Gbs Eps Am

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Gbs Eps Am

  1. 1. Electrophysiology Of Guillain-Barre Syndrome Dr. Ahsan Moosa Department Of Neurology Sree Chitra Tirunal Institute for Medical Sciences & Technology Trivandrum, Kerala, India
  2. 2. Guillain-Barre Syndrome <ul><li>Popularly known as a demyelinating disorder [AIDP] </li></ul><ul><li>Also has other variants </li></ul><ul><ul><li>A cute motor axonal neuropathy –AMAN </li></ul></ul><ul><ul><li>Acute motor sensory axonal neuropathy-AMSAN </li></ul></ul><ul><ul><li>Miller Fisher syndrome </li></ul></ul><ul><ul><li>Others </li></ul></ul>
  3. 3. Diagnosis <ul><li>Electro-clinical diagnosis </li></ul><ul><li>Well established clinical criteria- Asbury’s </li></ul><ul><li>ENMG study should always be done </li></ul><ul><ul><li>Confirm the diagnosis </li></ul></ul><ul><ul><li>Alternate diagnosis </li></ul></ul><ul><ul><li>Electrophysiological classification </li></ul></ul><ul><ul><li>Prognosticate </li></ul></ul>
  4. 4. Parameters in ENMG <ul><li>Distal latency </li></ul><ul><li>Nerve conduction velocity (NCV) </li></ul><ul><li>CMAP amplitude </li></ul><ul><li>CMAP duration </li></ul><ul><li>F-waves </li></ul><ul><li>Sensory conduction studies </li></ul><ul><li>H-reflex </li></ul><ul><li>Needle EMG </li></ul>
  5. 5. <ul><li>DL- latency from stimulus onset to appearance of CMAP </li></ul><ul><li>Depends on </li></ul><ul><ul><ul><li>NCV of distal segment </li></ul></ul></ul><ul><ul><ul><li>Neuromuscular Jn. And muscle membrane transit time </li></ul></ul></ul><ul><li>Abnormal ? </li></ul><ul><ul><ul><li>> 125 % ULN if CMAP amplitude is normal </li></ul></ul></ul><ul><ul><ul><li>> 150% ULN if CMAP amplitude is < 80% </li></ul></ul></ul>Distal Latency
  6. 6. Nerve Conduction Velocity <ul><li>Slowing of NCV is one of the hallmarks of demyelinating neuropathy </li></ul><ul><li>Normal </li></ul><ul><ul><li>UL > 50 m/s </li></ul></ul><ul><ul><li>LL > 40 m/s </li></ul></ul><ul><li>Abnormal? </li></ul><ul><ul><li><80% of LLN if CMAP >80% of LLN </li></ul></ul><ul><ul><li><70% of LLN if CMAP < 80% of LLN </li></ul></ul>
  7. 7. CMAP Amplitude <ul><li>Amplitude depends on the no. Of “ functioning ” motor axons with “ secure conduction ” </li></ul><ul><li>So, Low amplitude can occur with both demyelination and axonopathy </li></ul><ul><li>Amplitude < 20% of normal  axonopathic if there are no features of demyelination </li></ul>
  8. 8. CMAP Duration <ul><li>Depend on the range of conduction velocities of conducting fibers </li></ul><ul><li>Abnormal ? </li></ul><ul><ul><li>>15% increase in the negative peak duration of the proximal evoked CMAP compared to distal CMAP -called Temporal Dispersion </li></ul></ul><ul><li>CMAP area: Amplitude X duration </li></ul>
  9. 9. Conduction Block <ul><li>Difference of CMAP amplitude between distal and proximal stimulation </li></ul><ul><li>Value ? consensus </li></ul><ul><ul><li>20%, 30%, 50% </li></ul></ul><ul><ul><li>60% for Tibial </li></ul></ul>
  10. 10. Conduction Block <ul><li>Amplitude fall >30% in proximal stimulation compared to distal irrespective of change in the duration [Temporal dispersion] </li></ul><ul><li>Both TD and CB signify the same process-i.e., segmental demyelination </li></ul>
  11. 11. F-waves <ul><li>Antodromic impulse from the motor nerve  proximal nerve  root  AHC  motor nerve  elicits a delayed small action potential called F-wave </li></ul><ul><li>When Distal segment study is normal, abnormal F-wave indicate proximal dysfunction </li></ul><ul><li>Abnormal ? >120% of ULN if amp >20% LLN or in-excitable </li></ul>
  12. 12. Abnormal F-wave
  13. 13. H-reflex <ul><li>Electrophysiological correlate of areflexia </li></ul><ul><li>Monosynaptic spinal reflex </li></ul><ul><ul><li>Sensory N Dorsal Root Synapse Motor root Motor nerve H Reflex </li></ul></ul><ul><li>Abnormal ? </li></ul><ul><ul><li>Absence of H-reflex </li></ul></ul><ul><li>Almost an universal finding in early GBS </li></ul>
  14. 14. <ul><li>Most proximal and most distal segments are affected early </li></ul><ul><li>NC Velocities are often normal early </li></ul><ul><li>Motor NCV slowest-3rd week </li></ul><ul><li>Sensory NCV slowest-4th week </li></ul><ul><li>Change in NCV - often the last to recover </li></ul><ul><ul><li>When patient improves, NCV may paradoxically slow </li></ul></ul>Evolution Of ENMG Features
  15. 15. Electrodiagnostic Criteria (AIDP) 120-150 >150 >120 >120 % >125 >120 F-wav 56% 63% 58% 21% 37% 72% 43 pts 30 - 30 20% 30 30 TD 30 30 30 20% 30 30 CB >125 >150 >110 >125 % >115 >110 DL <80 (70) <70 <90 (85) 80% (70%) <90 (80) <95 (85) CV (Low amp) Italy group Dutchgroup Ho et al Cornblath ( CIDP) Albers & Kelly Albers et al
