INTRODUCTION — Hearing loss is a common problem that everyone experiences from time to time. Most commonly it occurs when flying or traveling up a mountain, and a full sensation develops in the ears, leading to the feeling of wanting to pop the ears open in order to hear better. Diminished hearing also may occur during an ear infection. These causes of hearing loss are usually short-lived. The other extreme is the permanent sensorineural hearing loss that occurs with aging, which most people experience to some degree [1].
The evaluation of hearing loss in adults will be reviewed here. The etiology and treatment of hearing loss are discussed separately. (See "Etiology of hearing loss in adults" and "Hearing amplification in adults".)
CLASSIFICATION OF HEARING LOSS — Hearing loss may be classified into three types [2]:
●Sensorineural, involving the inner ear, cochlea, or the auditory nerve.
●Conductive, involving any cause that in some way limits the amount of external sound from gaining access to the inner ear. Examples include cerumen impaction, middle ear fluid, or ossicular chain fixation (lack of movement of the small bones of the ear).
●Mixed loss, which is a combination of conductive and sensorineural hearing loss.
A number of abnormalities may lead to hearing loss of each type (table 1). It is useful to begin the evaluation by classifying the loss as sensorineural or conductive, since this helps focus the remainder of the patient assessment. Conductive hearing loss is usually related to abnormalities of the outer or middle ear; sensorineural hearing loss is related to inner ear pathology.
HISTORY — Any patient complaining of hearing loss should have a full auditory history and examination performed. Important questions in the history include:
●What was the onset and progression of the hearing loss?
●How well can the patient understand spoken words?
●Is the problem mainly with background noise (eg restaurants, parties) or is it just as bad in quiet settings?
●Is there pain or drainage out of the ear associated with the hearing loss?
●Is there a history of significant trauma, including noise and barotrauma?
●Is there a history of major infections?
●Is there a history of previous ear surgery?
●Is there associated tinnitus, vertigo, or disequilibrium?
●Is there a family history of hearing loss? There are a number of congenital and hereditary causes of hearing loss; presbycusis also can run in families.
●What medications are taken?
●Do headaches or visual disturbances occur before, during, or after episodes of hearing loss?
●What medications, including over-the-counter drugs, is the patient taking?
●History of other medical disorders such as diabetes, smoking, coronary artery disease, autoimmune diseases.
Patients with sudden hearing loss require urgent referral as treatment success is related to early initiation of treatment. (See "Sudden sensorineural hearing loss in adults: Evaluation and management".)
EXAMINATION — The examination for some patients will involve only simple tests that can be performed in a primary care office. Many patients, however, will require formal audiologic testing or other specialized tests.
Office hearing evaluation — There are a variety of methods used to test hearing in the office setting. These include a whispered voice test, tone-emitting otoscope, questionnaires, and tuning forks.
A systematic review of the whispered voice test concluded that in four studies in adults the sensitivity for hearing impairment was 90 to 100 percent and the specificity was 70 to 87 percent [3]. To perform a whispered voice test, stand at arm's length behind the patient (to prevent lip reading) and mask hearing in one ear by occluding the ear canal and rubbing the tragus with a circular motion. Whisper a short sequence of letters and numbers and ask the patient to repeat them. Test the other ear in a similar manner.
In addition to the whispered voice test, tone-emitting otoscopes and/or questionnaires are often used. In a randomized trial of screening strategies in 2305 veterans (mean age 61 years), fewer patients evaluated with a tone-emitting otoscope screened positive (19 percent versus 59 and 64 percent of patients evaluated with questionnaire and dual screening [questionnaire and otoscope], respectively) [4]. Hearing aid use one year after screening was 6 percent in the tone-emitting otoscope group compared with 4 and 7 percent in the questionnaire and dual screening groups, respectively. Screening with the tone-emitting otoscope was the most efficient screening method, as the questionnaire led to unnecessary audiology evaluations with little added benefit in terms of hearing loss detection.
