The Weber Test - Indications, Contraindications

The Weber test is a useful, quick, and simple screening test for the evaluation of hearing loss. The test can detect unilateral conductive and sensorineural hearing loss. The outer and middle ear mediate conductive hearing. The inner ear mediates sensorineural hearing. The Weber test is often combined with the Rinne test to detect the location and nature of hearing loss.

Anatomy and Physiology

To understand the Weber test, one has to understand the basic anatomy of hearing.

The ear anatomically consists of the sound-conducting system (outer and middle ear) and sound-transducing system (the cochlea).

The outer ear: Pinna and external ear canal
The middle ear: Tympanic membrane, ossicular chain (malleus, incus, stapes) and middle ear space
The inner ear: Cochlea (organ of hearing), vestibular labyrinth (organ of balance)

The purpose of the outer ear is to direct sounds onto the tympanic membrane. The sound vibrations are then transmitted through the middle ear via the ossicular chain before it reaches the cochlea. The cochlea plays an important role in transducing these vibrations into nerve impulses via the auditory nerve (vestibulocochlear nerve) which is then delivered along the central pathways to the auditory cortex where it is processed and perceived as sound. This pathway is termed air conduction. However, sound can also be transmitted via bone conduction where vibrations are transmitted via the skull and delivered directly to the cochlea which is buried within the temporal bone.

Hearing loss may occur due to interruption at any point along these pathways.

The Weber test, along with its paired Rinne test, is commonly used to distinguish the site and likely cause of hearing loss. Conductive hearing loss is due to problems with the sound-conducting system, while sensorineural hearing loss is due to problems with the sound-transducing system, the auditory nerve or its central pathways. Occasionally, one can get a mixed hearing loss, which is a combination of the 2 hearing loss.

Indications

In normal hearing, an individual will hear equally on both sides of the ear. The Weber test is a test of lateralization and is of most value useful in those with an asymmetrical hearing loss.

Weber Test Principles

The inner ear is more sensitive to sound via air conduction than bone conduction (in other words, air conduction is better than bone conduction).

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In the presence of a purely unilateral conductive hearing loss, there is a relative improvement in the ability to hear a bone-conducted sound. This can be explained by the following:

Masking effect – The sound heard via the affected ear has less environmental noise reaching the cochlea via air conduction (for example, the environmental noise is masked) as compared to the unaffected ear which receives sounds from both bone conduction and air conduction. Therefore, the affected ear is more sensitive to bone-conducted sound.
Occlusion effect – Most of the sound transmitted via bone conduction travels through to the cochlea. However, some of the low-frequency sounds dissipate out of the canal. A conductive hearing loss (in other words, when an occlusion is present) will, therefore, prevent external dissipation of these frequencies and lead to increased cochlear stimulation and increased loudness in the affected ear.

In the presence of sensorineural hearing loss, the sound will be perceived louder in the unaffected ear which has the better cochlear.

Equipment

An ideal tuning fork of choice for the Weber test would be one that has a long period of tone decay, in other words, the tone maintains/lasts long after the tuning fork has been struck, and cannot be detected by sense of bone vibration, therefore preventing misinterpretation of the vibration as sound.

512-Hz Tuning Fork – In clinical practice, the 512-Hz tuning fork has traditionally been preferred. At this frequency, it provides the best balance of time of tone decay and tactile vibration. Lower-frequency tuning forks like the 256-Hz tuning fork provide greater tactile vibration. In other words, they are better felt than heard. Higher-frequency tuning forks, for example, the 1024-Hz tuning fork, have a shorter tone decay time.
256-Hz Tuning Fork: An Alternative – The 256-Hz tuning fork, along with 128-Hz tuning fork, is commonly used as part of neurological examination due to their greater tactile vibration characteristic. However, evidence suggests that the 256-Hz provides better reliability when compared to the 512-Hz. [rx],[rx]

Preparation

Ideally, the test should be carried out in a quiet room
Verbal consent should be gained prior to performing the test
Clear instructions should be given to the patient to avoid misinterpretation of the test

Technique

Tuning Fork

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The audiometric tuning fork generally consists of the tines (the U-shaped prongs), the stem, and the footplate.

