Hearing Loss -A Clinical Approach

Blindness separates us from things

but Deafness separates us

from people -HELEN

KELLER

Johnson jayarajAudiologist &speech pathologist

Hearing loss :Clinical Evaluations and Investigations

PURE TONE AUDIOMETRY

Definition: Pure-tone audiometry is used to determine the threshold of hearing of the patient and is defined as the lowest hearing level at which the patient responds at least 50% of the time to auditory stimuli.

Test Procedure:

Typically, the auditory stimuli are first presented at supra-threshold levels. For each of the techniques, a tone familiarization process is conducted to determine a dB level near the patient’s threshold. From there, the intensity of the stimulus is increased or decreased depending on the patient’s response. If the patient responds to the tone, the intensity of the next tone is decreased in 10 dB steps until the patient ceases to respond. If the patient does not respond to a tone, the intensity of the tone is increased in 5 Db steps until the patient responds. This is known as the “up-5 down-10” technique. This “up-5 down-10” process is repeated until the level at which the patient responds to two out of three presentations or three out of six presentations is determined.

Pure Tone Testing Continued

Bone ConductionProcedure is the same.< indicates right ear.> indicates left ear.

Air conduction indicates amount of

loss.Bone conduction

indicates type of loss.

Air Bone GapIf there is no air bone

gap<15dB, and there is loss, then the loss is

sensorineural.

If there is an air bone gap of

more than 15dB, and bone conduction is normal, it is a

conductive loss.

If there is an air bone gap of more than 15dB and bone

conduction and air conduction both indicate a

loss, the loss is mixed.

How to Read an Audiogram

Terminology Used

Hertz (Hz) is used to describe frequency or pitch, cycles per

second

Decibel (dB) is the unit that describes the intensity, or loudness, of the sound

Audiometric Symbols

Look for the Key on the audiometric Chart Air

Bone

Forehead

Right Left

Normal Audiogram

Determine Degree of LossFrom bass to treble, or low to high pitch

From faint

to intense,

or soft

to loud

STRATERGIES IN HEARING LOSS

VARIOUS TYPES OF HEARING LOSS IN DIFFERENT CLINICAL CONDITIONS

CENTRAL HEARING LOSSCAPD- central auditory processing disorderNEURAL- auditory neuropathy

PERIPHERAL HEARING LOSSCONDUCTIVE SENSORI-NEURALMIXED

Conductive Hearing Loss

Low Frequency Sensori-neural hearing loss

High Frequency Sensori-neural Hearing Loss (Noise Induced)

Mixed Hearing Loss

Masking

RuleApply masking to NTE whenever the AC of the TE exceeds the BC for the NT cochlea by the amount of the minimum IA values.

Minimum IA valuesSupraaural phones = 40 dBInsert phones = 70 dBBone conduction = 0 dB

Masking

Types of masking noise

-WHITE NOISE -NARROW BAND NOISE

Masked Audiometric Symbols

Masked Left Ear Masked Right Ear

The idea behind masking is to keep one ear “busy” while testing the opposite

side

Air

Bone

Audiograms That Indicatea DisorderOtosclerosis -notch at 2KHz ( cookie bite or carhart notch) Presbyacusis-sloping high frequency hearing lossTreacher Collins

Rubella - U Shaped audiogram

Noise-Induced Hearing Loss - audiogram with notch at 4KHz.

Trough shaped or cookie-bite

Noise-Induced Hearing Loss

Tent type of audiogram

Audiogram: Presbycusis

Audiograms that indicate presbycusis show a sharp drop off in the frequencies above 2000Hz

Audiogram in cholesteatoma

CLINICAL CONDITIONS AND TYPES OF HEARING LOSS

ATRESIA- conductive type of hearing lossCERUMENOSIS- conductive type of hearing lossTM PERFORATION- conductive hearing loss , the larger the perforation ,the greater the loss.BAROTRAUMA- M0derate to severe degree with pressure in the ear, nose bleed and middle ear painOTOSCLEROSIS- Causes gradual conductive hearing loss progressing from the low frequencies, to the high frequencies, and then to the middle frequencies. Can begin unilaterally and progress to a bilateral loss.OTITIS MEDIA- ear fullness with conductive hearing loss.ALPORT SYNDROME- mild to moderate degree of sensori-neural hearing loss progressive in nature

CLINICAL CONDITIONS AND TYPES OF HEARING LOSS cont..