Hearing status can be further assessed with tuning forks [5]. Patients who cannot hear a 256 Hz tuning fork but can hear a 512 Hz tuning fork have a hearing loss of approximately 10 to 15 dB; patients who cannot hear a 512 Hz tuning fork have an approximate loss of at least 20 to 30 dB. An ear that hears normally should have air conduction (sound waves traveling to the tympanic membrane and converted into sound in the inner ear) that is louder than bone conduction (sound transmitted via the vibration of the skull into the cochlea). The Weber and Rinne tests examine the relative adequacy of air and bone conduction of sound.
Weber and Rinne tests — The Weber and Rinne tests can help direct the remainder of the evaluation, but should not be used as screening evaluations for hearing loss [5,6].
Weber test — The Weber tuning fork test is performed by pressing the handle of the tuning fork to the bridge of the forehead, nose, or teeth and asking the patient if the sound is louder in one ear or the other. The sound is heard equally in both ears in patients with normal hearing or symmetric hearing loss.
Rinne test — The Rinne test allows comparison of sound when the tuning fork is placed on the mastoid bone behind the ear (bone conduction), versus when the tuning fork is held near the ear (air conduction) [7,8]. An abnormal result occurs when sound is at least equally loud or louder when the fork is placed on bone as compared with when it is held next to the ear (bone>air conduction). The Rinne test is considered normal when the vibrating fork placed near the ear is louder than when placed on the mastoid bone (air>bone conduction).
One method for performing the Rinne test is to press the handle of the tuning fork to the mastoid bone and ask the patient to tell the examiner when the sound is no longer audible. At that point, the vibrating end of the tuning fork is placed near the external auditory canal (EAC). If the patient can again hear the tuning fork, the Rinne test is normal.
Interpretation — The Weber and Rinne tests can then be used to help distinguish conductive from sensorineural hearing loss (table 2 and figure 1):
●In patients complaining of a unilateral decrease in hearing, the Weber test suggests sensorineural hearing loss if the sound lateralizes (is louder on) to the "good" side; conductive hearing loss is suspected if the sound lateralizes to the "bad" side.
●An abnormal Rinne test, with bone>air conduction, is consistent with conductive loss, particularly if the Weber test also lateralizes to that side.
●When the Weber test lateralizes to an ear in which the Rinne is normal, the Rinne test in the opposite ear should be performed. A normal Rinne test in the contralateral ear suggests sensorineural hearing loss in this contralateral ear (ie, the Weber lateralized to the normal ear). An audiogram is indicated in this situation.
The Weber test may be unreliable in some settings. In one study of 250 patients with sudden sensorineural hearing loss (SSNHL) confirmed by audiometry, the Weber test correctly identified sensorineural hearing loss in the affected ear in 78 percent; the Weber test did not lateralize in 21 percent (heard midline or not heard at all), and incorrectly lateralized in just 1 percent [9]. These results suggest that in the setting of sudden hearing loss, further evaluation for SSNHL is required when the Weber test does not lateralize. (See "Sudden sensorineural hearing loss in adults: Evaluation and management".)
Conductive hearing loss on one side is indicative of external or middle ear disease (table 1). (See "Etiology of hearing loss in adults", section on 'Outer ear causes' and "Etiology of hearing loss in adults", section on 'Middle ear causes'.)
Gradual sensorineural hearing loss on one side suggests an inner ear disorder such as Meniere disease or a vestibular schwannoma (acoustic neuroma). If confirmed by audiometry, the patient with progressive asymmetric sensorineural hearing loss that is not clearly attributed to Meniere disease should have an MRI or CT scan of the posterior fossa and internal auditory canal. (See "Meniere disease: Evaluation, diagnosis, and management" and "Vestibular schwannoma (acoustic neuroma)".)
Examination of the ear — Patients with conductive hearing loss should have an examination of the auricle and EAC performed to look for blockage of the EAC. The tympanic membrane (TM) should be viewed to ensure that there is no middle ear abnormality such as fluid or TM perforations.
