EMG/NCS for Upper Extremity PNS Diseases

Question 1

median neuropathy at the wrist

Answer 1

weakness of thumb abduction/opposition

NCS:
- Abnormal median SNAP to thumb, digit 2, digit 3
- Abnormal median CMAP to APB

EMG:
- Normal vs. decreased recruitment +/- fibs/sharps, polyphasia

Question 2

anterior interosseous neuropathy

Answer 2

weakness of FPL, FDP 2,3, and PQ

NCS:
- Normal median SNAPs and CMAP

EMG:
- Abnormal activity (fibs/sharps), decreased recruitment in FPL, FDP 2,3, and PQ; polyphasia

Question 3

median neuropathy at the elbow

Answer 3

weakness of wrist flexion (FCR), PIP flexion (FDS), thumb flexion (FPL), DIP flexion of digits 2,3 (FDP 2,3), pronation (PQ)

NCS:
- Abnormal median SNAP and CMAP

EMG:
- Decreased recruitment +/- fibs/sharps in every median muscle except PT (if PT syndrome)
- Polyphasia

Question 4

ulnar neuropathy at the wrist

Answer 4

intrinsic hand muscle weakness, paresthesias in digits 4 and 5; weakness in FDI, ADM, finger adduction and abduction, ulnar lumbricals

NCS:
- Abnormal ulnar SNAPs to digits 4 and 5, abnormal CMAP to ADM, FDI
- NORMAL dorsal ulnar cutaneous nerve (DUC) SNAP because the DUC branches off to innervate the skin PROXIMAL TO GUYON’S CANAL

EMG:
- Abnormal activity (decreased recruitment, +/- fibs and sharps) to ulnar hand muscles (ADM, FDI, interossei, lumbricals 3 and 4); polyphasia
- Normal activity in proximal ulnar muscles (FCU, FDP 4, 5)

Question 5

ulnar neuropathy at the elbow

Answer 5

weakness in FDI, ADM, finger adduction and abduction, ulnar lumbricals AND weakness of wrist flexion, DIP flexion of digits 4,5

NCS:
- Abnormal ulnar SNAPs to digits 4 and 5, abnormal CMAP to ADM, FDI
- Abnormal DUC, normal MAC SNAP

EMG:
- Abnormal activity (decreased recruitment, +/- fibs and sharps) to ulnar hand muscles (ADM, FDI, interossei, lumbricals 3 and 4); polyphasia
- Abnormal activity in proximal ulnar muscles (FDP 4,5) (+/- FCU); polyphasia

Question 6

radial neuropathy at the elbow

Answer 6

Weakness of wrist extensors and finger extensors with numbness and tingling in posterior forearm and thumb/snuffbox
- ECRL/ERCB, EIP, ED, ECU
- Elbow flexion may be weak with BR involvement

NCS:
- Abnormal SNAP to thumb and snuffbox
- Abnormal CMAP to EIP

EMG:
- Abnormal activity in all radial muscles except triceps and anconeus

Question 7

radial neuropathy at the spiral groove

Answer 7

Elbow extension is normal (triceps, anconeus)

NCS:
- Abnormal SNAP to thumb and snuffbox
- Abnormal CMAP to EIP

EMG:
- Abnormal activity in all radial muscles except triceps and anconeus

Question 8

radial neuropathy due to improper crutch use

Answer 8

Elbow extension is weak and posterior arm sensation is impaired

NCS:
- Abnormal SNAP to thumb and snuffbox
- Abnormal CMAP to EIP

EMG:
- Abnormal activity in all radial muscles INCLUDING triceps and anconeus
- +/- abnormal activity in axillary-innervated muscles (posterior cord!)

