1. Clinical Applications
ABR

3. There are two general uses of the ABR:
1- Threshold estimation for difficult-to-test patients
2- Identification of auditory nerve and brainstem lesions.

4. Threshold detection

5. Indications Difficult – to- test- patients e.g.;
- Neonates and infants
- Unco-operative Children
- Malingering
Mentally-retarded patients
- To confirm results of PTA

6. Procedure - An intensity series usually is conducted.
- Wave V is the landmark.
- It is generally within dB of the behavioral threshold, at least for the higher frequencies
- The latency-intensity function also can be useful in such assessments

7. Retrocochlear lesions

8. Indications Asymmetric SNHL. - Sudden SNHL - Single Sided Deafness.
- Disproportionate speech discrimination.
- Tinnitus of recent origin

9. Precaution:
The presence of a peripheral hearing loss may confound the interpretation of wave forms in precisely those patients for whom the results of the ABR evaluation are most important.

10. For neurological diagnostic purposes, stimuli generally are presented at a sufficiently high intensity to elicit the potentials at or near their shortest latencies.

11. In most laboratories, it is customary to interpret as abnormal peak latencies, interpeak intervals, and amplitude ratios that are beyond 2.5 or 3 standard deviations from the mean of an age-matched control sample from the normal population.

12. Parameters

13. Absence of Waves
Presence of Wave I only is a strong indication of retrocochlear pathology.
Absence of waves prior to V can result from cochlear pathology, advancing age, high physiological noise levels,
An absence of waves following III is a strong indication of pathology affecting the rostral pons and midbrain.

14. Absolute Latencies: Comparing the wave latencies to the range of normal values is the most basic method for evaluating an ABR and yet it is the most vulnerable.

15. Interwave Latency Differences:
It reflects the time necessary for a nerve impulse to travel from one generator site to another (It is called central conduction time)

16. Interaural Latency Differences:
- Applied primarily to absolute Wave V latencies
- Normal variability of the interaural latency difference suggests that it generally should be less than 0.3–0.4 ms.

17. Amplitudes - It is affected by noise and electrode placement.
- An alternative to absolute amplitude measures is the use of relative amplitudes, particularly the ratio between Wave V (or IV/V) and Wave I amplitudes

18. Criteria for Retrocochlear dysfunction

19. 1. Absence of all ABR waves I through V
1. Absence of all ABR waves I through V. unexplained by extreme hearing loss determined by formal audiometric testing.
2. Abnormal prolongation of I-III, III-V. and I-V interpeak intervals.

20. 4. Abnormal diminution of the IV-V/I amplitude ratio.
5. Abnormally increased differences between the two ears (interaural differences) when not explained by unilateral or asymmetric middle and/or ear dysfunction determined by appropriate audiometric tests.

21. The importance of obtaining formal audiometric testing in patients undergoing ABR examination is emphasized by the consideration that the proper application of two of five criteria of ABR abnormality (Nos. 1 and 5) requires knowledge of the patient’s audiogram.

22. Auditory Steady State Response
ASSR

23. What is ASSR??
Auditory Steady State Response (ASSR) is a totally objective auditory evoked potential used for evaluation of hearing ability in patients non-suitable for traditional audiometric testing.

24. Similarities between ASSR and ABR

25. 1- Both deliver an auditory stimulus.
2. Both stimulate the auditory system.
3.Both record bioelectric responses from the auditory system via electrodes.
4.In each protocol, the patient does not have to respond voluntarily.

26. Differences between ASSR and ABR

27. ABR recordings are most often dependent on the examiner subjectively reviewing the response
ASSR uses an objective, sophisticated, statistics-based mathematical detection algorithm to detect and define hearing thresholds.

28. ABR protocols typically use clicks or tone-bursts in one ear at a time.
ASSR can be used binaurally, while evaluating broad bands or four frequencies (500 Hz, 1,000 Hz, 2,000 Hz, and 4,000 Hz) simultaneously.

29. ABR is useful in estimating hearing thresholds essentially from 1,000 Hz to 4,000 Hz,
ASSR offers more spectral information more quickly, more frequency specific

30. ABR can not differentiate between severe and profound hearing loss
ASSR can estimate and differentiate hearing within the severe-to-profound hearing loss ranges..

32. Indications 1- Newborn infants for screenings and follow-up
2- diagnostic assessments of babies
3- Unresponsive and/or comatose patients,
4- Malingering
(ie, workers' compensation, legal matters, insurance claims, etc).

33. How often are we missing it?
If somebody comes in with DKA, head CT is probably not the first thing we would do
4 cases cited under Pubmed