5 Site of Lesion

7/28/2019 5 Site of Lesion

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SITE OF LESION TESTING:

Distinguishing:

Sensory (cochlear) from neural (retro-

cochlear) disorder.

Different sources of conductive disorder


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MEASURES OF SUCCESS:

SENSITIVITY

Percentage of persons with a disorder who

show up on your test as having that disorder.

In this application, % of persons with neuraldisorder that show a neural result on the site

of lesion test.


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MEASURES OF SUCCESS:

SPECIFICITY

percentage of persons without a disorder who

show up on your test as not having that disorder.

In this application, % of persons with a cochleardisorder (or no auditory disorder at all) who

show up on your test as not having any neural

disorder.


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Loudness Recruitment Tests

Based on the changes in loudness

perception that accompany different

auditory disorders.


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Loudness Growth Patterns

0

20

40

60

80

100

120

10 30 50 70

Normal

Cochlear

Retro-cochlear


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Recruitment:

"Abnormal growth of loudness" or,

persistence of normal loudness above

threshold. More common at higherfrequencies.


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Complete: loudness curve meetsnormal line

0

20

40

60

80

100

120

10 dB 30 dB 50 dB 70 dB

Normal

CompleteRecruitm

ent


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Partial: loudness curveapproaches normal line

0

20

40

60

80

100

120

10dB 30 dB 50 dB 70 dB

Normal

Partial

Recruitment


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Hyper- loudness curve crossesabove normal line

0

20

40

60

80

100

120

10dB 30 dB 50 dB 70 dB

Normal

Hyper-

recruitment


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Recruitment is consistent withcochlear damage

from noise

ototoxic substances

aging

and other causes


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Decruitment:

Abnormal impairment of loudness growth

loudness curve actually moves away from

normal line

lack of functioning nerve cells to code

intensity

associated with retro-cochlear (VIIIth n.)

lesions.


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Decruitment

0

20

40

60

80

100

120

10 dB 30 dB 40 dB 50 dB 100

Normal

Decruitment


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The Alternate Binaural Loudness

Balance(ABLB)Test

requires:

- normal hrg in one ear at freq to be used

- difference in between ears > 25 dB


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ABLB

tones pulse alternating between ears 2 or 3

times per judgement.

pt is asked which ear is louder or same

- begin at 20 SL in poorer ear,

- 0 SL in better ear.

- adjust level in better ear 5 dB steps.


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ABLB

- find level where loudness judged equal.

- increase poorer ear by 10 or 20 dB and

repeat adjustments in better ear.


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PLOTTING ABLB RESULTS:

Use the LADDERGRAM

Connect decibel values judged equally loud


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ABLB SUCCESS?

Sensitivity = 51%

Specificity = 88%


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The Alternate Monaural LB(AMLB) Test

tone alternates between 2 frequencies in the

same ear.

judgment and procedure is similar to

ABLB,

but comparing "the high pitch versus the

low pitch.

generally this is harder for people to do.


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Differential IntensityDiscrimination

The Short Increment Sensitivity Index

(SISI)

The High Level SISI


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TheShort Increment SensitivityIndex

detection of brief (200 ms) 1 dB-increments

in a 20 SL tone

20 trials

> 70 % = cochlear damage

< 30 % = other damage or normal


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B. High Level SISI

at 75 dB HL

Results:

> 70 % = normal or cochlear

< 30 % = retrocochlear


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SISI SUCCESS?

Sensitivity = 68%

Specificity = 90%


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Tone Decay:

Loss of audibility for a tone that is on

continuously.

Greater decay is indicative of retrocochlear

problem.

There are different methods:


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Some Tone Decay Tests

Carhart: begin at 0 SL, up in 5 dB steps

until tone is heard for a full minute

Olson-Noffsinger: begin at 20 SL, up until

heard for full minute.


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Tone Decay Results:

Type I: no decay: norm, conduct or cochlear

Type II: heard for longer times as level is

increased: cochlear

Type III: No growth with increasing level:

retrocochlear


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TONE DECAY SUCCESS?

Sensitivity = 75%

Specificity = 91%


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Bekesy Audiometry:

Pt. controls level of tone,

Continuous tone: tone on constantly (C)

Interrupted tone: pulsed on and off (I)

Adaptation should only occur for C, not I


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Bekesy Results:

I: C and I overlap: norm or cond.

II: C below I at freqs of HL: Cochlear

III: I follows loss, C drops to bottom: Retro

IV: C below I by 20-25 dB: Coch or Ret

V: I below C: False hearing loss


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BEKESY AUDIOMETRY

SUCCESS?

Sensitivity = 42%

Specificity = 95%


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Acoustic Reflex/ARD Success?

Sensitivity = 85%

Specificity = 86%


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Auditory Evoked Potentials:

ABR: within 10 ms of click: Brainstem

disorders.

EcochG: Meniere's disease

MLR: Primary auditory cortex: difficult to

pin down.

Late Cognitive Potentials: processing of

sense info


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Auditory Brainstem Response:

Response within 10 ms of stimulus

waves labeled with Roman numerals

Peaks I, III, and V most useful

Latencies are the key measure

Disorders will produce delays


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ABR SUCCESS?

Sensitivity = 97%

Specificity = 88%


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Middle Latency Response

10-80ms

From primary auditory cortex

Highly variable--poor clinical utility

Some correlation to Central Auditory

Processing Disorders


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Late Cognitive Potentials

80-250 ms

Processing of sensory information

From Primary Auditory and Aud.

Association Cortex

Varies with Attention/Subject wakefulness


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P-300

Obtained in oddball task

Not just auditory

Reflects Change in Working Memory--

Aha!

Changes in latency and amplitude with

variety of disorders

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5 Site of Lesion