When performing the Weber test on a patient with a conductive hearing loss in the left ear the patient would hear the tone best in which ear?

Classically the Weber test can be useful in detecting a unilateral sensorineural hearing loss or a unilateral conductive hearing loss. In patients with a unilateral sensorineural hearing loss, a positive Weber result is obtained in the contralateral normal ear, with sounds being heard louder on this side. When a unilateral conductive hearing loss is present a positive test result is obtained in the affected ear, where sounds are perceived louder despite the hearing deficit. However, as Dr. Weatherall points out, the intensity of sounds reaching the cochlea transmitted via the bony skull should be equal in both ears when inner ear function is normal. In addition the normal ear should be receiving additional sound energy via the air conduction route. So how can one explain a positive Weber test in patients with a unilateral conductive

loss?

There are four explanations for the Weber phenomenon. The first suggests it is due to a masking effect. That is, sound heard in the blocked ear seems louder than in the normal ear as there is less background noise reaching the cochlea via air conduction. Thus sound heard in a background of silence seems louder than the same sound obscured by excessive ambient noise. The second more physiological explanation is based on the fact that there are more efferent fibres than afferent fibres in the cochlear nerve. Air conduction of sound into the blocked ear is reduced, resulting in a discrepancy between the sound energy reaching the two cochleas. This inequality is detected in the brainstem nuclei, and a compensatory mechanism is activated which increases the innate gain of the cochlea on the side receiving less stimulation. Any sound energy reaching the cochlea directly via skull vibration is consequently amplified. Thirdly, it is now known that when sound enters the ear most is transmitted via the cochlea along the central pathways to the auditory cortex, but outer hair cell vibrations cause a significant amount of "reflected" sound, the so-called "cochlear echo" described by Kemp in 19782. This transient evoked otoacoustic emission can be recorded in the ear canal using a microphone, and would normally dissipate outwards into the air. A conductive hearing loss due, for example, to fixation of the ossicular chain or occlusion of the external meatus will prevent this external dissipation of sound energy, resulting in increased cochlea stimulation and apparent increased loudness. Lastly, the skull acts as a resonating chamber. Any change in the properties of this chamber, such as occlusion of the external canal with wax, will change the resonance of

sound within the medial part of the canal.

Although these explanations give some credence to the Weber phenomenon, clinical trials have demonstrated that the test is highly unreliable. Bilateral hearing impairment understandably causes major difficulties in interpretation. However, even in patients with a documented unilateral hearing impairment 30 per cent will refer the Weber to the midline. Moreover, of 70 per cent of patients with a positive Weber about 25 per cent have been shown to lateralise the test result to the incorrect ear 3,4. Furthermore, patients with cochlear hearing losses display the phenomenon of recruitment, in which sounds are perceived as abnormally louder in the affected ear due to a defect of the inner ear dampening mechanisms. Providing the level of sensory hearing impairment is only modest, a positive Weber result may in fact be obtained with an

early sensorineural hearing loss as well.

In reality, the Weber test is mainly used in our department as a crude method of excluding a post-operative dead ear on the morning ward round, and of course for testing the ingenuity of the Senior House Officer in finding a tuning fork on the surgical ward. Patients presenting to the Out-Patient department undergo a pure tone audiogram for more accurate

assessment of their hearing loss.

Kay Seymour
Senior SHO

Natalie Brookes
Specialist Registrar,

Simon Lloyd
Specialist Registrar,

Hesham Saleh
Consultant.

Department of Otolaryngology/Head & Neck Surgery, Charing Cross Hospital, Fulham Palace Road,

London SW6 8RF.

Contact e-mail address:

No competing interests.

References

1. Weatherall MW. The mysterious Weber's test. BMJ 2002;325:26.

2. Kemp DT. Stimulated acoustic emissions from within the human auditory
system. J Acoust Soc Amer 1978;64:1386-91.

3. Stankiewicz JA, Mowry HJ. Clinical accuracy of tuning fork tests.
Laryngoscope 1979;89(12):1956-63.

4. Browning GG. Clinical Otology and Audiology (2nd Ed). 1998 Butterworth
Heinmann: 12-13.

Competing interests: No competing interests

Dept of Otolaryngology, Charing Cross Hospital

How to do Rinne and Weber tuning fork tests for doctors, medical student finals, OSCEs and MRCP PACES

