Shenoy - Nerve Entrapments

Question 1

Axon loss timeline:

Answer 1

NMJ first, then motor nerve wallerian degeneration (3-7d) then sensory wallerian degeneration (5-10d), then collateral sprouting 3-6 months, which in turn leads to polyphasics and large MUAPs from 6-12 months onwards.

Axon loss = amplitude loss

Question 2

Demyelination and remyelination causes _____ segments + _____ diameter of myelin = decreased ______ despite clinical recovery!

Answer 2

Demyelination and remyelination causes Increased internodal segments + Decreased diameter of myelin = decreased CV despite clinical recovery!

Question 3

Describe the organization of the PNS (epi, peri, endoneurium)

Answer 3

1. Epineurium
   – Resist mechanical forces
   – Vasa nervorum(blood supply)
2. Perineurium
   – Epithelial: around each fascicle
   – Fibrous: between fascicles
   – Homeostasis
   – Blood-nerve barrier
3. Endoneurium
   – Tubular guidance for myelinated axons

Question 4

Timing changes on EMG:

Recruitment
Membrane instability

When for each?

Answer 4

Timing changes on EMG:

• Recruitment changes may be immediate
• Membrane instability only distal to lesion – proximal muscles 10-14 days

– distal muscles 3-4 wks

– Fibs & amplitudes reduce over time

– Reinnervation changes seen in 3-4 months
* ↑MUAP amplitude and duration
* ↑ polyphasics

Question 5

Side to side amplitude > ___% is significant

Answer 5

Side to side amplitude > 50% is significant

Question 6

Conduction block: (AANEM ’99) UL: >__% Amplitude change or __% area LL: >__% Amplitude change or __% area

Answer 6

Conduction block: (AANEM ’99) UL: >30% Amplitude change or 30% area LL: >50% Amplitude change or 40% area

Question 7

Choosing a strategic needle study means:

Answer 7

Proximal & distal site in peripheral nerve involved + associated myotomes

Question 8

Axon grows __/day ~ __/month

Answer 8

Axon grows 1mm/day ~ 1”/month

Question 9

Temperature affects SNAPS more than CMAPS

What other effects does it have?
-Ideal temp for UE and LE
-Change in CV and speed per Celsius
-Change in amp, duration, distal latency

Answer 9

– 32C UE & 30C LL
– 0.2ms /oC or -2.1m/s per /oC for
healthy nerves
– Increased amplitude, distal latency & Duration , decreased CV
– SNAPs more than CMAPs

Question 10

Describe how too low or too high stimulus intensity during NCS can affect findings: (3)

Answer 10

• low = suboptimal amplitude comparison
• Too high = volume conduction
• increase stimulus duration = falsely increased CV

Question 11

IDIOPATHIC FACIAL PARALYSIS

Describe the path of CN 7

Answer 11

CN 7 enters the int. auditory meatus then goes to the petrous portion temporal bone –> Tympanic segment
–> stapedius –> chorda tympani
–> to facial muscles

Question 12

IDIOPATHIC FACIAL PARALYSIS

Entrapment site?

Answer 12

Temporal bone facial canal

Question 13

IDIOPATHIC FACIAL PARALYSIS

Describe the H&P for someone with this condition?

What is it associated with?

Answer 13

 Unilat. Facial weakness (24 -48hrs)

 facial numbness &/or pain

 unilateral hyperacusis (reduced tolerance to sound)

 Tearing and taste changes

 inability to close eye

 associated w/ HSV infection

Question 14

IDIOPATHIC FACIAL PARALYSIS

EDx findings for this condition?

Answer 14

• Facial motor Nasalis, frontalis,
  orbicularis side to side amplitude
  within 10-14 days
• CMAP onset latency & blink reflex
  unclear predictors
• EMG: VMUs in clinically paretic
  muscle indicates incomplete lesion

Question 15

IDIOPATHIC FACIAL PARALYSIS

Tx and Prognosis? (timeline for each)

Answer 15

TX:
* steroids + anti-viral if <72 hrs
* unclear if after 7 days
* eye lubrication
* NCS/EMG within 2 weeks
* Surgical decompression caries many risks

Poor prognosis:
* Severe pain & paresis
* Age>60
* No recovery in 3 wks

Question 16

SPINAL ACCESSORY NERVE INJURY

Anatomy pathway?

Injury site?

Answer 16

• CN11 –> jugular foramen(bulbar)
• C1-5 efferents to SCM & Trapezius.