  16. 16. Criteria For Electrophysiological Classification <ul><li>Primary Demyelinating </li></ul><ul><ul><li>At least 1 of the following in 2 nerves or 2 in 1 nerve if others are of low amplitude/ in-excitable </li></ul></ul><ul><ul><ul><li>MCV <90% LLN (85% if amp. <50% LLN) </li></ul></ul></ul><ul><ul><ul><li>DML >110% ULN (120% if amp. < 20%LLN) </li></ul></ul></ul><ul><ul><ul><li>C.Block 50% fall proximally if CMAP >20% LLN </li></ul></ul></ul><ul><ul><ul><li>F-latency >120% ULN </li></ul></ul></ul>
  17. 17. Classification contd… <ul><li>Primary Axonal [AMAN/AMSAN] </li></ul><ul><ul><li>None of the features of demyelination in any nerve </li></ul></ul><ul><ul><li>Distal CMAP amp <80% LLN in at least 2 nerves </li></ul></ul><ul><li>Inexcitable </li></ul><ul><ul><li>Distal CMAP absent in all nerves </li></ul></ul><ul><ul><li>OR present in only 1 nerve with amp.<10%LLN </li></ul></ul>
  18. 18. Classification contd… <ul><li>Equivocal </li></ul><ul><ul><li>Does not exactly fit criteria for any group </li></ul></ul><ul><li>Follow up studies will help in reclassifying the Inexcitable and Equivocal group into axonal/demyelinating </li></ul><ul><li>[GBS study Group. Ann Neurol 1998] </li></ul>
  19. 19. <ul><li>Early diagnosis is important </li></ul><ul><li>CSF is often normal in early stages </li></ul><ul><li>Gordon & Wilbourn, 2001 </li></ul><ul><ul><li>31 patients studied within 7 days </li></ul></ul><ul><ul><li>H-reflex absent 97% </li></ul></ul><ul><ul><li>Absent or Low amplitude SNAPs in UE-61% </li></ul></ul><ul><ul><li>Abnormal Median & Normal Sural SNAP 48% </li></ul></ul><ul><ul><li>Abnormal F-waves 84% </li></ul></ul>Early GBS ENMG Features
  20. 20. Early GBS contd… <ul><li>Prolonged DL 65% </li></ul><ul><li>Low CMAP amp 71% </li></ul><ul><li>Temporal dispersion 58% </li></ul><ul><li>Conduction Block 13% </li></ul><ul><li>Slowed Motor conduction velocity 52% </li></ul><ul><li>Definitive diagnosis in 55% usually by 5 th day </li></ul><ul><li>[ Gordon et al . Arch Neurol 2001;58:913] </li></ul>
  21. 21. AMNS Responses <ul><li>Median: Wrist-finger </li></ul><ul><li>Sural: Calf-Lat mall </li></ul><ul><li>In GBS most distal and prox. Segments are affected early </li></ul><ul><li>In true sense AMNS is an artifactual finding </li></ul>
  22. 22. Isolated Absent F-waves in GBS <ul><li>Kuwabara et al. studied 62 pts (Japan) </li></ul><ul><ul><li>12 had Isolated F-wave absence </li></ul></ul><ul><ul><li>Follow up conduction revealed 2 patterns </li></ul></ul><ul><ul><ul><li>Rapid restoration of normal F-waves ! Normal parameters in other sites too [ Rapid clinical recovery ] </li></ul></ul></ul><ul><ul><ul><li>Evolution into AMAN!! </li></ul></ul></ul>
  23. 23. Pathophysiology of Isolated Absent F-wave in GBS <ul><li>Demyelinative conduction block in proximal segment </li></ul><ul><li>Acute axonopathy in proximal segment </li></ul><ul><li>Reversible conduction failure at nodes of Raniver (AMAN) </li></ul><ul><li>Impaired excitability </li></ul><ul><li>[Kuwabara JNNP 2000;68:191] </li></ul>
  24. 24. Inexcitable? <ul><li>Nerve may have conducting axons but inexcitable by conventional stimulation </li></ul>
  25. 25. <ul><li>Preferably done in all cases </li></ul><ul><li>Denervation features may occur as early as first week of illness </li></ul><ul><li>Indicate axonopathic process </li></ul>EMG
  26. 27. <ul><li>Sensory </li></ul><ul><ul><li>Axonal loss </li></ul></ul><ul><ul><li>Reduced SNAPs </li></ul></ul><ul><ul><li>Can be completely normal </li></ul></ul><ul><li>Motor: Usually Normal </li></ul><ul><li>F-waves: Prolonged; Dispersed; Absent </li></ul><ul><li>Serial conduction studies- more useful </li></ul>Miller Fisher Syndrome
  27. 28. <ul><li>CMAP amplitude 0-20% LLN -poor outcome </li></ul><ul><li>Other parameters-do not predict </li></ul><ul><li>Recurrent GBS Vs CIDP? </li></ul><ul><ul><li>No electrophysiological features </li></ul></ul><ul><ul><li>Rely more on clinical features </li></ul></ul><ul><ul><li>A documented normal study between relapses may help </li></ul></ul>Prognostic Factors
  28. 29. <ul><li>Electro-clinical diagnosis </li></ul><ul><li>No universally accepted EP criteria </li></ul><ul><li>Majority 56-87% -AIDP </li></ul><ul><li>Early GBS - normal study unlikely with significant deficit </li></ul><ul><li>Axonal GBS diagnosed in the absence of demyelination features </li></ul><ul><li>Low CMAP –only prognostic indicator </li></ul>Conclusion
  29. 30. <ul><li>Thank you </li></ul>

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