Timothy C. Hain, MD.
Last update: 6/2002
Hearing loss is very common, especially in the older population. This page provides a general overview for the diagnosis and evaluation of hearing loss.
The outer ear consists of the auricle, the external auditory canal, and the lateral surface of the tympanic membrane (TM). The middle ear includes the medial surface of the eardrum, the ossicular chain, the eustachian tube, and the tympanic segment of the facial nerve. The inner ear includes the auditory-vestibular nerve, the cochlea and the vestibular system (semicircular canals). The auditory nerve, also called the cochlear nerve, transmits sound to the brain.
There are three "pure" types of hearing loss encountered commonly in clinical practice: sensorineural, conductive, and central. A fourth type, denoted "mixed", is simply a combination of sensorineural and conductive.
Disorders of the middle ear are generally responsible for conductive losses. Disorders of the cochlea or cochlear nerve for sensorineural hearing loss, and disorders of the brainstem or brain account for central hearing loss.
Sensorineural hearing loss is the most common type of hearing loss, occurring in 23% of population older than 65 years of age. The term "sensorineural" is used to indicate that there is either a cochlear or an eighth nerve lesion. The diagnosis of a sensorineural pattern hearing loss is made through audiometry, which shows a significant hearing loss without the "air-bone gap" that is characteristic of conductive hearing disturbances. Common causes include old age, where the hearing pattern is often called presbyacusis (see following section), Menieres disease, ototoxic medications (such as high-dose aspirin or certain strong diuretics), immune disorders, and noise exposure (see following section). Trauma (inner ear concussion) can cause both temporary and permanent hearing loss.
Infections such as meningitis are a common cause of hearing loss in children where it occurs in approximately 20% of those with streptococcus pneumoniae meningitis (Dichgans et al, 1999). Postmeningitic hearing loss can be due to lesions of the cochlea, brainstem and higher auditory pathways, but usually is related to suppurative labyrinthitis (cochlear).
There are many causes of sensorineural hearing loss that are extremely rare. Tumors in general are a very rare cause of sensorineural hearing loss. Examples are acoustic neuroma and glomus tumor. Hyperviscosity syndromes such as Von Waldenstroms macroglobulinemia are another rare cause. Superficial siderosis, due to CNS bleeding, can cause a slowly progressive sensorineural hearing loss as well as cerebellar or vestibular disturbances. Kawasacki's disease is a rare cause of hearing loss in children.
Noise is a common cause of hearing loss in the US. Twenty-five percent of the US work force is regularly exposed to potentially damaging noise (Suter and von Gierke, 1987). Because of occupational risk of noise induced hearing loss, there are government standards regulating allowable noise exposure. People working before the mid 1960's may have been exposed to higher levels of noise where there were no laws in the USA mandating use of devices to protect hearing. An example of a noise induced hearing loss is shown below. There is a clear "notch" at 3000 hz, with better hearing at both lower and higher frequencies.
|Example audiogram showing noise induced notch.|
Noise can also cause a reversible hearing loss, called a temporary threshold shift. This typically occurs in individuals who are exposed to gunfire or firecrackers, and hear ringing in their ears after the event (tinnitus). Non-occupational noise are also regularly encountered during recreational activities and are a source of premature hearing reduction. Peak noise levels, in DB, are provided in the following table taken from Smith et al, 1999).
Hearing loss and tinnitus (usually temporary), can also be associated with high doses of aspirin or other ototoxic drugs such as the nonsteroidal anti-inflammatory drugs.
Musical instruments can generate considerable sound and thus can also cause hearing loss. The most damaging type of sounds is in the high-frequencies. Violins and violas can be sufficiently loud to cause permanent hearing loss. This is typically worse in the left ear which is nearer the instrument. Unlike other instruments, the ability to hear the high-frequency harmonics is crucial to these musicians. Mutes can be used while practicing to reduce long term exposure.
There are a number of strategies that can be used to reduce the change of noise injury from other instrumentalists. Musicians ear plugs are generally "flat" so that bass and treble notes are not relatively favored, thus distorting perception. Nevertheless, a"vented" ear plug can be used to tune the ear cavity to low frequencies, which are less damaging. Drummers should use musicians ear plugs, such as the ER-25. Guitarists and vocalists can use the less attenuating ER-15. Too much ear protection can result in overplaying and not enough protection can result in hearing loss.
Plexiglass baffles can be used to reduce the noise from other instruments.These are particularly relevent for drummer's high-hat cymbals. Drums and brass can be particularly a problem. Ear monitors are small in-the-ear devices that look like hearing aids, that can be used to electronically protect hearing, while allowing the musicians to hear themselves. Acoustic monitors are stethescope like devices that block sound from other in the group, but allow the instrumentalist to hear their own instrument.
Loudspeakers produce both high and low frequency sounds. High frequencies tend to emanate in almost a straight line, while low frequencies are present in nearly all directions. Thus, standing besides a high-frequency source may provide some protection. Humming just prior to, and through a loud noise such as a cymbal crash or rim shot may provide some protection. Small protective muscles in the ear contract naturally when we sing or hum, and thus humming may protect from other noises.
(Most of this material comes from two articles by Chasin M, 2000. According to his articles, Mr. Chasin has published a book entitled "musicians and the prevention of hearing loss", which is available from Singular Publishing group, San Diego).
