Hearing loss: an overview

The term “sensorineural” is used here to describe the hearing loss that is believed to be the result of a physiologic malfunction in the inner ear or acoustic nerve. The “sensory” component of the hearing loss conceptually correlates with malfunction in the organ of Corti, likely within the hair cells, and becomes manifest when elevated puretone thresholds are seen on an audiogram. The neural component conceptually correlates with malfunction within or proximate to the acoustic nerve and is recognizable when a patient has poor word discrimination when tested by an audiologist. For example, if a patient with moderate sensorineural hearing loss based on puretone scores has excellent word discrimination scores, this suggests that the locus of the problem is more within the inner ear than in the acoustic nerve or in the brain. For a patient who has a mild to moderate sensorineural hearing loss along with poor word discrimination, however, this suggests that the patient might have problems both within the inner ear and also perhaps within the acoustic nerve, and possibly the patient may also be experiencing difficulty with brain function. In general, people with hearing impairment mostly confined to the inner ear do well with amplification and hearing aids, whereas those who have impaired function of the acoustic nerve and impaired brain function typically have more difficulty using hearing aids.

Sensorineural hearing loss can vary with respect to onset and severity, and can affect one or both ears. The onset of the hearing loss is typically defined as prelingual if it manifests before speech-language acquisition and defined as postlingual if is known to have occurred after speech development. It should be noted that all congenital hearing loss is prelingual but not all prelingual hearing loss is congenital. Hearing loss that develops after birth is generally referred to as “acquired” hearing loss. Congenital hearing loss usually is the result of a prenatal infection, such as rubella, toxoplasmosis, cytomegalovirus, or herpes, or the hearing loss can be inherited as a result of a gene mutation. Acquired hearing loss in children might be caused by meningitis or some injury to the inner ear including the effect of receiving ototoxic medication. Acquired hearing loss in adults is usually attributed to noise exposure, trauma, ototoxic drugs, presbycusis, or Meniere’s disease. Some adults develop sudden hearing loss with no apparent cause, and this is described as sudden idiopathic sensorineural hearing loss. Hearing loss usually is bilateral and symmetrical; however, in the case of Meniere’s disease and sudden sensorineural hearing loss, the disease process may produce a unilateral hearing loss. Often in the case of unilateral hearing loss, the patient may experience the feeling of being off balance and lack the ability correctly to localize sound. Frequently, patients who have an acquired unilateral hearing loss are faced with the unknown in regards to the other ear. Many times, their first question is if they will develop a hearing loss in the other ear. Counseling and palliative care are essential in caring for and treating these patients.

Sensorineural hearing loss can develop then progress over time, and is seen commonly in genetic- and syndrome-associated hearing loss, presbycusis, autoimmune inner ear disease, and Meniere’s disease. Approximately 70% of genetic hearing loss is nonsyndromic, whereas the remaining 30% is considered to be syndromic because it is associated with findings that can be detected on physical examination. Over 400 genetic syndromes that include hearing loss have been described. Syndromic hearing loss constitutes approximately 30% of prelingual deafness; however, its overall contribution to all hearing loss is much smaller, reflecting the occurrence and diagnosis of postlingual and often progressive hearing loss (Stickler’s syndrome, Usher syndrome, Alport’s syndrome). Presbycusis is hearing loss related to aging and is typically associated with high-frequency hearing loss and compromised speech intelligibility. Patients report that they can hear what people are saying but they are having a difficult time understanding what is being said. Many patients with presbycusis benefit from amplification and successfully use hearing aids. The hearing loss associated with autoimmune inner ear disease and Meniere’s disease, however, tends to fluctuate and worsen over time. Autoimmune inner ear disease is difficult to diagnose because there really is no single reliable laboratory test to confirm the diagnosis. In general, a hearing loss that occurs relatively rapidly in one or both ears especially in young or middle aged adults potentially could be autoimmune inner ear disease. If the hearing improves with steroid medication given orally, then this further suggests an autoimmune etiology. When patients have repeatedly had hearing improvement while on steroids and then decrement in hearing after cessation of the steroid medication, then low-dose methotrexate therapy can be considered for long-term management instead of leaving the patient on the steroid. Unfortunately, despite medical treatment, patients with autoimmune inner ear disease can have progressive hearing loss leading to deafness. Because there is no treatment that can reliably restore hearing or maintain improved hearing long-term, the management of autoimmune inner ear disease is palliative, not curative. Patients with autoimmune inner ear disease usually have lived most of their lives with normal hearing and they become quite upset when they realize that they have a condition that can result in severe hearing impairment perhaps jeopardizing their employment and creating, for them, major communication problems.

