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1

What questions do you ask of a patient presenting with hearing loss?

What questions do you ask of a patient presenting with hearing loss?

As with any evaluation, it is important to first obtain a detailed history of the problem. Details such as onset, course since onset, ear(s) involved, excacerbating and relieving factors, and related symptoms are important. Also noted are the presence of tinnitus, vertigo, aural fullness, and ear pain.

A detailed family, medical, and social history, including noise exposure, should be obtained to search for risk factors. Patients also should be asked about temporary or permanent functional changes involving other cranial nerves, in addition to a thorough cranial nerve examination. Recent trauma, either blunt or penetrating, may also produce hearing loss.

2

Describe the two general types of hearing loss. How are they different?

Describe the two general types of hearing loss. How are they different?

  1. Conductive hearing loss (CHL) results from any disruption in the passage of sound from the external ear to the oval window. Anatomically, this pathway includes the ear canal, tympanic membrane, and ossicles. Such a loss may be due to cerumen impaction, tympanic membrane perforation, foreign bodies, otitis media, or otosclerosis. Conductive losses are often correctable with medical or surgical treatment.
  2. Sensorineural hearing loss (SNHL) results from otologic abnormalities beyond the oval window. Such abnormalities may affect the sensory cells of the cochlea or the neural fibers of the eighth cranial nerve. Presbycusis, or hearing loss related to aging, is an example of an SNHL. Eighth cranial nerve tumors may also lead to such a loss. Sensorineural losses are generally permanent and are typically unmanagable medically. Hearing aids usually benefit these patients. Patients may also have a mixed hearing loss that combines both CHL and SNHL (e.g., resulting from chronic otitis media coexistent with cochlear damage).

3

What is the Weber tuning fork test? How is it performed and interpreted?

What is the Weber tuning fork test? How is it performed and interpreted?

The Weber test is not a test of hearing, but it can provide information about the type of loss. In the Weber test a tuning fork is struck and its base is placed midline on the patient’s skull. Commonly a 512 Hz and/or 1024 Hz (hertz or Hz: a unit of measure for cycles/second) tuning fork is used. The patient is first asked where the tone is perceived and next whether the tone is louder in one ear or the other. In CHL, the tone is louder and localizes to the poorer hearing or affected ear. In SNHL, the patient perceives the tone to be louder in the better hearing or unaffected ear. Patients with equal hearing or bilaterally symmetric hearing problems will localize the sound to the skull midline.

4

What is the Rinne tuning fork test? How is it done?

What is the Rinne tuning fork test? How is it done?

The Rinne test is also used to differentiate between CHL and SNHL. The test is performed by alternately placing the prongs of a vibrating tuning fork at the patient’s ear canal and the base of the tuning fork on the patient’s mastoid bone. The patient is asked whether the tone is heard louder at the ear canal or on the mastoid. In the patient with normal hearing and normal middle ear status, the tuning fork is heard louder at the ear canal or equally loud in both positions. Similar findings are expected from a patient with SNHL. Patients with conductive loss, however, hear the tuning fork sound louder at the mastoid position (a negative Rinne test result, bone conduction is greater than air conduction). A negative test is obtained when the CHL is at least 25 decibels hearing level (dB HL).

5

Describe the Schwabach’s tuning fork test.

Describe the Schwabach’s tuning fork test.

The Schwabach’s test is a crude comparison of the patient’s hearing to a presumed normal hearing person (the examiner) and does not replace a complete audiometric evaluation. The base of a vibrating tuning fork is placed on the patient’s mastoid bone. When the tone decays to the point that the patient is unable to perceive it, the examiner quickly transfers the tuning fork to his or her own mastoid. If the examiner is able to hear the tone, the test indicates that the patient has an SNHL. The test result is then reported as “diminished,” reflecting the patient’s hearing status. This test, of course, requires that the examiner have normal hearing.

6

Why are tuning fork tests performed?

Why are tuning fork tests performed?

Tuning fork tests are done to primarily assist in evaluating the possible type of hearing loss (CHL versus SNHL). They contribute little to evaluating the presence or degree of hearing loss, which should be done with a complete audiometric evaluation. However, they can be useful in a situation where the patient would not tolerate complete audiometric testing, (e.g., a trauma patient in the ICU), or if audiometry is not available.

7

How wide is the frequency range for normal hearing?