Striking the Tuning Fork

Hold the tuning fork by the stem between the thumb and first finger.
Strike the tines one-third of the way from the free end of the prong onto a firm but the elastic object (e.g., the clinician’s knee or elbow). This will produce a relatively pure tone.
Avoid striking the tines onto a hard surface as this may damage the tuning fork and produce multiple overtones.

Performing Weber Test [rx]

Place the vibrating tuning fork on the vertex (other common sites used are the midline of the forehead, bridge of the nose, and chin), equidistant from both ears. These vibrations will be conducted through the skull and reach the cochlea.
Ask the patient whether it is heard loudest in either one side or the midline (e.g., “Is the sound louder in your right ear, left ear, or the middle?”)

Interpretation

Normal Hearing

Weber test does not demonstrate lateralization: In a normal subject, the sound should be heard in the middle and equally on both sides.
Rinne test: Normal/positive in both ears (AC greater than BC)

Unilateral Sensorineural Hearing Loss

Weber test lateralizes to the unaffected ear, in other words, it is heard louder in the better ear.
Rinne test: Normal/positive on the affected ear (AC greater than BC); normal/positive on the unaffected ear (AC greater than BC)

Note: an abnormal/negative response on the affected ear (BC greater than AC) can also occur in a severe sensorineural hearing loss, also called a dead ear. This is termed a “false negative.” Rinne “true negative” only occurs if there is a conductive hearing loss element. However, when testing a dead ear, the bone conduction is perceived to be heard louder than air conduction due to cross-over of bone conduction detected by the opposite normal-functioning cochlear, resulting in a Rinne false negative.

Unilateral Conductive Hearing Loss

Weber test lateralizes to the affected ear, in other words, it is heard louder in the poorer ear.
Rinne test: Abnormal/negative on the affected ear (BC greater than AC); normal/positive on the unaffected ear (AC greater than BC)

Symmetrical Conductive Hearing Loss

Weber test does not demonstrate lateralization
Rinne test: Abnormal/negative on the affected ear (BC greater than AC)

Complications

The Rinne test is the complement for the Weber test. They are screening tests and do not replace formal audiometry. It is important to note that further examinations and investigations such as otoscopy, audiometry, tympanometry, and imaging may be required to correctly diagnose the cause of the hearing loss and allow appropriate management.

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Clinical Significance

Clinical Use

In the primary care setting, it is useful to use the Weber test along with Rinne test to help the clinician differentiate between conductive hearing loss with a sensorineural hearing loss. This will guide the clinician to the need for further examination, investigation, and management.
In the post-operative setting, the test is commonly used as a quick bedside test for examining a complication of a dead ear (complete sensorineural hearing loss).
The Weber and Rinne tuning fork tests can be used to confirm audiometric findings, particularly when the audiogram is not consistent with clinical findings
In the assessment of a patient with bilateral conductive hearing loss, the Weber test is a quick and useful test for the otorhinolaryngology (ENT) surgeon to help determine which side of the ear to operate on first. Usually, the ear with the more significant conductive hearing loss is preferred.[rx][rx][rx]

Possible Causes (Non-Exhaustive) of Hearing Loss

Conductive Hearing Loss

Outer Ear Causes

Impacted wax
Infection affecting the outer ear (otitis externa)
A foreign body within the external ear canal
Squamous cell carcinoma
Congenital microtia

Middle Ear Causes

Tympanic membrane trauma
Infection affecting the middle ear (acute otitis media)
Glue ear (otitis media with effusion)
Otosclerosis
Cholesteatoma
Congenital malformation
Temporal bone trauma

Sensorineural Hearing Loss

Inner Ear Causes

Hereditary hearing loss
Presbycusis
Labyrinthitis
Meniere disease
Viral cochleitis
Vascular insult
Autoimmune conditions
Noise exposure
Vestibular schwannoma
Ototoxic drugs
Trauma

References