Brachial plexus


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seminar on approach to evaluate brachial plexopathy

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Brachial plexus

  1. 1. Electrophysiology topic EDX evaluation of brachial plexus-An approach
  2. 2. 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
  3. 3. Anatomy • 100,000-160,000 nerve fibers • Intermingle to form various brachial plexus elements • Roots • Trunks • Divisions • Cords • Terminal nerves
  4. 4. 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
  5. 5. 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
  6. 6. 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
  7. 7. 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
  8. 8. 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
  9. 9. 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
  10. 10. 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)
  11. 11. 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
  12. 12. 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
  13. 13. 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
  14. 14. 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
  15. 15. 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
  16. 16. 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
  17. 17. 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
  18. 18. 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
  19. 19. 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
  20. 20. 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
  21. 21. 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.
  22. 22. Thank you