Effects of hearing loss

Hearing loss affects not only the patient, but also loved ones and anyone whom the patient must communicate with in daily life. In general, younger patients with difficulty hearing often experience frustration, depression, and anxiety related to the loss of hearing. More elderly patients with presbycusis tend to view the hearing loss as part of the process of aging, and they seem to accept the hearing loss as just something that happens and can be accepted. Interestingly, not all patients who have hearing impairment are eager to obtain a hearing aid. Some patients say that amplification does not work because one of their friends had a bad experience with a hearing aid, or say that they cannot afford to purchase a hearing aid because most insurance companies do not reimburse for the costs of hearing aids. When a loved one or family member has hearing impairment severe enough to affect conversation but the patient is reluctant to obtain a hearing aid, then this can cause frustration within the family.

Much like the well known stages of accepting that an illness is terminal and incurable, patients diagnosed with presbysusis or progressive hearing loss can go through stages of acceptance of their disability analogous to the Kübler-Ross stages of death and dying ( Box 1 ).

The stages shown in the box below describe the emotions of individuals dealing with grief and loss. They were originally applied to those who experienced catastrophic personal loss; however, others have applied them to considerable personal changes. Kübler-Ross stated that the stages do not necessarily occur in this order, nor are they experienced by all persons; however, individuals tend to experience at least two of the stages.

When a child is born deaf, then the parents go through an adjustment period, first perhaps being in denial and then finally accepting that their child will be unable to hear normally and perhaps become optimistic that a cochlear implant will help their child to live a near normal life. During the stage of denial, parents confronted with results of a follow-up newborn hearing test indicating significant hearing impairment may question the accuracy of the test because they believe their child is responding to his or her name or the child can hear sounds in the home. Ultimately, parents are able to accept the reality that they have a hearing impaired child. The roles of the physician and audiologist in working with the parents of a hearing impaired child are to be supportive, to listen to the concerns of the parents, and to assist the parents in deciding what choices to make among the many alternatives for management of the child’s hearing impairment. Parents need to be guided through the process of pursuing and obtaining the appropriate accommodations, such as hearing and speech evaluations and individualized education plans. As parents cope with the stress of realizing and accepting that they have a hearing impaired child, making the difficult choices needed how best to be of help to their child, puts considerable stress on the entire family. Although hearing impairment can be helped but not cured, the well-being of the affected child and the involved family depends greatly on a team of involved professionals including an otolaryngologist or otologist, an audiologist, and a speech-language pathologist who are able to be supportive, listen to the concerns being expressed, and provide guidance.

In contrast to the situation surrounding the birth of a hearing impaired child, when a young patient develops hearing loss that was not present at birth there is a tendency for the affected patient to experience grief related to the loss of hearing. That is, the child or young adult who is experiencing loss of hearing after having previously had normal hearing must cope with a major change in self-image and daunting challenges in ability to perform daily activities. The management of a child or young adult with progressive sensorineural hearing loss can be one of the most frustrating aspects of practicing otolaryngology because explaining the cause of such hearing loss is difficult and there is so little that can be done medically or surgically to restore hearing or even to avert further hearing loss. Consequently, otolaryngologists and audiologists managing the patient need to be supportive and optimistic about the ultimate outcome for the patient without providing misleading information that can give the patients and parents false hope. In past decades, parents of children and young adults who were experiencing progressive sensorineural hearing loss were told that the hearing loss might be caused by a perilymph fistula and exploration of the middle ear, with repair of the fistula if found, could restore hearing or prevent further loss of hearing. During that bygone era in otology, too many parents were given false hopes about the benefits of a simple surgical procedure and too many youngsters had surgical procedures that probably were not needed or even helpful. Fortunately, that era in the management of progressive sensorineural hearing loss has ended and it is now known that the palliative care for patients with progressive hearing loss mostly involves emotional support, genetic testing, discussions about amplification with hearing aids, and cochlear implants, not talk of quick operations with little proved benefit. Information helpful in having rational and reasonable discussions with families about the kinds of hearing loss that cannot be corrected with middle ear surgery is discussed next.