Injury site: Usually distal to SCM but proximal to trapezius

Question 17

SPINAL ACCESSORY NERVE INJURY

Causes? H&P?

Answer 17

• radical neck dissection
• blunt trauma
• CABG
• ACDF
• CEA

Question 18

SPINAL ACCESSORY NERVE INJURY

Physical Exam findings? Think about your Scapula too!

Answer 18

Physical Exam:
* lateral & inferior scapula at rest
* trapezius weakness w/AROM
shoulder to 90 deg
* lateral and downward rotation of
scapula w/ abduction
* +SCM weakness (cant turn head contralateral)

Question 19

SPINAL ACCESSORY NERVE INJURY

EDx findings?
What leads to poor outcomes?
What treatment options are there?

Answer 19

EDX (not great predictor):
* serial studies to show change, Trapezius CMAP
* EMG trapezius and SCM for membrane instability and VMUs.

Poor outcome if:
* dominant limb,
* scapular winging
* impaired arm elevation

TX: surgical exploration/grafting.

Question 20

SUPRASCAPULAR NERVE

What is the anatomy course of the nerve?

Entrapment sites? (2)

Answer 20

Anatomy:
* C5-6 upper trunk under trapezius
* suprascapular notch
* supraspinatus fossa
* AC and GH joints
* spinoglenoid notch –> infraspinatus

Entrapment sites:
* Suprascapular notch (transverse
scapular ligament)
* spinoglenoid notch (lig)

Question 21

SUPRASCAPULAR NERVE

Common H&P features?

PE Findings? (location of each)

Answer 21

• recalcitrant shoulder pain
• overhead athletes volleyball
• crutch usage
• RTC injuries
• masses/vascular malformations.
• No paresthesias

Question 22

SUPRASCAPULAR NERVE

PE Findings? (location of each)

Answer 22

Physical Exam:
* weak supra & infraspinatus
(suprascapular notch)
* weak infraspinatus
(spinoglenoid notch)

Question 23

SUPRASCAPULAR NERVE

EDx findings and Tx?

Answer 23

EDX:
* NCS UE screen including
SNAPs to r/o plexopathy
* EMG screen, add supra &
infraspinatus w. paraspinals to r/o C5-6 vs. plexopathy.

Treatment:
* Imaging to eval for masses
* surgical referral.

Question 24

AXILLARY NERVE

Nerve course?
Common entrapment sites?

Answer 24

Anatomy:
* C5-6 –> posterior cord –> quadrangular space –> teres minor and deltoid

Entrapment sites:
* Axilla
* Quadrangular space (teres minor/major, medial triceps & humerus) rare.

Question 25

AXILLARY NERVE History and Physical Exam findings

Answer 25

HISTORY: * crutch usage, anterior shoulder dislocation, trauma PHYSICAL EXAM * weak teres minor and deltoid * decreased sensation axillary patch.

Question 26

AXILLARY NERVE EDx, EMG, and Tx?

Answer 26

EDX: * NCS UE: – screen including SNAPs to r/o plexopathy – deltoid CMAP. * EMG – screen – add teres minor and other C5 muscles – paraspinals to r/o C5-6 vs. plexopathy. TX: prognosis is based on etiology of injury.

Question 27

LONG THORACIC NERVE Anatomy course of nerve Entrapment sites?

Answer 27

Anatomy: C5-7 --> thoracic wall --> serratus anterior Injury sites: long course along thorax, subject to traction

Question 28

LONG THORACIC NERVE HPI/Hx? PE findings?

Answer 28

Hx: * direct trauma, fall, wrestling, football, mastectomy, thoracic sx. * * RA can cause Serratus disruption PE: * weak serratus anterior, * resting scapula medial, upward rotation * forward flexion --> medial winging

Question 29

LONG THORACIC NERVE EDx? Tx and Prognosis?

Answer 29

*NCS UE screen including SNAPs to r/o plexopathy *Serial CMPs for more predictive outcome * EMG radiculopathy screen *add serratus (fingers in ICS), can see EKG artifact. * paraspinals to r/o C5-6 radiculopathy vs. plexopathy. Tx: PT strengthening and bracing Prognosis: Idiopathic is better than trauma, 80% vs 50% recovery

Question 30

DORSAL SCAPULAR NERVE Anatomy? Entrapment sites? What Hx is usually seen?

Answer 30

Anatomy: C5 --> Dorsal scapular nerve --> rhomboids & levator scapula Entrapment sites: Scalene medius Hx: * weight lifting * shoulder dislocation

Question 31

DORSAL SCAPULAR NERVE PE presentation?