Pneumoscopy — Pneumoscopy is also performed to evaluate mobility of the TM. Positive pressure that forces air into the EAC thereby pushing down the TM, is done first. The pressure is then released, with the subsequent negative pressure pulling the TM outwards.
●A nonmobile TM may occur because of fluid in the middle ear cavity, a mass in the middle ear cavity, or a stiff or sclerotic TM.
●A hypermobile TM may indicate ossicular chain disruption.
●The TM may only move with negative pressure; this can be caused by retraction of the TM or middle ear with a blocked eustachian tube, resulting in negative middle ear pressure.
Formal audiologic assessment — Patients without an obvious etiology for hearing loss (such as external otitis or cerumen impaction) should undergo formal audiologic testing [10]. Formal audiologic assessment is performed by an audiologist in a soundproof environment. This evaluation provides very accurate and detailed information regarding a patient's hearing ability. The formal audiogram, with tympanogram and site of lesion testing, provides definitive information. Every audiologic workup should consist of a number of audiometric studies [11].
Pure tone, air, and bone conduction testing — Pure tone testing is commonly known as the audiogram. The patient is in a soundproof booth, and the audiologist assesses the sensitivity or ability to hear pure tone stimuli at the frequencies of 250, 500, 1000, 2000, 4000, and 8000 hz. The threshold for each stimulus is determined by finding the dB level at which the patient can detect the tone 50 percent of the time [12].
Hearing is tested with both air and bone conduction. Air conduction tests the ability to hear with ear phones via the normal mechanism of hearing: sound through the EAC, TM, and the middle ear system. Bone conduction is tested with a bone oscillator. The oscillator is placed on either mastoid and held in place, stimulating noise going into the skull and bypassing the middle ears by setting the fluid and cochlea in motion directly with bone vibration.
Measuring and comparing both air and bone conduction may be helpful in determining the etiology of the hearing loss. Any difference between air and bone conduction thresholds is known as an air/bone gap; a gap is consistent with conductive hearing loss (figure 2). In addition, the specific pattern of bone conduction may provide further information about the etiology of the hearing loss. As an example, in otosclerosis, a notch may be observed at approximately 2000 Hz (“Carhart’s notch”), which represents a partial closure of the air-bone gap at this frequency [13].
Speech audiometry — Speech audiometry typically consists of two parts: the speech reception threshold (SRT) and the word discrimination score.
●The SRT is the softest level at which a patient can correctly repeat 50 percent of presented spondee words. Spondee words are two-syllable words where each syllable is stressed, such as airplane, armchair, or pancake. SRT is recorded in decibels and serves as a cross-check for the pure tone air conduction thresholds. The SRT is typically equal to the pure tone air conduction average, ± 6 dB [14]. The pure tone average is the average decibel score at 500, 1000, and 2000 hz.
●The word discrimination score is the percentage of phonetically balanced words that a patient can correctly repeat at a given sensation level. Typically, testing is performed at 40 dB above the patient's SRT. This discrimination score serves two purposes: it can establish the prognosis for the use of a hearing aid, and it helps determine the site of the lesion. A poor discrimination score usually indicates significant neural degeneration; these individuals may not be good candidates for hearing aids, since the aid will amplify sound but may not allow the patient to understand what is being said.
Impedance audiometry — Impedance audiometry is performed in two parts: tympanometry and stapedial reflex testing [15,16].
●Tympanometry – Tympanometry is the “hard-copy” version of pneumoscopy. It is an objective measure of the changes in the acoustic impedance of the middle ear system in response to changes in air pressure. As the pressure increases during pneumoscopy, the eardrum is pushed medially; as negative pressure is placed, the eardrum protrudes laterally. The point of maximum compliance of the middle ear is identified; this indicates the current status of the air pressure in the middle ear.