There are also many inherited causes of hearing loss. Treatments are mainly aimed at preventing further damage and making do with what is left. If the loss is minor, then avoidance of noise and ototoxic medications may be an appropriate "treatment". If the loss is significant, then a trial of a hearing aid is often worthwhile. Occasionally, persons with acquired deafness can be treated surgically with a surgically implanted device, a cochlear implant.
Tumors: While very unusual, acoustic neuromas or metastatic cancer (particularly breast) can be a source of hearing loss. Typically there is a combination of a hearing problem or either dizziness or imbalance. Audiometry, as below, generally shows an asymetrical sensorineural hearing loss.
Sudden hearing loss (SHL) is defined as greater than 30 DB hearing reduction, over at least three contiguous frequencies, occuring over 72 hours or less. It occurs most frequently in the 30-60 year age group. Differential diagnosis includes viral disease, vascular disease (1%), autoimmune phenomena, perilymph fistulae and Meniere's disease, and acoustic neuroma (about 4-6% of SHL -- see Daniels et al, 2000 for a longer list of diagnoses). Although some hold that this disease is generally idiopathic (i.e. of unknown cause), viral disease appears to be the basis for about 60% of all cases of SHL. Although called sudden, it seems unlikely that hearing loss is abrupt but rather it probably evolves over a few hours. Viruses detected at a study at the Massachusetts Eye/Ear infirmary included influenza type B, CMV, mumps, rubeola, and varicella-zoster (Harris, 1998). Evaluation usually begins with a careful history looking for potential infectious causes such as otitis media and exposure to known ototoxic medications. The natural history is recovery. Mattox and Simmons (1977) reported a rate of 65% spontaneous recover to "functional hearing levels". Byl also reported a recovery rate of about 69% (Byl, 1984). Because hearing tends to recover spontaneously at such a high rate, treatment is not always felt necessary, especially when impairment is minor.
Treatment of SHL, nevertheless, conventionally includes a burst of steroids such as prednisone. Eisenman and Arts recently reviewed the topic of steroid treatment(2000). Evidence to date, is mixed. Some studies suggest a better hearing prognosis for treated vs. untreated patients (Haberkamp and Tanyeri, 1999; Alexiou et al, 2001), some no difference (Kitajiri et al, 2002), and others a worse prognosis (Minoda et al, 2000). In the study of Alexiou et al, a better prognosis was associated with very high doses of intravenous prednisolone. Gianoli has recently reported a good response to transtympanic steroids, in persons who were unable to tolerate oral steroids (Gianoli, 2001). Fattori et al (2001) suggested that hyperbaric oxygen therapy was the treatment of choice. This involved 10, 90 minute sessions of breathing pure oxygen at 2.2 atmospheric pressure in a multiperson chamber. While encouraging, is is difficult to see why this treatment should work and we would like to see this result confirmed with other studies.
Antivirals would seem reasonable but unfortunately, acyclovir treatment seems unlikely to be helpful when the cause is a virus that is not in the herpes family, and one rarely knows at the time of the hearing loss which if any virus is responsible. In a recent animal study, combination treatment with an antiviral (acylovir) and steroids reduced damage in animals whose ears were innoculated with HSV-1 (Stokroos, 1999), compared to treatment with either acyclovir or prednisolone alone.
Haberkamp and Tanyeri recently reviewed the management of idiopathic SHL (Haberkamp and Tanyeri, 1999). They note that while numerous treatments have been studied aiming to improve blood flow, such as Carbogen inhalation or stellate ganglion block, all remain controversial or simply lack convincing evidence of efficacy. Very few placebo controlled studies have performed of treatment of SHL and for this reason, there is presently a limited ability to determine what is the optimal treatment of SHL.
References for Sudden Hearing Loss:
Presbyacusis is defined as hearing loss associated with degenerative changes of aging. There are four types: sensory presbyacusis is caused by loss of sensory elements in the basal end (high-frequency end) of the cochlea with preservation of neurons. These patients have symmetrical, high-frequency sensorineural hearing loss (as shown below). Pathology shows loss of hair cells. Neural presbyacusis is caused by loss of cochlear neurons. These patients have poorer discrimination than patients with sensory presbyacusis. Striatal presbyacusis is caused by loss of the stria vascularis with aging. Patients have a flat or slightly sloping hearing loss with good speech discrimination. Mixed presbyacusis is also possible. A final type is cochlear conductive presbyacusis. This is a sensorineural hearing loss caused by thickening of the basilar membrane caused by deposition of basophilic substance. This diagnosis is made on postmortem. (Harris, 1998). An example of presbyacusis is shown below. More information about presbyacusis is found here.
In conductive hearing loss, the second most common form of hearing loss, sound is not transmitted into inner ear. Diagnosis is ordinarily made via observation of an "air-bone gap" on audiometry, meaning that hearing is superior when sound is transmitted in such a way that it bypasses the middle ear ossicular chain.
Characteristically, hearing aids work well for this population. Causes include a buildup of ear wax, a foreign body in the ear canal, otosclerosis, typanosclerosis (as shown above), external or middle ear infections (otitis externa or media), allergy with serous otitis media, trauma to the ossicular chain such as temporal bone fracture, tumors of the middle ear, erosion of the ossicular chain (cholesteatoma) and perforation of the tympanic membrane.
Central deafness is extremely rare compared to conductive and sensorineural. A discussion of central deafness is found here.
Images marked as copyright Northwestern University were developed with the support of an NIH grant to Northwestern University Dept. of Otolaryngology, and are used with permission.