Answer 31

* +weak serratus anterior,resting scapula lateral, upward rotation * winging is subtle!, overhead elevation decreases winging

Question 32

DORSAL SCAPULAR NERVE EDx findings and Tx?

Answer 32

NCS UE screen including SNAPs to r/o plexopathy, EMG screen, add Rhomboids, and other C5 muscles paraspinals to r/o C5-6 vs plexopathy. Tx requires PT strengthening. Prognosis based on etiology, trauma worse of course

Question 33

MUSCULOCUTANEOUS NERVE Anatomy and course? Don't forget the LAC Injury sites?

Answer 33

* Anatomy: – C5-6 --> uppertrunk --> lat.cord – Coracobrachialis, bicepsbrachii, brachialis --> LAC * Injury sites: – Brachial plexus injuries – axilla – AC fossa

Question 34

MUSCULOCUTANEOUS NERVE Possible etiologies of injury? What other things can look like this that you should rule out?

Answer 34

– anterior dislocation – weightlifting, arm extension, – humerus fracture, – phlebotomy AC fossa Make sure to rule out: – R/O C6 radiculopathy, distal biceps injury.

Question 35

MUSCULOCUTANEOUS NERVE PE findings? EDx findings? Tx?

Answer 35

Weak elbow flexion, with decreased sensation over area of LAC + palpation tenderness over distal biceps tendon. EDx – NCS UE screen including SNAPs to r/o plexopathy, LAC – EMG screen, add other C5-6 muscles, like RTC muscle, peck major. – paraspinals to r/o C5-6 vs plexopathy. Tx Same, PT strengthening and prognosis is based on etiology

Question 36

MEDIAN NERVE List the course of the nerve AND the 4 possible entrapment sites:

Answer 36

C6-T1 --> medial & lateral cords --> median nerve Ligament of Struthers Pronator Teres (syndrome) AIN Nerve entrapment Carpal Tunnel Syndrome

Question 37

Proximal Median nerve Lesion: ligament of struthers Anatomy and location? Incidence? Hx of patient? What distribution? What muscles are affected?

Answer 37

Anatomy – 3-6 cm above elbow – median nerve and brachial artery tacked down @supracondylar process to the medial epicondyle. Incidence 0.5-3%, often bilateral Hx – Possible Vascular symptoms – palmar cutaneous branch & rest median distribution. – ALL MEDIAN muscles weak

Question 38

Proximal Median nerve Lesion: ligament of struthers 3 notable physical exam findings!

Answer 38

cant pronate wrist flexion w/ ulnar deviation ( no median FCR) Active Benediction sign ( can’t close fist, no median FDP)

Question 39

Proximal Median nerve Lesion: ligament of struthers EDx findings and Tx? Think about bracing and surgery options..

Answer 39

EDx: – NCS UE screen – SNAPs to r/o plexopathy, LAC – EMG screen, pronator teres + – FCU negative Tx: – OT : strength, brace to avoid being stuck in extension – prognosis based on etiology of injury – abnormal bony spur - may be detected in X-ray --> Surgical referral

Question 40

Proximal Median nerve Lesion: Pronator teres (PT) Anatomy/course? Hx features? PE findings? Risk factors?

Answer 40

Anatomy: Median nerve runs b/w medial and lateral heads of PT Hx: – pain & tenderness medial forearm – worse w. pronation. – NUMBNESS in median distribution including THENAR area – Easy fatigability – WEAKNESS of APB, flexor forearm – No nocturnal exacerbation PE: – Pronator strength 5/5, check w/ elbow extended. Can worsen pain. – Check FDS arch: resist flexion of flexor superficialis of D3 – Check Lacertus fibrosus (fascial band extending from biceps tendon to forearm fascia) w/ elbow flexed in resisted supination Risk factors: Tight FDS arch, Hypertrophic PTeres, Lacterus fibrosus

Question 41

Proximal Median nerve Lesion: Pronator teres (PT) EDx and EMG findings? Tx?

Answer 41

EDx: – NCS: median SNAP Latency WNL – CMAPs are slow in the forearm segment and MAY show decreased amplitude (axonal) EMG: PT is normal! But distal muscles can show fibs and PSWs (distal membrane instability) Tx: Avoid repeated pronation +/- surgical referral

Question 42

Median nerve : Anterior interossesous nerve (AIN) Anatomy? Common variants/anastomosis? and H&P related to this injury?

