Current Technique in the Audiologic Evaluation of Infants

1. Current Technique in the Audiologic Evaluation of Infants Todd B. Sauter, M.A., CCC-A Director of Audiology- UMass Memorial Medical Center PhD Candidate – University of Massachusetts Amherst Instructor – Dept. of Otolaryngology University of Massachusetts Medical School

2. Growing Repertoire of Tools at the Disposal of Audiologist • Auditory Brainstem Response (ABR) • Auditory Steady-State Response (ASSR) • Otoacoustic Emissions (OAE) • Multiple Frequency Tympanometry • Middle Ear Muscle Reflexes

3. Questions about Infant Testing by Audiologists (And Others) • Which of these tests are most important? • Which of these tests should come first? • Do I have to do all these tests on every child or just one test?

4. Best Practices in Infant Testing Evidence-Based Clinically Efficient

5. Overview of Tests

6. What is an ABR? • The Auditory Brainstem Response is the representation of electrical activity generated by the eighth cranial nerve and brainstem in response to auditory stimulation

7. How is an ABR recorded? • Electrodes are placed on the scalp and coupled via leads to an amplifier and signal averager. EEG activity from the scalp is recorded while the ear(s) are stimulated via earphones with brief clicks or tones. • A series of waveforms unique to the auditory neural structures is viewed after time-locking the EEG recording to each auditory stimulus and averaging several thousand recordings.

8. Example Normal Hearing 18 Month-Old – 2000 Hz Tone-Burst 70 dBnHL 10 dBnHL

9. Distortion Product Otoacoustic Emissions (DPOAE) Janet Stockard Sullivan 2003

10. What does the presence or absence of OAEs tell us? • Presence = There is no significant conductive loss (no need for bone conduction ABR) and threshold sensitivity is better than ~35 dBHL (except in cases of auditory neuropathy/asynchrony) • Absence = Possible conductive component and/or sensorineural hearing loss ~35 dBHL or greater

11. Tympanometry Janet Stockard Sullivan 2003

12. What does Tympanometry tell us? • If sound energy is being lost in the outer or middle ear due to fluid, vernix, anatomical abnormalities, etc. (conductive component to loss) • Provides cross-check with bone conduction • Had poor sensitivity in the past due to adult settings being used in infant ears (different!). • Now more appropriate equipment settings (1000 Hz probe tone) and normative data for infants is available.

13. Middle Ear Muscle Reflex • Also known as acoustic reflex or stapedial reflex • Measured using same equipment/probe as tympanometry • Looking for sharp reduction in middle ear admittance in response to loud sound due to contraction of middle ear muscles. • Should not be present with conductive loss, severe or profound sensorineural hearing loss, or auditory neuropathy/asynchrony. • Ideally is not used as a stand-alone test, but as a cross-check against ABR, OAE, etc. • Best elicited in infants using a 1000 Hz probe-tone and broadband noise stimulus.

14. What is Auditory Steady-State Response (ASSR)? • Similar to ABR, but EEG activity is analyzed in frequency domain rather than time domain. • Stimulus is modulated pure tone • If response, EEG activity will modulate at same frequency as the stimulus • Statistical computer algorithm determines if response or no response

15. Advantages of ASSR • Can test up to limits of transducer (through severe/profound range) *** Artifactual results? (See Gorga 2004, Small and Stapells 2004) from stimulus artifact or vestibular system • Has potential to be a faster test than ABR when perfected • Some equipment can test multiple frequencies and both ears simultaneously • Uses same basic set-up and equipment as ABR

16. Limitations of ASSR • Cannot analyze raw data, must trust pass/fail criteria given by equipment for each run (can be viewed as advantage) • Extremely limited published clinical database (improving) • Bone conduction not yet perfected for clinical use (Can’t determine conductive vs. sensorineural with ASSR alone) • Large threshold estimation range for normal hearing and mild loss (20 db) • High intensity steady state stimuli may cause acoustic trauma

17. What we still need to learn about ASSR • Conductive vs. Sensorineural loss • Effects of auditory asynchrony, retrocochlear disease, etc. on ASSR • Sedation effects • Are responses at very high levels (>100 dB) truly auditory or artifactual? • Reliable bone conduction testing

