Conductive vs sensorineural hearing loss tuning fork

Weber Test

The examiner places the base of a vibrating tuning fork on the midline vertex of the patient’s head. The patient should hear the sound equally well in both ears (Fig. 2.65). If the patient hears better in one ear (i.e., the sound is lateralized), the patient is asked to identify which ear hears the sound better. To test the reliability of the patient’s response,the examiner repeats the procedure while occluding one ear with a finger and asks the patient which ear hears the sound better. It should be heard better in the occluded ear.189,190

10.6.1.2 Weber Test

The Weber test is a test for lateralization. Tap the tuning fork strongly on your palm and then press the butt of the instrument on the top of the patient’s head in the midline and ask the patient where they hear the sound. Normally, the sound is heard in the center of the head or equally in both ears. If there is a conductive hearing loss present, the vibration will be louder on the side with the conductive hearing loss. If the patient does not hear the vibration at all, attempt again, but press the butt harder on the patient’s head.

The Weber test

SeeVideo 11.5

In the Weber test, BC is compared in both ears, and the examiner determines whether monaural impairment is neural or conductive in origin. Stand in front of the patient and place a vibrating 512-Hz tuning fork firmly against the center of the patient's forehead. Ask the patient to indicate whether he or she hears or feels the sound in the right ear, in the left ear, or in the middle of the forehead. Hearing the sound, or feeling the vibration, in the middle is the normal response. If the sound is not heard in the middle, the sound is said to belateralized, and thus a hearing loss is present. Sound is lateralized to theaffected side in conductive deafness. Try it on yourself. Occlude your right ear and place a vibrating tuning fork in the center of your forehead. Where do you hear it? On theright. You have created a conductive hearing loss on the right by blocking the right canal; the sound is lateralized to the right side. The Weber test is illustrated inFig. 11.13.

The explanation for the Weber test effect is based on the masking effect of background noise. In normal conditions, there is considerable background noise, which reaches the tympanic membrane by AC. This tends to mask the sound of the tuning fork heard by BC. In an ear with a conductive hearing loss, the AC is decreased, and the masking effect is therefore diminished. Thus, the affected ear hears and feels the vibrating tuning fork better than does the normal ear.

In patients with unilateral sensorineural deafness, the sound is not heard on the affected side but is heard by, or localized to, theunaffected ear.

To test the reliability of the patient's responses, it is occasionally useful to strike the tuning fork against the palm of the hand and hold it briefly to silence it. The Rinne and Weber tests are then carried out as indicated, using the silent tuning fork. This serves as a good control.

In summary, consider the following two examples:

Example 1

Rinne:Right ear: AC > BC (Rinne positive—normal);left ear: AC > BC (Rinne positive—normal)

Weber: Lateralization to the left ear

Diagnosis: Right sensorineural deafness

Example 2

Rinne:Right ear: AC > BC (Rinne positive—normal);left ear: BC > AC (Rinne negative—abnormal)

Weber: Lateralization to the left ear

Diagnosis: Left conductive deafness

AC, Air conduction;BC, bone conduction;CD, conductive deafness;SCL, combined loss (sensorineural and conductive);SN, sensorineural deafness.

Weber Test

The Weber test is a test for lateralization. Tap the tuning fork strongly on your palm and then press the butt of the instrument on the top of the patient’s head in the midline and ask the patient where they hear the sound. Normally, the sound is heard in the center of the head or equally in both ears. If there is a conductive hearing loss present, the vibration will be louder on the side with the conductive hearing loss. If the patient doesn’t hear the vibration at all, attempt again, but press the butt harder on the patient’s head.

Approach to Treatment (Table E1)

•

The first step in evaluating hearing complaints is to ascertain the location and extent of the hearing loss.

The history must include details about the timing of hearing loss, laterality, previous episodes, associated symptoms (tinnitus, vertigo, or pain), preceding events (diving, plane rides, trauma), potential placement of a foreign body, environmental noise exposure, and potential ototoxic drugs.

Tuning fork tests provide the best clues to distinguish between conductive and sensorineural hearing loss.

TheWeber test compares the two ears with each other (Fig. E2). A vibrating fork is placed midline on the top of the head. The patient is asked which ear hears the vibrations better. If the fork is heard louder in one ear, either that ear has a conductive deficit or the other ear has a neural deficit (Table E2).