Background to the tuning fork tests

• The tuning fork tests provide a reliable clinical method for assessing hearing loss
• They are most useful in patients with unilateral hearing loss which is purely conductive or purely sensorineural
  • Patients with bilateral loss or mixed losses are better assessed with formal pure tone audiometry
• These tests should be carried out with a full examination of the cranial nerves or the ear
• The Rinne and Weber tests help distinguish between a conductive hearing loss (CHL) and sensorineural Hearing Loss (SHL)
  • Other tuning fork tests include the Schwabach and Bing tests, though these are not used in routine practice

Video on Rinne and Weber tests by Oxford Medical Education

Introduction (WIIPPPE)

• Wash your hands
• Introduce yourself (name and position)
• Identity of patient (confirm name and date of birth)
• Permission (consent and explain examination: “I’m going to examine your hearing using this tuning fork now, is that OK?”)
• Pain (especially over the mastoid)
• Position (sitting comfortably)
• Exposure

Equipment

• A 512 Hz tuning fork
• Note you should ideally be in a completely silent room for Rinne and Weber tests

How to do Weber’s Test

• To perform Weber’s test strike the fork against your knee or elbow, then place the base of the fork in the midline, high on the patient’s forehead
  • It is important to steady the patient’s head with your other hand so that reasonably firm pressure can be applied
• Then ask the patient: “Do you hear the sound louder in one ear than the other?”
  • If so, in which ear is it louder?
  • If the patient is unclear, you may ask if they hear it “everywhere.” Be careful not to ask the question in a leading manner

Interpretation of Weber’s test

• Weber’s test will ‘lateralise’, i.e. move to one side, with a relatively small amount of hearing loss (5dB)
• If a patient has a unilateral conductive hearing loss, the tuning fork sound will be heard louder in the deaf ear
• If a patient has a unilateral sensorineural hearing loss, the tuning fork sound will be heard louder in the normal ear
• In bilateral and symmetrical hearing loss of either type Weber’s test will be normal
• The various outcomes of Rinne and Weber tests are shown below

Interpretation of Rinne’s and Weber’s tests

How to do Rinne’s Test

• This test aims compare air conduction with bone conduction
  • Rinne’s test has a high sensitivity (0.84) though this varies with the skill of the examiner
  • Rinne’s test can only detect a conductive hearing loss of at least 30dB
• Explain the test first:
  • “I’m going to put this vibrating tuning fork in two positions, one touching the bone near you ear, one a short distance from the ear. I want you to tell me which position you hear the tuning fork loudest in”
• Begin by striking the tuning fork against your knee or elbow
• Hold the tuning fork in one hand and place the base against the patient’s mastoid process (see video)
  • Allow it to stay there for 2-3 seconds to allow them to appreciate the intensity of the sound
• Then promptly lift the fork off the mastoid process and place the vibrating tips about 1cm from their external auditory meatus
  • Leave it there again for a few seconds before taking the tuning fork away from their ear
• Ask the patient in which of the positions they were able to hear the note the loudest in

What is a positive and negative Rinne’s Test?

• A patient who hears the tuning fork loudest when held 1cm from the external auditory meatus has a positive Rinne’s test
• A patient who hears the fork loudest when it is held against the mastoid process has a negative Rinne’s test

Interpretations of Rinne’s Test

• In a normal ear sound is conducted to the cochlear most efficiently via air conduction. Sound can also be transmitted to the cochlea, less efficiently, via bone
• So…
  • 1) If a patient can hear best when the tuning fork is in the air (positive Rinne’s) then air conduction is better than bone conduction so there is no significant conductive hearing loss
    • Therefore in sensorineural hearing loss on the right, for example, Rinne’s test should be positive on the right
  • 2) If the patient can hear best when  the tuning fork is on the mastoid (negative Rinne’s) bone conduction is better than than air conduction, demonstrating a conductive hearing loss

False negative Rinne’s Test

• The difficulty in interpreting Rinne’s test is in total unilateral sensorineural hearing loss (i.e. a ‘dead’ ear)
• For example, imagine the right ear is ‘dead’. On testing bone conduction on the right the sound travels to the good left (i.e. untested) ear and sounds louder than when the fork is held next to the external auditory meatus on the side being tested
• The patient reports that bone conduction is better than air conduction giving a false negative Rinne’s test

Complete the examination

• Thank the patient, make sure they’re comfortable and ask if they need any help in getting dressed
• Wash your hands
• In an exam, then turn to examiner with your hands behind back holding your stethoscope, before saying: “To complete my examination, I would like to…”
  • Take a full history
  • Perform formal pure tone audiometry if there is any concern about hearing loss
  • Do a cranial nerve examination if any concern of damage to other cranial nerves

Click here for qustions about the auditory nerve (8th nerve)

Perfect revision for medical student finals, OSCES and PACES