18. Gold-Standard: Tone-burst Auditory Brainstem Response OAE ASSR Click ABR Tone-Burst ABR High-Frequency Tympanometry Middle Ear Muscle Reflex

19. Myths about ABR in Infant Threshold Assessment • It’s too slow • It isn’t accurate • It isn’t frequency-specific enough • It is difficult to interpret

20. Myth #1: It’s too slow • Slow stimulus rates (<20/sec) are not necessary in most patients but are still employed by many centers routinely. • The click latency-intensity function is not necessary in most patients and results in too much valuable test time being spent testing above threshold.

21. Rate Effects Above Threshold 11.1/sec 21.1/sec Time for 4000 sweeps – 6 minutes Time for 4000 sweeps – 3 minutes 39.1/sec 55.9/sec Time for 4000 sweeps – 1 minute, 42 sec Time for 4000 sweeps – 1 minute, 10 sec

22. Rate Effects Near Threshold 21.1/sec 39.1/sec 55.9/sec - At low stimulus intensities or near threshold, the early ABR waveforms are absent, while wave V amplitude stays relatively consistent. The use of slow-stimulus rates, in most cases, gains you nothing but longer test times. This is not true in cases of neurological impairment or auditory asynchrony.

23. Myth #2: It Isn’t Accurate • A strict review of tone-burst ABR literature with testing done under appropriate parameters found threshold accuracy of ± 5 dB (95 % Confidence Interval) for 500-4000 Hz. (Stapells 2000) • Poor accuracy is likely most often associated with either poor technique or attempts to interpret poor data

24. Broadband Click ABR – Poorly Used as Estimate of 2000-4000 Hz

25. Broadband Click ABR – Poorly Used as Estimate of 2000-4000 Hz Stapells 1998

26. Myth #3: It isn’t frequency specific enough Stapells 1995

27. Myth #4: It is Difficult to Interpret 50 30 20 - Poor Data - Only Averaged ~ 1000 Sweeps - Difficult to Interpret - Waveforms marked Incorrectly - Clean Data - Averaged 4000+ Sweeps - True Wave Vs are only significant EEG deflection

28. Most Common Mistakes in Infant ABR (IMHO) • Click stimulus used as estimate of 2-4 KHz • Underaveraging of signal • Lack of an consistent test sequence algorithm

29. Sample Test Sequence

30. Testing Sequence for New Infants • Based on answering the most important questions first while the child is asleep: • Is hearing normal at the most important speech intelligibility frequency? • Both ears? • If hearing is not normal, is it a permanent loss? • How severe is it? • Other frequencies? (500-4000 Hz) • If profound loss, is there residual hearing? • Could it be Auditory Neuropathy/Asynchrony? • Will other tests support the diagnosis?

31. Testing Sequence • Is hearing normal at the most important speech intelligibility frequency? - Low intensity (30 dB) 2000 Hz air-conduction tone burst ABR • Both ears? - Get 2000 Hz on each ear before moving on • If hearing is not normal, is it a permanent loss? - Get 2000 Hz bone-conduction information early in the testing to determine if loss is conductive or sensorineural in nature. Not necessary if DPOAEs are present.

32. Testing Sequence • How severe is it? - Use aggressive bracketing technique - search in 30 dB intervals before using smaller (5/10 dB) steps to mark threshold • Other frequencies? - Use a logical sequence of frequencies to get the most useful information first – 2000 Hz, then 500 Hz, then 4000, etc.

33. Testing Sequence • If profound loss, is there residual hearing? - If no tone-burst response, test click ABR at 90 dB and ASSR up to 115 dB (never this high if DPOAE present) • Could it be auditory neuropathy/asynchrony? - Obtain 90 dB slow-rate click ABR at both rarefaction and condensation polarities to look for presence of cochlear microphonic (hair-cell response)

34. Testing Sequence • Will other tests support the diagnosis? - If conductive hearing loss or auditory asynchrony is suspected, cross-check with tympanometry and middle-ear muscle reflexes.

35. Questions? sautert@ummhc.org