EDX evaluation of brachial plexus injury

Electrophysiology topic : 

Electrophysiology topic EDX evaluation of brachial plexus-An approach

Brachial plexus : 

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 : 

Anatomy 100,000-160,000 nerve fibers Intermingle to form various brachial plexus elements Roots Trunks Divisions Cords Terminal nerves

Roots : 

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 : 

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 : 

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 : 

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 : 

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 : 

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 : 

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 : 

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 : 

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 : 

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 : 

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 : 

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 : 

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 : 

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 : 

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 : 

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 : 

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 : 

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.

Slide 33: 

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