Sensory NCS normal values

Question 1

What are filter and screen settings for sensory studies?

Answer 1

low freq (high pass) filter is 2-10Hz
high freq (low pass) filter is 2Khz
gain 20 microvolts/div
sweep is 1 ms/div

Question 2

What happens to SNAP when you raise the low freq filter.

Answer 2

you filter out slower conducting axons which decreased the amplitude
also peak latencies will occur sooner as the SNAP is composed of faster conducting fibers.
onset latency should be unaffected

Question 3

what happens to SNAP when you lower the high freq filter

Answer 3

you filter out faster conducting axons which will prolong the onset and peak latencies
amp mildly reduced.

Question 4

Median to D2 or D3

Answer 4

S2 (palm, 7cm) 
ULN onset lat 1.8
ULN peak lat 2.4
S1 (wrist, 14cm) 
ULN onset 3.2 
ULN peak 4.0

Question 5

Ulnar to D5

Answer 5

S2 (palm, 7cm) 
ULN onset lat 1.8
ULN peak 2.5
S1 (wrist, 14cm)
ULN onset lat 3.1
ULN peak lat 4.0

Question 6

DUC

Answer 6

stim 10 cm proximal to active electrode
ULN onset lat 2.3
ULN peak lat 2.9
Amp >=5 microvolts

Question 7

Radial over EPL tendon

Answer 7

stim 10 cm proximal
ULN onset lat 2.2
ULN peak lat is 2.8
LLN amp is 11microvolts

Question 8

Medial antebrachial cutaneous

Answer 8

stim 10 cm proximal to active recording
ULN onset lat 2.0
ULN peak lat 2.6
Amp LLN 3microvolts

Question 9

Lateral antebrachial cutaneous

Answer 9

stim lateral to biceps tendon recording 10 cm distally on lateral forearm inline with radial styloid.
ULN onset lat 2.1
ULN peak lat 2.5
LLN amp 6 microvolts

Question 10

Posterior antebrachial cutaneous

Answer 10

stim lateral to epicondyle between biceps and triceps.
active record 12 cm distal over mid posterior forearm.
onset latency 1.8-2.6 ms
peak latency 2.0-2.9 ms
peak-peak amp range 3-13 microvolts

Question 11

D1 comparison

Answer 11

stim 10 cm proximal to active recording.
onset latency:
Median >= 11 microvolts
Radial >= 4 microvolts
ULN difference between median and radial peak latency in same limb is 0.6 ms where median has longer latency and 0.4 ms where radial has longer latency

Question 12

Tanscarpal Median/Ulnar mixed

Answer 12

8 cm stim-recording
Peak latencies should be <= 2.4 ms
ULN for peak latency of one nerve vs the other is 0.3 ms

Question 13

D4 comparison

Answer 13

14 cm
ULN peak latency
Median <=3.9 ms
ULN for peak latency difference is 0.4 ms incases where the median is prolonged

Question 14

Superficial Peroneal

Answer 14

14 cm
ULN peak latency is 4.2 ms
LLN peak-peak amp is 4 microvolts

Question 15

Sural

Answer 15

14 cm
ULN peak latency is 4.5 ms
LLN peak-peak amp is 4 microvots

Question 16

Saphenous proximal technique

Answer 16

stim between Sartorius and gracillis tendon 1 cm proximal to the level of inferior border of patella.
pt in supine with knee slightly flexed
Active recording is 15cm distally over medial border of tibia
ULN onset latency 2.9ms
Range of peak-peak amp 7-15 microvots.

Question 17

Saphenous routine study

Answer 17

14 cm
ULN peak latency 4.4ms
LLN peak-peak amp is 1-2 microvolts

Question 18

Medial femoral cutaneous

Answer 18

active electrode placed 14 cm distal to the femoral pulse in inguinal area along an imaginary line from the pulse to the patella.
stim lateral to pulse
ULN peak latency 3.3-3.5 ms
onset to peak amp range 3.4-7.9 microvolts

Question 19

Lateral Femoral Cutaneous

Answer 19

active electrode 17-20 cm distal to ASIS along a line to the lateral patella
S1 below inguinal lig over origin of Sartorius
S2 above inguinal lig 1 cm medial to ASIS
ULN for onset latency
S1 2.9 ms
S2 3.6 ms
peak to peak amp
S1 4-11 microvolts
S2 3-10 microvolts

Question 20

Posterior femoral cutaneous

Answer 20

active electrode placed at midline of posterior thigh 6 cm proximal to mid popliteal region
stimulation is 12 cm proximal to Active electrode in line with the ischial tuberosity in the groove between the medial and lateral HS muscles
ULN peak latency is 3.2 ms
Peak-peak amplitude range 4-12 microvolts

Question 21

Tibial mixed N (Medial and lateral plantar branches)

Answer 21

14 cm
ULN peak latency 3.7 ms
Amplitude range peak-peak
Medial 10-30 microvolts
Lateral 8-20 microvolts

Question 22

Blink Reflex

Answer 22

active placed inferior and lateral to pupil over orbicularis ocule
reference over temple or lateral nose
ground over chin or on forehead
stimulate supraorbital nerve at supraorbital notch
latency measured from first deflection from baseline
ULN for RI is 13 ms S-S latency difference <=7 ms