Question 9

superficial radial neuropathy

Answer 9

numbness/tingling/burning pain in dorsal hand (thumb, snuffbox region)

NCS:
- Abnormal SNAP to thumb and snuffbox
- Normal CMAP to EIP

EMG:
- normal

Question 10

posterior interosseous neuropathy

Answer 10

proximal forearm pain with impaired finger extension
(ED, EIP, EPL), wrist extension (ECU) with NORMAL SENSATION

NCS:
- Normal SNAPs to radial, ulnar, median nerves
- Abnormal CMAP to EIP

EMG:
- Abnormal activity in all PIN muscles +/- supinator
- ECRL, ECRB, BR, triceps, anconeus are all spared

Question 11

axillary neuropathy

Answer 11

shoulder abduction and external rotation weakness with impaired sensation over deltoid

NCS:
- SNAP unavailable
- Abnormal CMAP to deltoid

EMG:
- Abnormal activity in deltoid, teres minor

Question 12

musculocutaneous neuropathy

Answer 12

weakness of elbow flexion, numbness of lateral forearm

NCS:
- Abnormal SNAP to LAC
- Abnormal CMAP to biceps

EMG:
- Abnormal activity in biceps, brachialis

Question 13

suprascapular neuropathy

Answer 13

shoulder abduction and/or external rotation weakness

NCS:
- SNAP unavailable
- Abnormal CMAP to supraspinatus

EMG:
- Abnormal activity in supraspinatus and/or infraspinatus

Question 14

long thoracic neuropathy

Answer 14

medial winged scapula

NCS:
- SNAP unavailable
- Abnormal CMAP to serratus anterior

EMG:
- Abnormal activity in serratus anterior

Question 15

erb palsy (upper trunk brachial plexopathy)

Answer 15

Waiter’s tip position: arm is adducted, internally rotated, pronated, wrist flexed
- Weakness of all C5, C6 muscles: deltoid, supraspinatus, infraspinatus, teres minor, biceps, brachialis, brachioradialis, supinator, ECRL, ECRB
- Sensory loss over lateral arm, dorsolateral forearm

NCS:
- abnormal median sensory (C5, C6 fibers), abnormal LAC

EMG:
- abnormal activity and decreased recruitment in the above muscles

Question 16

klumpke palsy (lower trunk brachial plexopathy)

Answer 16

Claw hand (lumbrical weakness), Wartenberg sign, Froment sign, “OK” sign
- Weakness of lumbricals, FDS, FDP, FCU, all intrinsic hand muscles
- Sensory loss of medial arm, medial forearm, and hand

NCS:
- abnormal ulnar SNAP, normal median SNAP

EMG:
- abnormal activity and decreased recruitment in the above muscles

Question 17

thoracic outlet syndrome

Answer 17

NCS:
- abnormal ulnar SNAP/CMAP, abnormal median CMAP (median SNAP is normal), МАС

EMG:
- abnormal spontaneous activity and possibly decreased recruitment of median and ulnar muscles in the hand (lower trunk muscles)

Question 18

martin-gruber anastomosis

Answer 18

In some people, median nerve motor fibers cross over in the forearm to join the ulnar nerve
- Martin-Gruber University → MGU → median-ulnar (anastomosis)
* This means essentially that the median nerve innervates the ADM and FDI in addition to APB etc.
* Ulnar CMAP at the elbow will show a low amplitude when recording over ulnar muscle (e.g. FDI)
* Ulnar CMAP will be “repaired”/normal if you stimulate the ulnar nerve at the wrist
* So, it looks like there is a conduction block between the elbow and the wrist, but there is not
* When you stimulate at the wrist, the median motor fibers have finally joined the ulnar nerve at that point, so you are stimulating all the motor axons that are supplying the ulnar hand muscles When you stimulate proximally at the elbow, you are not stimulating the median fibers that have yet to contribute to the ulnar innervations, thus you only generate part of the full amplitude
* One thing you can do is record over the ADM/FDI, and stimulate the median nerve at the elbow, to see if you generate a sizeable CMAP
- If MGA is present, the CMAP amplitude you generate with this will “add up” with the proximal ulnar CMAP to give you your full CMAP from stimulating the ulnar nerve at the wrist

Question 19

riche-cannieu anastomosis

Answer 19

• Median motor fibers in the hand cross over to join the ulnar nerve
• Essentially now the ulnar nerve gives motor control to the entire hand
• If you record CMAP from APB and stimulate median nerve at the wrist, you will see no CMAP
• If you record CMAP from APB and stimulate ulnar nerve at the wrist, you will see normal CMAP