Electrodiagnostic Evaluation of Brachial Plexus Injuries

William McKinley MDAssociate Professor PM&R

Virginia Commonwealth University

Incidence

10% of all peripheral nervous system injuries

14% of UE neurological injuriesBimodal distribution:

Obstetrical: male = female, R > L Ages 20-30, males (MVA, violence)

BP lesion localization

Know clinical ANATOMY!!! Root/trunk/division/cord/branch (RTDCB) Motor/sensory innervation

Comprehensive Edx eval NCS & needle EMG Consider less common motor/sensory NCS

BP Anatomy

Anterior (ventral) rami C5-T1R/T/D/C/B (5-3-6-3-5) “Palindrome” BP extends from vert column to axillaclavicle separates R/T from C/B

Supraclavicular (roots & trunks) Infraclavicular (cords & branches)

Cords named in relation to Axillary artery• Lateral (C5,6,7) Posterior (C5-T1) Medial (C8-T1)

Types of Neural Injury

Stretch / traction - most commonContusion - energy dissipationLaceration - fiber disruptionCompression - ischemia / mechanicalIschemia - decreased nutrients

Etiologies

Closed Traction injuries Blunt trauma Radiation Tumor Positioning Brachial Neuritis

Open GSW Laceration Surgical trauma Injection needle

Differential Dx

Proximal mononeuropathies radial, axillary, suprascapular,

musculocutaneous (vs upper / post cord involvement)

Ulnar & median (vs lower trunk / medial cord injury)

Radiculopathy

Neuralgia Amyotrophy

“Brachial plexopathy”, “Parsonage-Turner syndrome” Sx - Acute pain, proximal (upper trunk)

/shoulder innervation involvement SS, long thoracic, axillary often affected Good prognosis

• Recovery (year 1- 35%, year 3 - 90%)

Obstetrical-related

Risk factors: heavy birth weight long, difficult labor breech presentation short maternal stature

Thoracic outlet syndrome (TOS)

Somewhat controversialsx represent vascular vs neurogenic

compromise of: C8 / T1 or lower trunk NCS findings can include abnormalities of

median motor, ulnar sensory & motor

Sports-related injuries

“Burners” or “stingers”Traction of shoulder / head (upper trunk)Sx: paresthesias (rarely weakness)

Neoplastic

Primary tumors - schwannomas, neurofibromas

Secondary tumors (more common) Pancoast tumor (metastatic disease to the upper

lobe of lung) Lower trunk involvement Horners syndrome

Radiation-induced

Related to total dosage & time-dependent > 6000 Rads between 6-24 months

favors upper trunk involvement “myokymia” on needle EMG Ddx: recurrent tumor

Peri-operative / Post-anesthetic

Positioning, straps, traction, pressureUsually upper plexus, good prognosis

Sternotomy (lower trunk / C8-T1)

Needle-induced axillary angiography regional anesthesia

Classifications of BP injuries

Open vs Closed (etiology)Supraclavicular (R/T) vs infraclavicular

(C/B) Supraclavicular is more common

• Preganglionic vs postganglionic

• Upper (Erbs) vs middle vs lower (Klumpke) trunks

Complete vs incomplete

Preganglionic Injury

Nerve root avulsion dorsal & ventral rootlets invested by pia mater / dural funnel

etiology: traction (occasionally missile, knife) Significant traction causes dural rupture / root

vulnerability ventral > dorsal root (esp C8-T1) at higher risk POOR Prognosis!

Edx eval of BP Injury

Nerve Conduction Studies (NCS) common (median, ulnar)

• (evaluates lower trunk & medial cord) less common (radial, MC, Axillary, SS) proximal NCS (C5-6, Erbs point)

• (technically possible, difficult, uncomfortable)

Needle EMG (recruitment, abnl spont pot’s)Late-responses (H-reflex, F wave)- may be

abnormal but ? less useful

Motor/Sensory NCS

Distal latency & NCV are not helpfulAmplitude is “key” parameter

remains NL(on distal stim) if no axonal loss (cond block, demyelination) or with preganglionic BPI (SNAP NL)

look for decreased side-side > 50%• motor day 4-7 (NMJ fragmentation)

• sensory day 8-10

Localizing NCS involement

Terminal branches of Brachial Plexus Median, Ulnar, Radial, Axillary, MC sensory & motor

travel to and from the CNS thru the various roots, trunks, divisions & cords in a fairly consistent “pattern”

Sensory NCS Localization

Nerve Cord Trunk

Musculocut. Lateral Upper

Median (1) Lateral Upper

Median (2-3) Lateral Middle

Radial Posterior Upper

Ulnar Medial Lower

Motor NCS Localization

Nerve Cord Trunk

Musculocutan lateral upperAxillary posterior upper Suprascapular --- upperRadial posterior middle Median medial low Ulnar medial lower

Needle EMG

Abnormal spontaneous potentials positive sharp waves, fibrillations 7-10 days (paraspinal), 2-4 weeks (distal m’s) Important: follow “pattern” of BP innervation

Paraspinal M’s WNL! (distal to Post rami)Decreased recruitment (voluntary MUAP)

Adjunctive tests

Xrays (C-spine, clavicle, humerus, 1st rib)Myelography - w/i 2-3 weeks, nerve root

avulsion forms diverticulum c/w SA spaceMRI (>CT)

Somatosensory Evoked Potential (SSEP)

Supraclav. Fossa / Erbs pt. (N9) / cervical spine (N13) / contra somatosensory cortex (N19)

sensory fibers / post column / thalamus Considerations (less than ideal agreement)

Postganglionic-N9 Abnl (> 30% side-side diff.) Preganglionic- Nl N9 w/ Abnl N13

Axon reflex testing

To evaluate pre vs post ganglionic lesion1% SQ histamine normally leads to a

vasodilation, wheal & flare due to reflex between DRG & cutaneous receptors “Triple response” in light of clinical picture c/w

BPI = lesion proximal to DRG (ie: preganglionic root avulsion & poor prognosis)

Loss of flare = postganglionic (better prognosis)

Case Study

Hx: MVCClinical exam: Prox UE wk (Sh Fl/Abd,

EF), numbness lateral arm/forearm/hand

What NCS & needle exam abnormalities will assist in localizing the site of injury?

Sensory Nerve Localization

Nerve Upper Trunk

Middle Trunk

Lower trunk

Lat cord

Post cord

Med. cord

MC ++ ++

Med(1)

++ ++

Med 3 ++ ++

Radial ++ ++

Ulnar ++ ++

Motor NCS Localization

Nerve Upper trunk

Middle trunk

Lower trunk

Lat cord

Post cord

Median cord

MC ++ ++

Axill ++ ++

SS ++

Radial ++ ++

Median ++ ++

Ulnar ++ ++

Brachial Plexus Injuries (Summary)

Know your ANATOMY!!!

Needle EMG: localizing pattern of involement paraspinal m’s WNL (unless preganglionic)

NCS: localizing pattern of involvement amplitudes often most affected

Have a nice Weekend!!!