Down Syndrome- 60-80% of downs Syndrome experience hearing lossWith conductive or mixed type of hearing loss.

Waardenburg Syndrome – unilateral or bilateral sensori neural hearing loss.

Usher Syndrome- Hearing loss can be congenital (severe to profound) or progressive.

Treacher Collins- Hearing loss is conductive or mixed.

Toxoplasmosis- Causes congenital sensorineural loss that is mild-profound.Rubella- Causes a u-shaped or trough shaped hearing loss.Congenital Cytomegalovirus (CMV)- Causes vision loss, progressive sensorineural hearing loss, and mental retardationHerpes Simplex- sensori-neural hearing loss.

SPEECH AUDIOMETRY

Determines how well a person hears and understands Determines how well a person hears and understands speechspeech..

Spondee wordsSpondee wordsPhonetically balanced monosyllablesPhonetically balanced monosyllables

SRTSRTSDSSDS

SRT should be in close correlation with PTASRT should be in close correlation with PTA..SDS should help in differential diagnosisSDS should help in differential diagnosis

Frequencies and intensities of speech and noise

THE “SPEECH BANANA”

Auditory Milestones

Age

(in months)

Description

0 - 3-startles at a loud sound or noise-stops moving or crying when you

call

3 - 6 turns head or move eyes to a familiar sound

6 - 10 responds to his/her own voice

Auditory Milestones

Age

(in months)

Description

10 - 15-Repeats simple words and sounds you make

15 - 18 Understand simple phrases and can point to body parts

18 - 24 should have at least 150 spoken vocabulary

SPEECH RECEPTION THRESHOLD (SRT)

Definition:

The Speech Recognition Threshold (SRT) is the lowest hearing level at which a patient can hear and understand two syllable words. It is the lowest level in which the patient can correctly repeat or identify the two syllable words 50% of the time.

Purpose of the Test:

1 .SRTs may be obtained to confirm pure tone results;2 .The SRT may be used as the reference point for setting

appropriate levels at which to administer supra-threshold speech recognition tests;

3 .The SRT may be used to determine hearing sensitivity for young children and others who are difficult to test; and

4 .The SRT may be useful in the assessment of patients suspected of pseudohypacusis.

SPEECH RECEPTION THRESHOLD (SRT) CONT..

Phonetically balanced spondee words are given such as : e.g. : armchair

, hardware, whitewash, eardrum.

INTERPRETATION: Once the SRT is obtained, it is compared to the best pure tone average (PTA) for the respective ear, should be within 15dB of the PTA. If not suspect PTA results.

LIMITATIONS OF TEST: The spondees are not representative of the speech that the patient uses when communicating on a daily basis.

SRT be used as part of the diagnostic test battery and not as a stand-alone test.

Hall and Mueller (1997) suggest “spondees aren’t a good reference for determining a level for presentation of word recognition test material, (i.e., sensation level) because the

two tests utilize different stimuli. ”

WORD RECOGNITION TEST

Definition:

The word recognition score (WRS) is the percentage of words correctly identified at some specified level above threshold. The WRS is also known as “the speech recognition score”,

“the speech discrimination score.”

Purpose of the Test:

1 .To provide an estimate of the patient’s ability to recognize single words at suprathreshold levels;

2 .To describe the extent of the hearing impairment in terms of how it affects speech understanding; and

3 .To assist in the differential diagnosis of auditory disorders.

WORD RECOGNITION TEST CONT..

Monosyllabic words (Phonetically balanced) are presented : e.g.: book, dull, show , when, chair etc..

30-40 db above SRT level.

