seminar on procedure, use of bera in neurology

1. Brainstem Auditory Evoked
Potentials (BAEP)
Dr Bhavin J Patel
SR Neurology
GMC KOTA

2. Introduction
It is electrophysiological responses recorded from ear in
response to auditory stimulation.
Helpful in assessment of functioning of auditory pathway.
First described by Jewett and Williston in 1971

4. Method
Recording electrode:-
 Surface disc or needle
electrode
 Channel 1:- Ai-Cz
 Channel 2:- Ac-Cz
 Ground :- Fz
 Sometimes Ai-Ac channel is used

5. Method
Recording conditions:-
 Analysis time:- 10 ms
 Number of Epoch at least:- 2000
 Stimulation:-
 Stimulus:- brief click of 0.1ms duration, rarefaction
 Click rate 10-30 Hz
 Click intensity:- 60-70 dB SL

6. Waveform
Wave 1:-
 Originates from peripheral portion of
8th nerve
 Normal latency 1.4 ms
 Preserved in CNS abnormality.
Wave 2:-
 Originates from cochlear nucleus or
8th nerve near
brainstem
 Poorly defined in neonates and some
adults
Wave 3:-
 Originates from sup. Olivary nucleus.

7. Waveform
Wave 4 and 5:-
 Wave 4 and 5 originates from lateral
laminiscus and inferior colliculi
respectively.
 Wave 5 in most prominent waveform.
 Latency of wave 5 is 5.5 ms.

8. Variable affecting BAEP
Older patient has longer interepeak latency
Children achieve normal adult value at 18-24 mth of age.
Female have shorter latency
Conductive hearing loss can alter BAEP.
Not affected by drugs.

9. Measurements and normal values
Absolute latencies and amplitude:-
 Absolute latency taken from peak of
the respective wave.
 Amplitudes are measured from peak
to the trough.
 Absolute amplitudes are too variable

10. Measurements and normal values
Interpeak latency:-
1. 1-5 IPL:-
 Latency diff between wave 5 and 1
 Measure of conduction from proximal 8 nerve to Midbrain
 Normal value 4.5 ms.
 Asymmetry of more than 0.5 ms between left and right is
significant.

11. Measurements and normal values
2. 1-3 IPL:-
 Measure of conduction from 8 nerve to lower pons.
 Normal value is 2.5 ms
 More susceptible to tumor,inflammation or other disorder
affecting 8 nrve near cp angle.
3. 3-5 IPL:-
 Measure conduction from lower pons to midbrain.
 Normal value is 2.4 ms.
 Isolated prolongation is not considered abnormal.

12. Measurements and normal
values
4. 5/1 amplitude ratio:-
 Normal value is 50-300%
 Low ratio suggest CNS impairment while high ratio
suggestive of peripheral hearing impairment.

13. Clinical Applications of BAEP
 CP angle tumor:-
 MC- only wave 1 recordable
 Unrecordable waveform
 Prolongation of 1-3 and 1-5 IPL
 Right to left asymmetry in wave 5 latency
 Used for screening and monitoring
 Sensitivity 71%and specificity 74%

14. Clinical Applications of BAEP
 Multiple sclerosis:-
 To detect silent brainstem lesion
 Follow up and monitoring the effect of treatment.
 MC- absence or amplitude reduction of wave 5
 Prolongation of 3-5 and 1-5 IPL
 reduction of 5/1 ratio
 Unilateral abnormality
 High sensitivity in pt with brainstem sign and symptom
 Diagnostic yield is lower than VEP

15. Clinical Applications of BAEP
 Coma and brain death:-
 Normal BAEP in pt with metabolic and toxic
encephalopathy
 Absence of wave 3-5 suggestive of brain death and carries
poor outcome.
 Better in predicting outcome after severe head injury than
GCS, motor signs, pupillary sign and EEG.

16. Clinical Applications of BAEP
 Stroke:-
 Pathological 4 and 5 wave complex suggestive of basilar
artery occlusion distal to AICA.
 Prolonged 1-3 IPL s/o caudal lesion in Pons.
 In Wallenberg syndrome BAEP remains normal.
 Used intraoperative during vertebrobasilar stenting.

17. Clinical Applications of BAEP
In tuberculous meningitis absolute latencies and amplitude
normal but 5/1 wave ratio can be reduced.
In all leuckodystrophies BAEP is consistently abnormal.

18. Newborn Hearing Screening
Approximately 1 of every 1000 children is born deaf.
Automated BAEP has sensitivity of 100% and specificity
of 96-98%.
BAEP should be performed at 3-5 month of age.
Click sensitivity should be 30 dB.
Fetal BAEP can also be done which is identical to neonate.

19. Criteria for screening newborn babies using
BERA
1. Parental concern about hearing levels in their child
2. Family history of hearing loss
3. Pre and post natal infections
4. Low birth weight babies (< 1.5 kg)
5. Hyperbilirubinemia ( billirubin > 20 mg/dl)
6. Cranio facial deformities

20. Criteria for screening newborn babies using
BERA
7. Head injury
8. Persistent otitis media
9. Pyogenic meningitis
10. Cerebral palsy
11. Exposure to ototoxic drugs

21. Limitations
1. All waves are absent in severe hearing loss as well as in
a large acoustic neuroma.
2. A normal BERA response virtually rules out an acoustic
neuroma; but doesn’t at all rule out intrinsic brainstem
lesion or even non-acoustic tumor of the CP angle e.g.
Meningioma.

22. Thank you