Answer 42

Anatomy: It branches off 5-8 cm distal to lateral epicondyle. Innervates the motor for pronator quadratus (PQ), FPL, FDP (d2-3). Also provides sensory to carpal joints but clinically no sensory deficit. Often involved in Martin gruber anastamosis H&P: -Pain & tenderness medial forearm, elbow -Acute onset D1-2 weakness. No Numbness. Weakness of PQ w/ elbow flexed. -Okay sign. Decreased Dexterity

Question 43

Median nerve : Anterior interossesous nerve (AIN) Risk factors? EDx findings? Tx?

Answer 43

Risk factors: – Gantzer’s muscle - anomalous muscle (accessory head of FPL muscle) – palmaris profundus, FCR brevis – trauma – manifestation of neuralgic amyotrophy Edx: – NCS: Screen – PQ needle pickup unreliable – EMG: PQ& FPL+ – Screen for radiculopathy & plexopathy. Tx: – Nsaids, REST – cast in SUPINATION – Surgical referral

Question 44

Explain the Riche-Cannieu anastamosis: -What is the anatomy, incidence? -What EDx clues may indicate it? -When is it significant to be aware of this? -How do you confirm this?

Answer 44

Deep ulnar fibers end up innervating the median nerve hand intrinsic muscles (only Motor). Some studies have said that 55-80% of people may have this! EDx: Median nerve stimulation at the wrist with electrode at APB = low, however stimulation over the ulnar nerve would be normal. The morphology would also look strange EMG: Spontaneous activity at the ABP despite a normal median CMAP and NCS study (indicates the lesion may be from ulnar nerve). Significance: People with severe CTS with this variant will have a normal EMG study of the hand, despite having absent SNAPs of the wrist (ulnar innervation saves the hands) Confirm: comparing motor responses at APB (w/ needle electrode) while stimulating ulnar nerve at the elbow

Question 45

Explain the borders of the carpal tunnel: -Outside -Inside -Carpal bones floor -Ulnar and Radial walls

Answer 45

– Outside: palmaris longus, palmar cutaneous nerve (median) – transverse carpal ligament – Inside: 4 tendons of FDS, 4 tendons of FDP, FPL, Median nerve – Carpal bones: Scaphoid, trapezium, hamate, capitate – Ulnar side: Ulnar Artery & nerve – Radial side: FCR

Question 46

Pathophysiology of Carpal Tunnel Syndrome: -4 common causes What risk factors exist?

Answer 46

Pathophysiology: – – – – -Increased tunnel Pressure -Microvascular compression -Nutrient flow impeded -Ischemia --> demyelination...axonal injury Risk Factors: -- Increased tunnel Pressure: repetitive activity leading to flexor tenosynovitis -- Age , BMI – carpal OA – edema (pregnancy, thyroid) – masses (ganglion, lipoma) – Prolonged vibration – Preexisting (nerve) condition such as DM, radiculopathy, ? Double crush. – ?Handedness LHD > RHD – ? Postures w/ low pressures (typing) – High incidence in poultry workers, construction workers

Question 47

Common Hx of CTS? What should your PE include?

Answer 47

– Middle aged females> males – Paresthesias: D1-3, 4,5 – Worse w/ wrist motion, gripping, hands elevated, night time waking – Relief w/ dependent position or flick (“what do you do when it happens”) – Subjective hand weakness or dexterity loss PE: – Carpal compression (30 sec) – Phalens , tinels – Sensory (filaments?) – motor (LOAF) – Spurlings – atrophy

Question 48

Explain the possible NCS permutations in CTS? What should you check in your NCS exam? Explain the combined sensory index? (3)

Answer 48

– NCS does not correlate to clinical symptoms – may have wnl NCS(small fiber, transient/ischemic What to check: Sensory: median (d2or 3) wrist & mid palm, SNAP amplitudes and latencies Motor: Median distal latency, amplitude, palm for conduction block, Ulnar to eval for neuropathy and martin gruber anastomosis! CSI: Compare Median vs. other nerve at same E1, but diff stim sites. Compare velocity differences! If total > 0.9 = CTS! 1) 2nd lumbrical, Med and Ulnar 8 cm away. - Mixed (normal < 0.3) 2) D4 SNAP, Med and Ulnar 14 cm away. - SNAP (normal < 0.4) 3) D1 SNAP, Med and Radial 10 cm away. - SNAP (normal < 0.5)

Question 49

How should you plan an EMG exam for a CTS patient? Possible findings? Explain mild-mod-severe grading in CTS?