Five types of tympanograms can be seen (figure 3):
•Type A – Normal middle ear pressure
•Type B – Little or no mobility, suggestive of fluid behind the TM
•Type C – Negative pressure in the middle ear suggestive of a retracted TM
•Type AS – A very stiff middle ear system that may be due to myringosclerosis or otosclerosis
•Type AD – A highly compliant TM usually seen in ossicular chain discontinuity
●Stapedial reflex testing – Stapedial reflex testing may also be performed [17]. Further discussion of this test is beyond the scope of this review.
Other audiologic tests — Auditory brainstem response (ABR) testing is commonly done in infants to assess hearing but can also be done to assess hearing in adults who either cannot cooperate with a traditional hearing test, may have a functional component, or exhibit a unilateral sensorineural hearing loss and when further evaluation in lieu of an MRI is needed to assess for central pathology [18-20].
Other tests — Various metabolic abnormalities have been known to either cause or be associated with sensorineural hearing loss. Thus, an evaluation of an unexplained sensorineural hearing loss should involve a complete laboratory evaluation to include the following:
●Measurement of blood sugar; small vessel disease as a result of diabetic vasculopathy can cause cochlear ischemia.
●Complete blood count with differential; anemia or a white blood cell dyscrasia may lead to sensorineural hearing loss by an unknown mechanism that may involve decreased oxygenation, microblockage of vessels, or infection.
●Thyroid stimulating hormone to rule out hyper or hypothyroidism.
●Serologic test for syphilis.
●Serologic tests for Sjogren's syndrome (ANA, RF, anti-Ro and anti-La) in patients who have dry eyes or dry mouth. (See "Neurologic manifestations of Sjögren's syndrome", section on 'Multiple cranial neuropathies'.)
●Patients with unexplained conductive hearing loss should have a CT scan of the temporal bone.
●Patients with unilateral, fluctuating, or unexplained asymmetric sensorineural hearing loss should have an MRI with gadolinium.
●Patients with loss other than presbycusis (hearing loss of aging) should be evaluated by an ENT.
●Patients whose hearing loss is not improved by traditional hearing aids should be considered for evaluation by a center that performs various types of implants for hearing (eg, cochlear implants, Baha implants, or middle ear implants of various types).
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Hearing loss and hearing disorders in adults".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topics (see "Patient education: Age-related hearing loss (presbycusis) (The Basics)" and "Patient education: Ear wax impaction (The Basics)")
SUMMARY AND RECOMMENDATIONS
●Initial office evaluation of patients with hearing loss – Patients with hearing loss may have conductive, sensorineural, or mixed hearing loss. Patients with hearing loss should undergo a directed history and examination (table 1). The evaluation should include:
•A comprehensive clinical history (see 'History' above)
•An office test of hearing (see 'Office hearing evaluation' above)
•Weber and Rinne tests to distinguish conductive from sensorineural hearing loss (figure 1 and table 2) (see 'Weber and Rinne tests' above)
●Physical examination in conductive hearing loss – Patients with conductive hearing loss (table 1) should undergo physical examination of the auricle and external auditory canal (EAC) looking for evidence of blockage to explain the hearing loss. (See 'Examination of the ear' above.)
●Formal audiology testing if the cause is uncertain – Patients without an obvious etiology for hearing loss (such as external otitis or cerumen impaction) should undergo formal audiologic testing. (See 'Formal audiologic assessment' above.)
●Additional testing may be warranted in some patients. (See 'Other tests' above.)
•Patients with an unexplained sensorineural hearing loss should have the following laboratory tests: blood sugar, complete blood count with differential, thyroid-stimulating hormone, and serologic test for syphilis.
•Patients with progressive asymmetric sensorineural hearing loss should have an MRI with contrast, and those with unexplained conductive hearing loss a CT scan of the posterior fossa and internal auditory canal to exclude disorders such as vestibular schwannoma (acoustic neuroma).
•Patients with hearing loss where the etiology is unclear generally require referral to an otolaryngologist or ENT clinician; patients with sudden sensorineural hearing loss require urgent referral as treatment success is related to early initiation of treatment.