How wide is the frequency range for normal hearing?

The human ear can detect sound in the frequency range of 20 to 20,000 Hz. However, the typical adult can only detect frequencies between 200 and 10,000 Hz. The speech frequency spectrum ranges from 400 to 5000 Hz, and audiometric test procedures typically evaluate 250 to 8000 Hz.

8

What is a decibel?

What is a decibel?

A decibel is an arbitrary unit of measurement that is logarithmic in nature. Several decibel scales are used to measure sounds and hearing, and it is necessary to identify each reference scale when presenting a value in decibels. For example, hearing is measured on a biologic scale in decibels hearing level (dB HL), whereas environmental sounds are measured on a physical scale in decibels sound pressure level (dB SPL). The normal ear is not equally sensitive to all frequencies, and it is able to hear mid frequencies better than low and high frequencies. Normal hearing at 125 Hz is about 45 dB SPL, at 1000 Hz is about 7 dB SPL, and at 6000 Hz is about 16 dB SPL. A reference level of 0 dB HL represents normal hearing across the entire frequency spectrum.

9

What is an audiogram?

What is an audiogram?

An audiogram is produced using a relative measure of the patient’s hearing as compared with an established “normal” value (Figure 33-2). It is a graphic representation of auditory threshold responses that are obtained from testing a patient’s hearing with pure-tone stimuli (Table 33-1). The parameters of the audiogram are frequency, as measured in cycles per second (Hz), and intensity, as measured in dB HL. The typical audiogram is determined by establishing hearing thresholds for single-frequency sounds at 250, 500, 1000, 2000, 4000, and 8000 Hz; the primary speech thresholds are 500, 1000, and 2000 Hz. The interoctaves of 3000 and 6000 Hz are commonly measured as well.

10

What is normal hearing?

What is normal hearing?

Practically speaking, normal adult hearing is represented as a general range between 0 and 20 dB HL. The measurement of hearing is based on threshold responses, with a threshold defined as that point at which a patient perceives a sound stimulus 50% of the time. Patients with hearing loss have audiograms with poorer thresholds (larger numbers in decibels) at the involved frequencies. This is generally considered to be >20 dB (Table 33-2).

11

What is the pure-tone average?

What is the pure-tone average?

The pure-tone average (PTA) is an estimate of the patient’s ability to hear within the speech frequencies. The value is calculated by averaging the air conduction hearing thresholds at 500, 1000, and 2000 Hz. For individuals with a precipitously sloping hearing loss, a Fletcher’s average is commonly used, which is the average of the two best thresholds that are typically used to obtain the PTA.

12

When an audiologist says that a hearing loss requires masking to verify, what does this mean?

When an audiologist says that a hearing loss requires masking to verify, what does this mean?

Loud sounds presented to the test ear can travel via bone conduction through the skull and be perceived in the opposite, nontest ear. This phenomenon, called crossover, can obscure measurement results in the test ear. Therefore, the nontested ear must be excluded from the test. Air conduction sounds can cross over when a difference of as little as 40 dB exists between the air conduction threshold of the test ear and the bone conduction threshold of the nontest ear. This may vary depending on head size and transducer used. Headphone crossover occurs at lower levels (40 to 60 dB) than insert earphones (70 to 90 dB). Bone conduction sounds may cross over when a difference as little as 0 dB exists between the bone conduction thresholds of the two ears. Masking is the simultaneous presentation of sound to the nontest ear while testing the other ear with the stimulus; this serves to prevent the nontest ear from interfering with true sound perception in the test ear.

13

How does the audiologist distinguish between air and bone conduction deficits?

How does the audiologist distinguish between air and bone conduction deficits?

In measurements of air conduction hearing thresholds, headphones or inserted ear phones deliver sound to the patient. If a hearing loss is noted on testing air conduction, bone conduction hearing thresholds are subsequently performed. Bone conduction is tested by placing a vibrating device (bone oscillator) behind the ear on the mastoid. The bone oscillator presents the sound to the inner ear, thus bypassing the middle ear system. Patients with SNHL have equal hearing thresholds by air and bone conduction measurements. Patients with CHL have normal cochlear function; therefore, they show normal hearing thresholds by bone conduction but poor hearing thresholds by air conduction.

14

What do you look for on an audiogram to tell whether a hearing loss is sensorineural or conductive?

What do you look for on an audiogram to tell whether a hearing loss is sensorineural or conductive?

