Electrophysiology topic

EDX evaluation of brachial plexus-An approach

Brachial plexus

• One of the most complex and largest PNS structure

• Highly vulnerable

• Extensive non routine NCS

• Time consuming

• Contra lateral asymptomatic limb also needs to be studied

Anatomy

• 100,000-160,000 nerve fibers• Intermingle to form various brachial plexus

elements• Roots• Trunks• Divisions• Cords• Terminal nerves

Roots

• Dorsal and ventral rootlets, dorsal and ventral roots, mixed spinal nerve in inter vertebral foramina, posterior primary rami and anterior primary rami

• Surgeons VS anatomists• C5,C6,C7,C8,T1• Prefixed, Post fixed• Cannot be studied by per cutaneous stimulation• Nerves arising from roots-dorsal scapular, long

thoracic,phrenic

Trunks

• Named after their relationship to one another

• C5-C6 APR-upper trunk• C7-middle trunk• C8-T1-lower trunk• Nerves from proximal upper trunk-

suprascapular, nerve to subclavius• Mid and distal trunks can be stimulated in

supraclavicular fossa and axilla

Divisions and cords

• Each trunk divides into two. lie behind clavicle• Lateral cord-anterior divisions of upper and

middle trunk C5-7roots• Medial cord-continuation of anterior division of

lower trunk C8-T1roots• Posterior cord-posterior division of all trunks C5-

C8 roots• Cord elements can be stimulated

percutaneously

Nerves from cords

• Lateral cord-lateral pectoral, musculo cutaneous, lateral head of median, lateral ante brachial cutaneous.

• Posterior cord-sub scapular, thoraco dorsal, axillary, radial

• Medial cord-medial pectoral, medial ante brachial cutaneous, medial brachial cutaneous, medial head of median nerve, ulnar

• Terminal nerve elements can be studied by percutaneous stimulation

Classification of brachial plexus lesion

• Supra clavicular VS infra clavicular

• Supra clavicular-commoner, severe and worse prognosis

Upper plexus-better, conduction block, proximity to muscles, extra foraminal and repairable

Lower plexus-worse, axon loss, foraminal lesions, distal far muscles

EDX manifestations of pathophysiology

• Axon loss• Demyelinative-conduction block or conduction

slowing

Good prognosis.

stimulation site dependent

distal to lesion –normal NCS

proximal stimulation-axilla and erb’s point

weak muscle, N cmap-EMG shows MUP dropout

Axon loss lesions

• Most common

• Wallerian degeneration 2-3 days later

• Decreased SNAP,CMAP amplitude, norm al distal latencies and conduction velocities

• Needle EMG-fibrillation potentials, MUP drop out (High innervation ratio in limbs)

Severity of lesion

• CMAP amplitudes correlate well with amount of axonal loss in one to one ratio

• Minimal lesion-EMG fibrillations

Normal SNAP,CMAP

• More severe-SNAP amps decrease

• Greater severity-absent SNAP,CMAP amp decreased, MUP dropout

Timing of EDX

• MUP dropout-immediately but severe

• CMAP amps-begin to decrease on day 2-3,reach nadir by day -7

• SNAP amp-begins to drop on day 6 and reach nadir on day 10-11

• Fibrillation potentials-may take10- 21 days to appear

Prognostication

• Re innervation is by collateral sprouting and proximo distal regeneration

• Depends on grade and completeness of injuries, distance between site of injury and innervated muscle

• Regeneration is at 1 inch/month, denervated muscle fibers survive for 18-24 months. so distance more than 2 feet bad prognosis

• Reinnervation normalises CMAP amps but alters morphology and recruitment

prognosis

• No time limit for sensory nerve regeneration

• End organs of sensory nerve fibers donot undergo degeneration

• Reinnervation successful even after two years

• SNAP amplitude decrement correlates well with sensory loss

SNAPs -importance

• Sensory fibers are more sensitive to axon loss than motor fibers. Isolated SNAPs abnormalities do not rule our motor axon involvement

• Intra spinal lesions do not affect sensory conduction. but affect motor NCS and EMG

• Pattern of sensory loss localises lesion to brachial plexus elements much before motor NCS.

• Motor anormalities with normal SNAPs are seen in-myopathies, preganglionic lesions, NMJ, early GBS, study before 6 days

EDX assessment of brachial plexus

• Each brachial plexus element has- Muscle domain/EMG domain SNAP domain CMAP domain

Domains of a distal element is sum of domains of all elements forming it minus domains of elements departing prior to formation of the element

Root domains

• C5 APR- no SNAP domain

CMAP domain-Musc-biceps,

Ax-deltoid

EMG domain-C5 myotome• C6 APR-SNAP domain-LABC(100%),Med-

D1(100%),s-radial(60%),Med-D2(20%),Med-D3(10%)

CMAP domain-Musc-biceps, Ax-deltoid

EMG domain-C6 myotome

Root domains

• C7 APR:SNAP- Med-D2(80%),Med-D3(70%),S-radial(40%)

No dependable CMAP domain EMG-C7 myotome

• C8 APR:SNAP domain uln-D5 CMAP domain: uln-ADM, uln-FDI, Rad- EIP, Med-APB EMG –C8 myotome

• T1 APR:SNAP-MABC CMAP-Med-APB plus C8 cmap

EMG domains

• Upper trunk-(C5 plus C6) minus dorsal scapular, long thoracic nerve.

• Middle trunk-C7 domain minus serratus anterior• Lower trunk-C8 plus T1 APR• Lateral cord-upper and middle trunks minus

supra scapular, subscapular, thoraco dorsal, radial, axillary nerve

• Posterior cord-sum of sub scapular, thoraco dorsal ,axillary and radial

• Medial cord-lower trunk minus posterior division elements

Nerve domains

• Axillary nerve-no SNAP domain CMAP domain: AX-deltoid EMG :innervated muscles• Musculo cutaneous: SNAP-LABC CMAP domain: AX-deltoid EMG-• Radial :SNAP-s radial CMAP: Rad-EDC,nRad-EIP EMG-radial and posterior interossei

Nerve domains

• Median :SNAP domain- Med-D1,Med-D2,Med-D3

CMAP domain-Med-APB

• Ulnar nerve: SNAP domain-Uln-D5

CMAP domain-uln-ADM,

uln-FDI.

Thank you