Gbs Eps Am

Electrophysiology Of Guillain-Barre Syndrome Dr. Ahsan Moosa Department Of Neurology Sree Chitra Tirunal Institute for Medical Sciences & Technology Trivandrum, Kerala, India

Guillain-Barre Syndrome Popularly known as a demyelinating disorder [AIDP] Also has other variants A cute motor axonal neuropathy –AMAN Acute motor sensory axonal neuropathy-AMSAN Miller Fisher syndrome Others

Diagnosis Electro-clinical diagnosis Well established clinical criteria- Asbury’s ENMG study should always be done Confirm the diagnosis Alternate diagnosis Electrophysiological classification Prognosticate

Parameters in ENMG Distal latency Nerve conduction velocity (NCV) CMAP amplitude CMAP duration F-waves Sensory conduction studies H-reflex Needle EMG

DL- latency from stimulus onset to appearance of CMAP Depends on NCV of distal segment Neuromuscular Jn. And muscle membrane transit time Abnormal ? > 125 % ULN if CMAP amplitude is normal > 150% ULN if CMAP amplitude is < 80% Distal Latency

Nerve Conduction Velocity Slowing of NCV is one of the hallmarks of demyelinating neuropathy Normal UL > 50 m/s LL > 40 m/s Abnormal? <80% of LLN if CMAP >80% of LLN <70% of LLN if CMAP < 80% of LLN

CMAP Amplitude Amplitude depends on the no. Of “ functioning ” motor axons with “ secure conduction ” So, Low amplitude can occur with both demyelination and axonopathy Amplitude < 20% of normal  axonopathic if there are no features of demyelination

CMAP Duration Depend on the range of conduction velocities of conducting fibers Abnormal ? >15% increase in the negative peak duration of the proximal evoked CMAP compared to distal CMAP -called Temporal Dispersion CMAP area: Amplitude X duration

Conduction Block Difference of CMAP amplitude between distal and proximal stimulation Value ? consensus 20%, 30%, 50% 60% for Tibial

Conduction Block Amplitude fall >30% in proximal stimulation compared to distal irrespective of change in the duration [Temporal dispersion] Both TD and CB signify the same process-i.e., segmental demyelination

F-waves Antodromic impulse from the motor nerve  proximal nerve  root  AHC  motor nerve  elicits a delayed small action potential called F-wave When Distal segment study is normal, abnormal F-wave indicate proximal dysfunction Abnormal ? >120% of ULN if amp >20% LLN or in-excitable

H-reflex Electrophysiological correlate of areflexia Monosynaptic spinal reflex Sensory N Dorsal Root Synapse Motor root Motor nerve H Reflex Abnormal ? Absence of H-reflex Almost an universal finding in early GBS

Most proximal and most distal segments are affected early NC Velocities are often normal early Motor NCV slowest-3rd week Sensory NCV slowest-4th week Change in NCV - often the last to recover When patient improves, NCV may paradoxically slow Evolution Of ENMG Features

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

Criteria For Electrophysiological Classification Primary Demyelinating At least 1 of the following in 2 nerves or 2 in 1 nerve if others are of low amplitude/ in-excitable MCV <90% LLN (85% if amp. <50% LLN) DML >110% ULN (120% if amp. < 20%LLN) C.Block 50% fall proximally if CMAP >20% LLN F-latency >120% ULN

Classification contd… Primary Axonal [AMAN/AMSAN] None of the features of demyelination in any nerve Distal CMAP amp <80% LLN in at least 2 nerves Inexcitable Distal CMAP absent in all nerves OR present in only 1 nerve with amp.<10%LLN

Classification contd… Equivocal Does not exactly fit criteria for any group Follow up studies will help in reclassifying the Inexcitable and Equivocal group into axonal/demyelinating [GBS study Group. Ann Neurol 1998]

Early diagnosis is important CSF is often normal in early stages Gordon & Wilbourn, 2001 31 patients studied within 7 days H-reflex absent 97% Absent or Low amplitude SNAPs in UE-61% Abnormal Median & Normal Sural SNAP 48% Abnormal F-waves 84% Early GBS ENMG Features

Early GBS contd… Prolonged DL 65% Low CMAP amp 71% Temporal dispersion 58% Conduction Block 13% Slowed Motor conduction velocity 52% Definitive diagnosis in 55% usually by 5 th day [ Gordon et al . Arch Neurol 2001;58:913]

AMNS Responses Median: Wrist-finger Sural: Calf-Lat mall In GBS most distal and prox. Segments are affected early In true sense AMNS is an artifactual finding

Isolated Absent F-waves in GBS Kuwabara et al. studied 62 pts (Japan) 12 had Isolated F-wave absence Follow up conduction revealed 2 patterns Rapid restoration of normal F-waves ! Normal parameters in other sites too [ Rapid clinical recovery ] Evolution into AMAN!!

Pathophysiology of Isolated Absent F-wave in GBS Demyelinative conduction block in proximal segment Acute axonopathy in proximal segment Reversible conduction failure at nodes of Raniver (AMAN) Impaired excitability [Kuwabara JNNP 2000;68:191]

Inexcitable? Nerve may have conducting axons but inexcitable by conventional stimulation

Preferably done in all cases Denervation features may occur as early as first week of illness Indicate axonopathic process EMG

Sensory Axonal loss Reduced SNAPs Can be completely normal Motor: Usually Normal F-waves: Prolonged; Dispersed; Absent Serial conduction studies- more useful Miller Fisher Syndrome

CMAP amplitude 0-20% LLN -poor outcome Other parameters-do not predict Recurrent GBS Vs CIDP? No electrophysiological features Rely more on clinical features A documented normal study between relapses may help Prognostic Factors

Electro-clinical diagnosis No universally accepted EP criteria Majority 56-87% -AIDP Early GBS - normal study unlikely with significant deficit Axonal GBS diagnosed in the absence of demyelination features Low CMAP –only prognostic indicator Conclusion

Gbs Eps Am

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