Look for an air–bone gap. An air–bone gap is the difference in decibels between the hearing thresholds obtained using the insert earphones (air conduction) and those obtained using the bone oscillator (bone conduction). Significant air–bone gaps represent CHL (Figure 33-3). Because the patient hears better through bone conduction than with insert earphones/headphones, a gap exists between the two measurements. With normal hearing, the air and bone conduction thresholds are approximately equal (≤10 dB difference). With SNHL (Figure 33-4), the air and bone conduction thresholds are approximately equal but, overall, show a deficit (>10 dB). A conductive loss would result in a gap between a more normal bone conduction threshold, and the poorer air conduction threshold.

15

What is the speech reception threshold (SRT) test?

What is the speech reception threshold (SRT) test?

This test is performed to confirm the pure-tone threshold findings. The patient is familiarized with a specific set of bisyllablic words, known as spondees, which are then presented to the patient at decreasing intensities. Spondees are two-syllable compound words that are pronounced with equal emphasis on each syllable—for example, oatmeal, popcorn, and shipwreck. The SRT is the lowest intensity at which the patient correctly identifies the word in 50% of the presentations. The SRT should typically be within ±7 dB of the three-frequency pure-tone average or, for patients with a precipitously sloping hearing loss, the Fletcher’s average.

16

Describe the speech discrimination or recognition test.

Describe the speech discrimination or recognition test.

The purpose of the speech discrimination or recognition test in quiet is to assess the patient’s understanding of speech when the loudness level is sufficient for the listener to perform maximally. A standardized list of single-syllable words are presented approximately 40 dB above the SRT or at the patient’s most comfortable loudness level. The patient repeats each word, and the score is determined according to the percentage of words that are correctly identified. Good to excellent understanding is considered to result in scores between 80% to 100%; however, critical difference scores are dependent on the number of items in each list and test method. Recorded stimuli are considered to be the most generalizible between settings and sessions. While 25-word lists are generally the clinical standard, the critical difference scores or the test-reretest reliability can vary as much as 40%, with the most variability expected for poorer scores. Speech recognition can also be assessed with sentences in the presence of varying degrees of background noise. This application is typically used to estimate functional performance with and without hearing aids or cochlear implants.

17

What do you do when the patient’s tuning fork test results do not agree with the audiogram?

What do you do when the patient’s tuning fork test results do not agree with the audiogram?

Consider a number of factors:

  1. Has the audiometry equipment recently been producing questionable results?
  2. Do both headphones work?
  3. Is the examiner properly using the tuning forks?
  4. Is the examiner comfortable with the anatomy?
  5. Does the patient understand the instructions?
  6. Does the patient have a secondary gain?

If available, old audiograms should be obtained for comparison. Most importantly, the inconsistency needs to be resolved.

18

What is the immittance test battery?

What is the immittance test battery?

The immittance test battery is not a hearing test, but rather an electroacoustic testing procedure that is used to evaluate the status of the auditory system. The test battery typically includes tympanometry (a measurement of energy transmision through the middle ear) and ipsilateral and contralateral acoustic reflex measurements.

19

How is the examiner’s subjective evaluation of tympanic membrane mobility quantified objectively?

How is the examiner’s subjective evaluation of tympanic membrane mobility quantified objectively?

Tympanometry can be thought of as electronic pneumatic otoscopy. Tympanometry is an objective test that measures the mobility, or compliance, of the tympanic membrane and the middle ear system. A seal is formed between the instrument probe and the external canal. Air pressure is manipulated into the space bound by the probe, the external ear canal, and the tympanic membrane. Tympanometry results are represented by air pressure/compliance graphs known as tympanograms. The compliance of the tympanic membrane is at its maximum when air pressure on both sides of the eardrum is equal. The peak air pressure of the tympanogram is equal to the patient’s middle ear pressure. The range of normal middle ear pressures is between 0 and −150 mmH2O and represents normal eustachian tube function. Middle ear pressures that are more negative than −150 mmH2O are indicative of poor eustachian tube function.

20

The chart of a patient says that she had a type B tympanogram on her last visit. What does this mean?

The chart of a patient says that she had a type B tympanogram on her last visit. What does this mean?

