EMG/NCS for Upper Extremity PNS Diseases Flashcards
median neuropathy at the wrist
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
anterior interosseous neuropathy
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
median neuropathy at the elbow
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
ulnar neuropathy at the wrist
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)
ulnar neuropathy at the elbow
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
radial neuropathy at the elbow
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
radial neuropathy at the spiral groove
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
radial neuropathy due to improper crutch use
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!)
superficial radial neuropathy
numbness/tingling/burning pain in dorsal hand (thumb, snuffbox region)
NCS:
- Abnormal SNAP to thumb and snuffbox
- Normal CMAP to EIP
EMG:
- normal
posterior interosseous neuropathy
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
axillary neuropathy
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
musculocutaneous neuropathy
weakness of elbow flexion, numbness of lateral forearm
NCS:
- Abnormal SNAP to LAC
- Abnormal CMAP to biceps
EMG:
- Abnormal activity in biceps, brachialis
suprascapular neuropathy
shoulder abduction and/or external rotation weakness
NCS:
- SNAP unavailable
- Abnormal CMAP to supraspinatus
EMG:
- Abnormal activity in supraspinatus and/or infraspinatus
long thoracic neuropathy
medial winged scapula
NCS:
- SNAP unavailable
- Abnormal CMAP to serratus anterior
EMG:
- Abnormal activity in serratus anterior
erb palsy (upper trunk brachial plexopathy)
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
klumpke palsy (lower trunk brachial plexopathy)
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
thoracic outlet syndrome
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)
martin-gruber anastomosis
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
riche-cannieu anastomosis
- 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
