Brainstem auditory evoked potentials (baep)

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

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

4. 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

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

6. 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.

7. 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.

8. 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

9. Measurements and normal values Interpeak latency:- 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.

10. 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.

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

12. 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%

13. 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

14. 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.

15. 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.

16. 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.

17. 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.

18. 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

19. 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

20. Limitations All waves are absent in severe hearing loss as well as in a large acoustic neuroma. 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.

21. Thank you