INTERPRETATION: For patients with normal hearing, the speech recognition score is expected to be above 92% correct.For most patients with a conductive hearing loss, the speech recognition score is typically between 80% and 100%For patients with cochlear hearing loss, the speech recognition score is usually consistent with the degree of hearing loss. The greater the hearing loss, the poorer the score.For patients with lesions beyond the cochlea, the speech recognition score will be poorer than expected for the amount of

hearing loss. Scores will appear to be “abnormally low.”

SPEECH AUDIOMETRY GRAPH

SPECIAL AUDIOLOGICAL TEST BATTERY

-ABLB-SISI

-STAT-TDT

CANDIDACY FOR SPECIAL TESTS

Generally patients with sensori-neural hearing loss are administered special test to differentiate the lesion in the cochlea V/s that which is retro-cochlear.

However, normal hearing or conductive loss can co-exist with a retro-cochlear lesion.

So ,whenever a retro-cochlear pathology is suspected ,like patients presenting subjective loss, tinnitus, or other non auditory symptoms, the special audiological test battery should be administered.

Short increment sensitivity index test (SISI)

Detection of brief (200 ms) 1 dB-increments in a 20db Supra threshold tone (carrier tone) in various frequencies , preferably 1000Hz- 4000Hz ,20 trails with 1-6 db increment, asked to identify the number of 1db increment and multiplied by 5 gives the SISI score .

INTERPRETATION:

>70 = % cochlear damage <30 = % retro cochlear lesion or normal

Sensitivity = 68%Specificity = 90%

Tone Decay test ( TDT )

Loss of audibility for a tone that is on continuously.Greater decay is indicative of retrocochlear problem.

methods:

Carhart: begin at 0 SL, up in 5 dB steps until tone is heard for a full minuteOlson-Noffsinger: begin at 20 SL, up until heard for full minute.

INTERPRETATION: Type I: no decay: norm, conduct or cochlearType II: heard for longer times as level is increased: cochlearType III: No growth with increasing level: retrocochlear

Sensitivity = 75%Specificity = 91%

SUPRA THRESHOLD ADAPTATION TEST (STAT)

110dB Tone is presented to the test ear and 90dB making noise is presented to the non test ear for 60secs.

Interpretation:

Decay present within 60secs but not stop completely – normalDecay present within 60secs and stops completely -- Retro cochlear lesion

Sensitivity – 85%Specificity– 95%

CENTRAL AUDITORY PROCESSING DISORDER

-Auditory centers of brain are affected injury, tumor, hereditary or unknown causes

-CAPD does not necessarily involve( although it may) hearing loss.

-CAPD involves fine components of sound e.g. localization, lateralization, auditory discrimination, auditory

pattern recognitionCAPD TEST batteryCAPD TEST battery: :

- -Staggered Spondaic Word (SSW) testStaggered Spondaic Word (SSW) test - -Phonemic Synthesis (PS) testPhonemic Synthesis (PS) test

- -Speech-in-Noise (SN) testSpeech-in-Noise (SN) test - -Masking Level Difference (MLD) testMasking Level Difference (MLD) test

IMPEDANCE AUDIOMETRY

Principles of impedence audiometryA) An oscillator to produce tone of 220Hz.B) An air pump to increase or decrease air

pressure in the canal.C) Microphone to pick up and measure sound pressure level reflected from the

tympanic membrane

Normal and healthy tympanic membrane

Immittance Tests

A(s)

B

A(d)

A

C

+2000-200-400

Five classifications of results, referred to as Modified Jerger Classification System :

Type A(d), A, A(s), B and C

Pneumatic of otoscopy (Siegelization):

Limited mobility

Types Of Tympanogram

Types Of Tympanogram( interpretation)

Otitis media with effusion

What is an acoustic reflex?

The acoustic reflex is the contraction of the stapedius muscle elicited by the presentation of an acoustically loud sound.

•When either ear is presented with a loud sound, the stapedius muscles on both sides contract.

•Contraction of the stapedius muscle tilts the anterior stapes away from the oval window and stiffens the ossicular chain. This results in increased impedance which is measured as a small decrease in compliance by an ear canal probe.