Answer 49

EMG exam should include: – Radiculopathy screen R/O C8-T1, peripheral neuropathy, and APB sampling – Can see membrane instability & occ myokymia -EDx can be normal up to 25% of cases = no surgery Grading: – Mild: prolonged SNAP distal latency ± amplitude – Moderate: abnormal median sensory & motor latencies – Severe : median motor & sensory distal latencies+ absent SNAP or low amplitude CMAP.

Question 50

Treatment options for CTS: OT: Injections: Surgery:

Answer 50

OT: Dorsal or volar in neutral with slight extension. Strengthen the hand instrinsics and focus on tendon gliding to decrease pressure in tunnel. VERY IMPORTANT to address Ergonomics: modify bothersome postures, computer workstation, changing angle of tool usage Injections: steroids +/- lido blind or with U/S for weeks/months of relief Surgery: Same day, 1-2 months rehab. MAY NOT help numbness or current weakness (key is to stop progression).

Question 51

RADIAL NERVE: Describe the nerve's path from root to end Name 4 common entrapment sites

Answer 51

Path: C5-8 --> posterior cord --> axilla --> spiral groove --> BR & ECRL --> PIN & superficial radial. 4 entrapment sites: -Saturday night/honeymooners palsy -PIN syndrome -Radial tunnel syndrome -Chieralgia paresthetica

Question 52

RADIAL NERVE: Spiral Groove Entrapment Anatomy: Typical Hx: PE findings:

Answer 52

* Anatomy: radial nerve --> axilla --> triceps --> spiral groove --> BR&ECRL --> elbow supinator & wrist extensor group. * Hx: -heavy alcohol or sedative binge. -Honeymooner’s: head resting on medial arm -Fx of humerus -Axillary crutches * Physical: – Sparing of triceps – Weak Brachioradialis, Wrist and finger extensors – Numbness in sup. Radial territory

Question 53

RADIAL NERVE: Spiral Groove NCS and EMG findings and where/what to test? Tx?

Answer 53

NCS findings: – NCS: EIP pickup, Stimulation sites below/above elbow, above spiral groove. – Usually demyelinating – sup. Radial SNAP may be normal EMG findings: – deltoid, triceps normal – BR and distal w. decr recruitment , fibs and sharp waves. – Screen for radiculopathy & plexopathy. Tx: – ROM to prevent contractures, E stim. – Dynamic splint ACTIVE FLEXION w/ passive extension – Surgery if no symptomatic improvement in 4 months

Question 54

RADIAL NERVE: PIN Syndrome Anatomy/path: What muscles are spared? Hx of PIN syndrome? Common causes? -Name of injury associated with it? PE findings?

Answer 54

– Radial nerve --> elbow – Superficial radial & Post. Interosseus nerve – --> supinator muscle under arcade of Frohse – SPARES SUPINATOR AND ECRL/B (3)! – Tumor/lipoma, Ganglia, RA/inflammation – Fx of ulna w/dislocation of radial head, MONTEGGIA Fx – Arcade of Frohse: Fibrous/ tendinous band of supinator PE: – Wrist ext and finger ext weakness. – Radial wrist ext deviation(ECRL/B spared) – Thumb ext/abduction (radially) weakness

Question 55

RADIAL NERVE: PIN syndrome Explain the NCS and EMG findings of this injury? Tx?

Answer 55

– NCS: EIP pickup, below/above elbow, above spiral groove. – Slowing across the supinator – sup. Radial SNAP NORMAL – EMG: ALL PIN muscles affected, – SPARING of supinator and ECRL/B Tx; – ROM to prevent contractures, E stim. – Dynamic splinting – Surgery referral if no symptomatic improvement in 4 months

Question 56

RADIAL NERVE: Radial Tunnel Syndrome Explain the course in anatomy: Explain common Hx complaints:

Answer 56

– Radial nerve --> elbow --> between the brachialis and brachioradialis muscles – posterior interosseous nerve enters the supinator muscle Common Hx complaints: – Recalcitrant tennis elbow – Lateral elbow pain in the extensor tendon – Distal to lateral epicondyle – Nighttime pain common

Question 57

RADIAL NERVE: Radial Tunnel Syndrome Explain Physical Exam findings (most important one?): Explain EDx findings and Tx:

Answer 57

PE: – similar to PIN – **Radial wrist ext deviation(ECRL/B spared)** – Tender distal to lateral epicondyle – incr. pain on supination EDx: SAME AS PIN! – NCS: Prolonged latency w/ supination. – sup. Radial SNAP normal – EMG: Need to rule out C7 radiculopathy * TX: Same as PIN