Brachial plexus
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Transcript of Brachial plexus
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Electrophysiology topic
EDX evaluation of brachial plexus-An approach
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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
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Anatomy
• 100,000-160,000 nerve fibers• Intermingle to form various brachial plexus
elements• Roots• Trunks• Divisions• Cords• Terminal nerves
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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
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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
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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
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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
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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
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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
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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)
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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.
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Thank you