•The stapedius muscle is innervated by the seventh cranial (facial) nerve (CNVII), therefore in the presence of CNVII paralysis, the stapedius muscle is likely to be affected.

Under what conditions will you measure an acoustic reflex?

An acoustic reflex will most likely be elicited if all of the following conditions are met:

1 .Normal middle ear function2 .Loud enough stimulus to elicit the response

3 .No abnormal adaptation to stimulus

A few contra indicators to reflex testing

•Tinnitus •Outer ear infection •Severe recruitment

•Hyperacusis

Ipsilateral Pathway

Contra lateral Pathway

What is and isn’t a reflex?

Acoustic Reflex Patterns


Acoustic reflexes will be absent when a probe is placed in an ear with a middle ear disorder. This is due to the fact that middle ear disorders typically prevent the probe from measuring a change in compliance when the stapedius muscle contracts.

Reflexes will therefore be absent even in the case of a mild conductive hearing loss.

In the presence of a Type C tympanogram, depending on the degree of negative pressure in the middle ear, reflexes can be either present or absent

If acoustic reflexes are present in the probe ear, it is unlikely that a conductive hearing loss exists, except in the rare case of Superior Semicircular Canal Dehiscence (SSCD)



Cochlear Hearing Loss

In ears with a cochlear hearing loss, it is possible for the acoustic reflex to be elicited at sensation levels (SL) of less than 60dB .

The SL is the difference between the ART and the hearing threshold. For example, if the hearing threshold at 1kHz is 50dBHL and the ART is 90dBHL, the sensation level is 40dBSL.

When the SL is less than 60dB, a positive Metz test is indicated. This indicates a cochlear site of lesion (sensorineural loss) due to the loudness recruitment phenomenon.



Retro cochlear Hearing loss

ARTs in ears with retro cochlear (CNVIII) pathology are usually elevated above what they would have been for normal hearing or a cochlear hearing loss. Often they are absent at maximum stimulus levels. ART results should be analyzed in combination with the patient case history, audiogram, speech and tympanometry findings for differential diagnosisThings to note:

•Ears with retrocochlear pathology and normal hearing do not have reflexes 30% of the time

•With a mild 30dB hearing loss, the likelihood of absent reflexes increases.

•The absence of reflexes at 0.5, 1 & 2kHz in the presence of normal/near normal hearing must be considered suspicious unless proven otherwise.

•The affected ear will show absent acoustic reflexes when a stimulus is presented to it in the case of CNVIII lesions.

Retrocochlear Hearing loss

Retrocochlear Hearing loss

Facial nerve/CNVII involvement

Acoustic reflexes are absent when measured on the affected side in the case of a facial nerve disorder (e.g., probe in the affected ear). This is because the stapedius muscle is innervated by the CNVII.

Often, CNVII disorders are easily recognizable (e.g., facial paralysis in the case of Bell’s Palsy) and measurement of the acoustic reflex is used as a tool to monitor the recovery process in such patients.

Facial nerve/CNVII involvement

Reflex Decay Testing

An acoustic reflex decay test measures whether a reflex contraction is maintained or weakens during continuous stimulation (usually 10 seconds). Testing is usually conducted at 500Hz and 1000Hz, but not above these frequencies as even normal ears can show decay at higher frequencies.

Reflex decay testing can be useful in detecting/confirming retrocochlear pathology in patients. Generally patients will present with typical retrocochlear indicators (unilateral tinnitus, asymmetrical hearing loss, dizziness/vertigo)

The test is performed by presenting a continuous stimulus 10dB above the ART for that frequency for a period of 10 seconds. Either the magnitude of the reflex response will stay the same or decrease over the 10 second period. What you are looking for is whether or not the response decays to half its original magnitude. Therefore if the reflex response decreases to 50% of its original magnitude within the 10 seconds of testing, the test would be positive for reflex decay

Reflex Decay Testing

Thank You

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Hearing Loss -A Clinical Approach