TheRinne test evaluates each ear independently (Fig. E2). Normally, air conduction is more sensitive than bone conduction, and one should be able to hear a vibrating fork longer through the air than through bone. The handle of a vibrating fork is placed on the mastoid process of the side being evaluated. The vibrating end is then held near the ear canal. Normally functioning ears hear the air conduction louder and longer than the bone conduction. Perception of sound better through bone conduction indicates a conductive deficit. Lack of hearing either bone or air conduction points to sensorineural hearing loss (Table E2).

TABLE E1. Lesions That Cause Hearing Loss

ASA, Acetylsalicylic acid;BP, blood pressure;CNS, central nervous system;CSF, cerebrospinal fluid;CVA, cerebrovascular accident;ENT, ear, nose, and throat;SNHL, sensorineural hearing loss;TM, tympanic membrane;URI, upper respiratory infection.

From Adams JG:Emergency medicine: clinical essentials, ed 2, Philadelphia, 2013, Elsevier.

TABLE E2. Interpretation of the Weber and Rinne Tests

AC, Air conduction;BC, bone conduction;S/N, sensorineural.

From Adams JG:Emergency medicine: clinical essentials, ed 2, Philadelphia, 2013, Elsevier.

Weber

The Weber test is used in conjunction with the Rinne test and is most useful in patients with unilateral hearing loss. The aim is to identify the better-hearing cochlea. The 512-Hz tuning fork is struck and placed in the midline on either the forehead or the vertex. The patient is asked if the sound is heard louder in one ear or equally in both ears. In a normally hearing patient, the tone is heard centrally. Otherwise, the sound is heard on the side of the better cochlea unless there is a conductive hearing loss, in which case the tone may be heard in the poorer-hearing ear.

4 Weber Test

In the Weber test the clinician strikes the fork, places it in the middle of the patient’s vertex, forehead, or bridge of nose, and asks “Where do you hear the sound?” (Fig. 24.2). In patients with unilateral hearing loss the sound is preferentially heard in the good ear if the loss is neurosensory and in the bad ear if the loss is conductive.8,14 Weber himself recommended placing the vibrating fork on the incisors15 and subsequent studies do show this is the most sensitive technique,16 although concerns of transmitting infectious diseases now prohibit this method.

According to traditional teachings, persons with normal hearing perceive the sound in the midline or inside their head, but studies show that up to 40% of normal-hearing persons also lateralize the Weber test.11 Therefore the Weber test should be interpreted only in patients with hearing loss.

NEURO-OTOLOGICAL TESTS

Vestibulocochlear Nerve

The vestibulocochlear nerve mediates hearing and balance. Hearing can be assessed with a 512-Hz tuning fork. The Rinne and Weber tests are commonly used to assess for sensorineural and conductive deafness.

In the Weber test, the base of a gently vibrating tuning fork is placed on the midforehead or the vertex. The patient is asked which ear hears the sound better. Normally, the sound is heard equally in both ears. With unilateral sensorineural hearing loss, sound is heard better in the unaffected ear. With unilateral conductive hearing loss, sound is heard better in the affected ear.

The Rinne test is conducted by placing the base of a gently vibrating tuning fork on the mastoid bone behind the ear. When the patient can no longer hear the sound, the fork is quickly moved next to the patient’s ear. In patients with sensorineural deafness and normal hearing, air conduction is better than bone conduction. With conductive deafness, bone conduction is better than air conduction.

Nystagmus noted on eye movement testing may be a sign of vestibular dysfunction. In patients with complaints of episodic vertigo, the Dix-Hallpike maneuver is useful for making the diagnosis of benign paroxysmal positional vertigo.

Cranial nerve VIII, hearing

In the neurological evaluation for dementia, any functional change in an individual with DS needs to have an assessment of hearing. The Rinne and Weber tests are often too complex for an individual with DS and yield inconsistent results. We have found that an office substitute comprises whispering a word in each ear and asking the participant to repeat it. This is admittedly not very precise but gives an idea as to whether a serious hearing loss may be present. An inspection of the ear canal may reveal blockage by cerumen and/or a structural problem with the tympanic membrane. The examiner should have a low threshold for referring the individual with DS for a formal audiological assessment as indicated. The prevalence of hearing loss in adults with DS is striking with increases from 43% in the 20–29 year old age group to over 90% at ages 50–59 years [134, 135]. The audiometric profiles in aging adults with DS are similar to that seen in presbycusis within the general population. Adding to the problems of sensorineural hearing loss in DS are dysplastic ear canals stemming from structural abnormalities in middle ear, Eustachian tubes, and midface configurations in DS [136]. In the general population, hearing loss accounts for at least 9% of cases of dementia [137] and audiological treatment has been associated with cognitive improvements [138].