Electrodiagnosis can help diagnose Guillain-Barré syndrome (GBS) within the first week, when other tests may be normal. An absent H-reflex combined with abnormal F-waves and upper extremity sensory nerve action potentials, with normal sural nerve responses, suggests early GBS. From days 1-4, an absent H-reflex is most common abnormal finding. By days 5-7, 50-75% of patients show these characteristic electrodiagnostic features. Over time, motor nerve responses become more abnormal with low amplitudes, prolonged distal latencies, and slowed conduction velocities. Outcomes correlate with preserved motor nerve amplitudes—lower amplitudes indicate slower recovery.

1. Electrodiagnosis in GBS
Dr. Munish Kumar
MD, DM Neurology
G B Pant Institute of Medical Education and Research, New Delhi.

2. Electrodiagnosis in GBS
• Diagnosis of GBS within the first week is often difficult
because the elevation of CSF protein and motor/sensory NCS
changes may not evolve until later.
• Yet early diagnosis is desired as treatment may improve the
outcome.

3. EDX in the first week of GBS
• Absent H response, abnormal F wave, and
abnormal upper extremity SNAP combined
with a normal sural SNAP are characteristic of
early GBS.

4. EDX in the first week of GBS
• From day 1 to 4
 Absent H reflex
 Abnormal F Waves (Prolonged / Absent)
 Normal NCS
The H reflex is the only frequently
abnormal finding from the onset of symptoms. The con-
stellation of findings necessary for definite diagnosis was
not commonly seen until the fifth day.

5. EDX in the first week of GBS
• From day 5 to 7
 Absent H reflex (It is reported that the H-reflex was absent in
97% of GBS patients within the first week)
 Abnormal F Waves (Prolonged / Absent)
 SNAP response abnormal in upper limb (Median and Ulnar
sensory potentials are reduced or absent whereas sural sensory
response is normal- sural sparing).
Seen in approximately 50 -75 % of patients
 Motor response : Low amplitude, Prolonged distal latency,
Slow velocity, Temporal dispersion.

6. EDX in the first week of GBS
• Prolonged distal latencies and temporal
dispersion are more commonly demonstrated
than are slow motor conduction velocities and
conduction block.

7. After 1 week
• Motor response becomes more conspicuous.
Low amplitude, Prolonged distal latency, Slow
velocity and Temporal dispersion.

8. Electromyography (EMG)
• Electromyography (EMG) has a secondary role in evaluating patients with AIDP.
• Decreased motor unit action potential (MUAP) recruitment, without evidence of
configuration abnormalities or abnormal spontaneous activity is the initial
finding.
• Occasionally, myokymic discharges are observed during the first few weeks of
illness.
• Fibrillation potentials and positive sharp waves appear between 2 and 5 weeks,
consistent with axonal degeneration.
• The early reduction in fibrillation potentials in proximal compared with distal
muscles likely reflects reinnervation from axonal sprouting or regeneration.

9. Electrodiagnostic criteria for AIDP (Albers et al 1989)
Demonstrate at least three of the following in motor nerves
1. Prolong distal latencies (two or more nerves)
DL>115% ULN (for normal CMAP amplitude)
DL>125% ULN (for CMAP amplitude < LLN)
2. CV slowing (two or more nerves)
CV<90 % LLN (for CMAP amplitude > 50% LLN)
CV<80 % LLN (for CMAP amplitude < 50% LLN)
3. Prolong F response (one or more nerves)
> 125 % ULN (if distal CMAP amplitude is very low , absent F may not
be abnormal)
4. Conduction block / temporal dispersion
Unequivocal Conduction block : proximal/distal CMAP area ratio <0.50
Possible Conduction block : proximal/distal CMAP area ratio <0.70
Temporal dispersion : proximal/distal CMAP duration ratio <0.70

10. Electrodiagnostic criteria (Hadden et al. 1998)
Criteria for AIDP
Conduction velocity <90% LLN
<85% LLN if distal amplitude <50%
LNN
Distal latency >110% ULN
>120% ULN distal amplitude <LLN
Temporal
dispersion
Not considered
Conduction block Proximal-distal amplitude ratio < 0.5
Distal amplitude >20% LLN
F-wave latency >120% ULN
Criteria for AMAN
None of the above except in one nerve if
distal amplitude <10% of LLN
Distal amplitude <80% LLN in two nerves

11. Electrodiagnostic criteria (Feasby et al, 1993)
Acute motor and sensory axonal neuropathy
No evidence of demyelination
Distal CMAP amplitude <80% LLN in at least two nerves
Sensory nerve action potential <50% LLN in at least two nerves

12. Prognosis
• The most powerful predictor of poor outcome is reduced CMAP amplitude to
less than 10% of the lower limit of normal.
• Neurologic recovery is positively and significanty correlated with preserved
mean CMAP amplitude, when the studies are performed between weeks 3
and 5.
• Findings suggestive of predominant demyelination is correlated with
relatively rapid recovery, whereas findings suggestive of severe axonal
destruction are correlated with slow recovery.
• F wave is sensitive for diagnosis of GBS but may not be valuable for
prognosis of GBS.

13. Conclusion
• The H reflex is the most sensitive test for early GBS.
• Absent H response, abnormal F wave, and abnormal
upper extremity SNAP combined with a normal sural
SNAP are characteristic of early GBS.
• If multiple nerves are tested, definite diagnosis is
possible in half the patients, but not until the fifth day
after the onset of symptoms.

14. THANKS…..