  • Type A-  Normal middle ear function
  • Type As-  Tympanic membrane is stiffer than normal (lower compliance), in the presence of normal middle ear pressures (i.e. otosclerosis)
  • Type Ad-  Tympanic membrane is more flaccid than normal (higher compliance), in the presence of normal middle ear pressures (i.e. ossicle discontinuity)
  • Type B-  Also known as a flat tympanogram, It shows no peak pressure and indicates nonmobilityof the thmpanic membrane (e.g. middle ear effusion or perforated tympanogram
  • Type C-  Tympanic membrane shows a peak in the negative pressure range  (< -150 mm H2O) ; indicates poor eustacian tube function.

21

How can I tell whether a type B tympanogram results from fluid or a perforation?

How can I tell whether a type B tympanogram results from fluid or a perforation?

Look at the middle ear canal volume, normally recorded next to the tympanogram. This test is conducted with an immittance meter and measures the volume medial to a hermetically sealed probe. The result, typically reported in centimeters cubed (cm3), is the absolute volume of the ear canal when the tympanic membrane is normal. However, in situations where the tympanic membrane is perforated, the measurement is quite large as the volume of the middle ear space is also included. Pressure equalization tubes will also result in a large volume measurements. Normal middle ear volumes for children range from about 0.5 to 1.0 cm3, and normal middle ear volumes for adults are up to about 3 cm3.

22

What is the function of the stapedius muscle?

What is the function of the stapedius muscle?

The stapedius muscle, attached to the posterior crus of the stapes, contracts reflexively at the onset of a loud sound. The muscle contracts bilaterally, even when only one ear is stimulated. The stapedius muscle is thought to provide some protection to the inner ear in the presence of potentially damaging intense sound. The acoustic reflex causes immediate stiffening of the ossicles and increased compliance of the middle ear system and tympanic membrane. Testing the contraction of the stapedius muscle by measuring the compliance change of the tympanic membrane is known as the acoustic reflex, an important part of the immittance test battery.

23

Describe the acoustic reflex neural pathways.

Describe the acoustic reflex neural pathways.

The acoustic reflex has both an ipsilateral and contralateral pathway. The majority of neurons run through the ipsilateral pathway. The ipsilateral pathway begins at the cochlea and proceeds through the eighth nerve, cochlear nucleus, trapezoid body, superior olivary complex, and facial motor nucleus to the ipsilateral stapedial muscle.

The contralateral pathway crosses the brain stem at the superior olivary complex to continue to the opposite cochlear nucleus, trapezoid body, contralateral olivary complex, motor nucleus of the facial nerve, and opposite stapedius muscle.

24

How is the acoustic reflex measured?

How is the acoustic reflex measured?

The acoustic reflex is measured with the immittance meter. The change in compliance of the middle ear is caused by contraction of the stapedial reflex and is time-locked to the presence of a loud acoustic stimulus. The ipsilateral reflex is measured with the stimulus presented through a sealed probe. The contralateral reflex is measured through a probe on the opposite ear of the stimulus. Measurement of the acoustic reflex is a valuable technique that is used to determine the integrity of the neural pathways. It is also used to detect eighth nerve tumors, sensory cell impairment of the cochlea, and loudness intolerance for patients with SNHL.

25

What is auditory brain stem response audiometry?

What is auditory brain stem response audiometry?

Auditory brain stem response (ABR) is an objective, physiologic measurement of auditory neural function. This evoked potential can be useful as an assessment of audiologic or neurologic function. ABR recordings using clicks and frequency-specific tone bursts can be useful in predicting behavioral hearing thresholds in infants or young children, or in adults who cannot or will not give accurate behavioral results. By decreasing the amplitude of the stimulus, the peaks of the waveform will eventually disappear. The presence of neural tumors of the eighth cranial nerve, internal auditory meatus, and cerebellopontine angle often result in abnormal waveforms.

Accurate assessment requires that the patient is either asleep or in a quiet, relaxed state. The test is conducted using scalp electrodes to pick up the minute electroencephalographic activity created when sound travels through the auditory pathway listed below. A series of clicks or tone bursts is delivered to the patient through inserted earphones. When an acoustic signal stimulates the ear, it elicits, or “evokes,” a series of small electrical events (“potentials”) along the entire peripheral and central auditory pathway. This minute electrical activity is picked up by the electrodes, amplified, and averaged with a computer.

