflexes

Question 9

What is normal latency of Median H reflex? tests median/C6,7

Answer 9

upper limit of normal from side to side is 1.0ms (buschbacher)
upper limit of normal for latency is 18.9 ms (buschbacher)
Mean onset latency is 15.9 (buschbacher)

Question 10

Axillary motor to Deltoid

Answer 10

stimulate at Erb’s point
ULN for DML 5.4
ULN of increased latency from side to side is 0.5 ms.
LLN for amp 4.6

Question 11

Long Thoracic to serratus anterior

Answer 11

Monopolar or concentric needle over digitation of 5th rib at mid axillary line, reference electrode 2 cm caudal, ground electrode over 12th rib at anterior axillary line.
Stimulate at Erb’s point
DML (concentric) <=5.1 ms

Question 12

Musculocutaneous to biceps

Answer 12

stimulate at Erb’s point
ULN for DML 5.6 ms
ULN of increased latency from side to side is 0.4 ms
LLN for amp 4.0 (buschbacher)

Question 13

Suprascapular to supraspinatus and infraspinatus

Answer 13

stimulate at Erb’s point
active recording electrode is 2cm medial to midpoint of spine of scapula for supraspinatus
active recording electrode is 2cm inferior to midpoint of spine of scapula for infraspinatus.
ULN for DML is 4.3 for SS and 4.8 for IS
LLN for amp is 1.5 mV
ULN for s-s increased latency is 0.7 ms (supraspinatus) and 0.4 ms (infraspinatus)

Question 14

What happens if you lower the high frequency filter during a motor study?

Answer 14

you filter out the faster conducting fibers and therefore have increased onset latency.
may have slight decrease in amp

Question 15

What happens if you raise the low frequency filter during a motor study?

Answer 15

you filter out the slower conducting fibers and therefore have decreased amplitude.

Question 16

Femoral to VMO? femoral N/post division of lumbar plexus/L2-4

Answer 16

Gain 1 mV/div
Sweep 2 ms/div
S1 8-10 cm proximal to active recording electrode
S2 below inguinal lig lateral to femoral A
S3 above inguinal lig lateral to femoral A 10 cm proximal to S2
DML >3.7 ms over 14 cm is prolonged (RMUoHP handout)
amp < 500 microV is reduced
NCV < 50 m/s for either S2-S1 or S3-S1 is slow.
do not calculate NCV for S3-S2 (RMUoHP handout)

Question 17

Thoracodorsal N to Latissimus Dorsi?

Answer 17

supine arm abducted to 90 degrees
Stimulate in axilla
Active recording electrode is on posterior axillary line at level of inferior pole of scapula
Reference of ipsilateral flank
DML <= 2.7ms
amp Mean 4.1 mV
ULN decrease in amp s-s is 50%

Question 18

Facial

Answer 18

Buschbacher
Preauricular (anterior to ear) stim latency to nasalis range 2.8-4.1 ms Mean 3.57 ms
Postauricular  stim latency to nasalis range is 3.2-4.4 ms with Mean 3.88 ms

Preston Shapirro
Nasalis amp >=1 mV distal latency <=3.1 ms

Question 19

Spinal Accessory

Answer 19

active recording over UT ~9 cm lateral to SP of C7
Reference 3 cm lateral
Stim posterior triangle of neck 1-2 cm posterior to the posterior border of SCM and slightly above the midpoint
Onset latency range 1.7-3.0ms
Peak to peak amp >3-4 mV