Causes of hearing loss

It is normal as a parent to need to know why your child has a hearing loss. Sometimes the cause of hearing loss can be determined and sometimes it cannot. 25% of infant hearing losses are due to unknown causes. Sometimes the hearing loss is caused by a combination of factors. A physician will guide you through the process to determine the cause of your baby’s hearing loss. The process begins by the physician reviewing your family history, your baby’s birth history, and an examination of your child. The physician may order medical and lab testing to help determine the cause.

Permanent childhood hearing loss can be congenital, delayed-onset, progressive, or acquired. Hearing loss from birth, referred to as congenital hearing loss, is often identified through a newborn hearing screening. Some hearing loss in childhood is delayed-onset or progressive in nature. As a result, it is important to monitor hearing over time for children who are considered to be at risk for hearing loss.

  1. Acquired Hearing Loss

Acquired hearing loss occurs after birth. Conditions that may cause permanent acquired hearing loss in children include ototoxic medications, encephalitis, mumps, measles, meningitis, large vestibular aqueduct, head injury, and noise exposure.

  • Genetic Factors

Genetic factors make up about 50% of infant hearing loss. A genetic factor can be inherited or non-inherited and refers to the “code” that determines the unique characteristics of a child. Hearing loss from genetic causes can be congenital or develop later in life. The two types of genetic hearing loss are nonsyndromic hearing loss and syndromic hearing loss. A nonsyndromic hearing loss means that the hearing loss occurs without involvement of other systems in the body. Connexin 26 is the most common type of nonsyndromic genetic hearing loss. A syndromic hearing loss means that the hearing loss is in addition to a recognized set of characteristics. About 20% of genetic hearing losses are related to syndromes. Examples of genetic disorders that include hearing loss are Down syndrome, Usher syndrome, Treacher Collins syndrome, Crouzon syndrome, Alport syndrome, Sickle cell disease, Tay-Sachs disease, Waardenburg syndrome, Pendred syndrome, Goldenhar syndrome, and CHARGE syndrome.

  • Nongenetic Factors

25% of infant hearing losses are non-genetic. Permanent hearing loss that is non-genetic can be a result of maternal infections (e.g., rubella, cytomegalovirus, herpes simplex virus, syphilis, toxoplasmosis, chickenpox), prematurity, low birth weight, lack of oxygen (anoxia), hyperbilirubinemia, maternal diabetes, toxins such as drugs and alcohol consumed by the mother during pregnancy, or inner ear malformations (e.g., Mondini’s malformation, large vestibular aqueduct).

  • Large Vestibular Aqueduct Syndrome

Large vestibular aqueduct (LVA), a congenital enlargement of the cochlear aqueduct, is the most common malformation of the inner ear associated with sensorineural hearing loss. This condition is referred to as large vestibular aqueduct syndrome (LVAS). The vestibular aqueduct is the bony canal that travels from the vestibule into the temporal bone. Inside the vestibular aqueduct is a tube known as the endolymphatic duct that carries endolymph fluid from the inner ear to the endolymphatic sac. When the vestibular aqueduct is enlarged, the endolymphatic sac and duct enlarge to fill the space. It is thought that the endolymphatic sac and duct help regulate the concentration of ions in the cochlear fluids and this enlargement may result in a chemical imbalance, disrupting the transmission of hearing and balance nerve signals to the brain. LVA can result from abnormal or delayed development of the inner ear (non-syndromal) or may be associated with syndromes such as Pendred syndrome, brancio-oto-renal syndrome, CHARGE syndrome, or Waardenburg syndrome.

  • Cholesteatoma

Cholesteatoma is a tumor like growth in the middle ear. They are generally formed from the skin cells on the outside of the eardrum that have become folded into the middle ear as a result of ear infections or with a perforation of the eardrum. The squamous epithelium, or skin layer, of the outside of the eardrum is continuously replaced and the old skin elements are meant to come out through the ear canal. When these skin elements become trapped behind the eardrum in the middle ear or mastoid, it is called a cholesteatoma. Cholesteatoma typically grows very slowly and begins to cause symptoms as it compresses and erodes the structures of the middle ear and surrounding areas. Often the debris is infected with bacteria or other organisms, causing drainage and a foul smell.

Acquired cholesteatoma, the type that generally occur as a result of infection, is the most common type of cholesteatoma. This type of cholesteatoma may occur at any age. The other type of cholesteatoma is congenital cholesteatoma, which is much less common. In this type, skin cells are trapped in the middle ear from birth. These skin cells grow in the middle ear and have no way of coming out of the middle ear cavity because of the intact eardrum. The typical age of presentation for a congenital cholesteatoma is 4 to 6 years old.

  • Childhood Noise Exposure

One of the most common and yet completely preventable causes of permanent sensorineural hearing loss is exposure to sound levels that are excessively loud. High noise levels first cause temporary hearing loss and then permanent damage to the sensory hair cells within the cochlea. Even young children may be exposed to sounds that could be damaging to their hearing. Noise produced by various modes of transportation (airplanes, subways, trains) and home appliances (stereo speakers, power tools, lawn mowers, hair dryers) may be damaging to hearing depending upon the exposure time and distance to the noise source. Even some toys can produce intense sound and certainly sound levels at some music concerts can damage hearing.

Monitor the level of noise your child is exposed to. If speech must be raised to communicate, most likely the noise is excessive and possibly damaging. Ringing in the ears known as tinnitus after noise exposure indicates excessive sound levels. Children should be told about the dangers of noise exposure and the use of ear protection (ear plugs, ear muffs). Children should be protected from excessive noise exposure whenever possible.

Hearing Protection: As a parent, you can set examples for your child on hearing conservation. If hearing and the use of hearing protection are important to you, it will also be important to your child. When using power tools or mowing the lawn, use hearing protection and if your child is playing nearby, make him or her also use hearing protection. Using hearing protection will protect both your hearing and your child’s hearing.

SOME COMMON HEARING PROBLEMS IN CHILDREN

Children will experience one or some of the most common hearing problems with the most common being otitis media, a condition of the middle ear. Discussed below are some causes of common hearing problems.

  • Wax (Cerumen)

An excessive amount of wax in the ear canal can block sound waves from going to the eardrum. Wax softening drops can help the wax exit the canal. A physician can irrigate the canal or remove the wax. Parents should never use Cotton swabs in an attempt to remove wax. The cotton swab may actually push the wax deeper into the canal or damage the eardrum.

  • Foreign Objects

Foreign objects such as beads and food items impede sound and can damage the eardrum. The ear canal may become inflamed if the object damages the surface lining.

  • Swimmer’s Ear

Another common condition affecting the outer ear canal is called “swimmer’s ear.” This external ear canal infection may be painful and cause the ear canal to swell, resulting in temporary hearing loss. In most cases, it is a bacterial infection that develops in an ear canal that stays wet after bathing or swimming