The electrical activity is displayed as a waveform with five latency-specific wave peaks. The latency of each wave peak corresponds to sites in the neural auditory pathway. In basic terms, each peak represents one anatomic structure in the auditory pathway. A tumor will slow the neural circuit and delay the waveform at the site of the lesion.

26

How do you interpret an ABR?

How do you interpret an ABR?

The mnemonic E COLI will help you to remember which structure corresponds to each waveform.

  • Wave I   Eighth nerve action potential
  • Wave II  Cochlear nucleus
  • Wave III Olivary complex (superior)
  • Wave IV Lateral lemniscus
  • Wave V  Inferior colliculus

Audiologists interpret the waveforms for proper identification and then compare them to clinical norms. Type, degree, and configuration of hearing loss can be estimated using ABR assessment. Additionally, click ABR is the gold standard for diagnosing auditory neuropathy, a less common disorder that is diagnosed by presence of a cochlear microphonic (outer hair cell function) with an absent wave I.

27

What is auditory steady state response (ASSR)?

What is auditory steady state response (ASSR)?

ASSR is an evoked potential evaluation used to estimate hearing thresholds objectively. Unlike click ABR, which assesses the mid- to high-frequency region, ASSR uses frequency-specific tonal stimulus. It assesses whether the auditory response and neurologic integrity of the auditory system are phase locked to the stimulus. Because ASSR utilizes pure-tone stimuli,the presentation intensity can be louder than traditional ABR, and is a particularly important assessment tool in differentating severe and profound hearing loss. It cannot be used to assess neurologic function.

28

What are otoacoustic emissions (OAEs)?

What are otoacoustic emissions (OAEs)?

OAEs are an objective measure that allows outer hair cell function of the cochlea to be assessed. Evoked OAEs are low-level sounds produced by the cochlea following acoustic stimulation. Transient evoked otoacoustic emissions (TEOAEs) and distortion product otoacoustic emissions (DPOAEs) are two types of OAEs used clinically. OAEs are present in patients with auditory neuropathy because OAEs are not a measure of neural function.

29

What is pseudohypacusis (also known as nonorganic hearing loss)?

What is pseudohypacusis (also known as nonorganic hearing loss)?

A number of factors may lead a person to feign a hearing loss that does not exist or exaggerate an existing hearing loss. While it is beyond the scope of this chapter to discuss some potential reasons, such as monetary gain or psychological reasons, certain outcome measures obtained from the audiogram can indicate pseudohypacusis. Based on the cross-check principle (Jerger and Hayes, 1976) all components of the audiogram should be consistent. Specifically, there should be good PTA-SRT/SAT agreement and there should be good test-retest reliability. Additionally, in a patient presenting with a unilateral hearing loss the audiologist should notice a shadow curve, meaning that once the stimulus in the poorer ear is increased to a certain loudness level (40 to 70 dB, depending on frequency and air conduction transducer) the energy would cross over to the better ear and the patient would begin to respond. However, patients who are malingering would not respond even when it becomes audible in the contralateral ear. The same is true for bone conduction, which has an interaural attenuation of 0 dB; if it is placed on the “poor” ear they will likely not respond. Another way to quantify if hearing loss truly exists when patients are feigning a unilateral loss is the Stenger test. The Stenger test can be done when there is at least a 20 dB difference between ears. It is conducted at any frequency where the difference between ears is ≥20 dB HL by presenting a tone 10 dB above the threshold in the better ear while simultaneously presenting a tone 10 dB HL below the threshold in the poorer ear. The patient should respond if the hearing loss is geniune. However, patients with nonorganic hearing loss will not respond, and this will be reported as a positive Stenger test. Additional measures discussed above (ABR and OAE) can assist in teasing out presence or absence of hearing loss.

30

When should a primary care physician be concerned about a patient’s hearing complaint?

When should a primary care physician be concerned about a patient’s hearing complaint?  Controversy

Always. All patients who suspect hearing loss or who report difficulty with speech understanding need further evaluation. Often, patients with conductive hearing problems may be successfully treated by medical or surgical means. Patients with SNHL need to be medically evaluated prior to audiologic fitting with hearing aids. Patients with a history of sudden-onset hearing loss, trauma, infection associated with the loss, or asymmetric hearing loss should be given thorough hearing tests and concurrent otolaryngologic evaluation. Symptoms of tinnitus, aural fullness, vertigo, or ear drainage also necessitate complete otolaryngologic evaluation.

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