Definition

Hearing loss is a decreased ability to hear. There are two main categories of hearing loss:

Conductive hearing loss—due to something interfering with the sound passing to the inner ear.

Sensorineural hearing loss—due to damage to:

• The major organ in the ear responsible for hearing (the cochlea).
• The major nerve pathway (8th cranial nerve) and/or area of the brain responsible for hearing.

	The Anatomy of the Ear
	© 2008 Nucleus Medical Art, Inc.

Causes

Causes of conductive hearing loss include:

• Impacted ear wax
• Fluid in the middle ear
• Ear infections
• Perforation of ear drum
• Stiff bones in the middle ear ( otosclerosis )
• Injury
• Loose or fractured bones in the middle ear
• Missing bones from the middle ear due to previous surgery
• Congenital anomaly causing complete closure of the ear canal (Atresia)
• Tumors

Causes of sensorineural hearing loss include:

• Excess noise
• Aging
• Family history
• Exposure to toxic substances, including such drugs as:
  • Streptomycin
  • Gentamicin
  • Chemotherapy drugs
  • Diuretics
  • Steroids
  • Heart medicines
  • Anesthetics
  • Quinine
  • Aspirin-containing drugs
• Acoustic neuroma
• Cardiovascular disease
• Multiple sclerosis
• Viruses ( measles , mumps , adenovirus, rubella )
• History of meningitis or syphilis
• Neurologic diseases such as multiple sclerosis and stroke
• Inner ear disorders such as Meniere’s disease
• Otosclerosis affecting the inner ear
• Previous brain or ear surgery causing damage to the inner ear
• Trauma

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition.

Risk factors for hearing loss include:

• Family history
• Aging
• Meniere's disease
• Not receiving all recommended immunizations
• Repeated or poorly treated ear infections
• Exposure to loud noise, music, or machinery
• Use of certain antibiotics and chemotherapy drugs
• Diseases that may result in blocked blood flow, including atherosclerosis , problems with blood clots, and collagen vascular diseases

Symptoms

Symptoms may include:

• Decreased ability to hear any of the following:
  • Higher pitched sounds
  • Lower pitched sounds
  • All sounds
  • Speech when there is background noise
• Dizziness
• Ringing sounds in the ears
• Problems with balance
• In children, hearing loss may cause difficulty learning to speak.

Diagnosis

The doctor will ask about your symptoms and medical history, and perform a physical exam. Tests may include:

• Weber test—a tuning fork is sounded and placed on your forehead or teeth. This can help distinguish conductive from sensorineural hearing loss.
• Rinne test—a tuning fork is sounded and placed in front and then behind of the ear. This can help distinguish conductive from sensorineural hearing loss.
• Audiometric tests—these involve listening to tones in a soundproof room, and reporting whether or not you hear the tones.
• Tympanometry—this test measures the pressure in the middle ear and examines the middle ear's response to pressure waves.
• CT or MRI scan of the head —a type of imaging study that uses a computer to make pictures of the inside of the head. This may be done to check for a tumor or bone injury.
• Brain stem auditory evoked responses—in this test, electrodes are attached to the scalp and used to measure the electrical response of the brain to sound.
• Electrocochleography—this tests the cochlea and the auditory nerve.

Treatment

Treatment includes:

Earwax Removal

This is probably the simplest, easiest treatment for hearing loss.

Hearing Aids

There are many types. Digital technology has created tiny devices that cause little distortion.

Devices

One example of a device is the FM trainer. With this device, a person speaks into a microphone. The sound is then transmitted by radio waves directly to the earphone set worn on your ear. This can be particularly helpful if you have trouble hearing speech when there is background noise. FM trainers can also help children with hearing loss to understand their teachers.

Cochlear Implant

This device is surgically implanted. It directly stimulates part of the brain and uses a tiny computer microprocessor to sort out incoming sound.

Treat Other Medical Illnesses

When hearing loss is caused by other medical conditions, it may be possible to improve hearing by treating those conditions.

Discontinue or Change Medications

If your hearing loss may be caused or worsened by a medication, talk to your doctor about stopping that particular drug, or changing to a drug that doesn't affect hearing.

Address Nutritional Deficiencies

It may be possible to slow age-related hearing loss in elderly persons through dietary modification. In a recent study, 728 men and women with age-related hearing loss and low folic acid levels in their blood were given either folic acid supplements (800 µg) or placebo for three years. Hearing decline for speech was slower in the group that received folic acid during that period of time. *

Surgery

Surgery may be done in some cases of conductive hearing loss to correct the middle ear problem, such as in otosclerosis , ossicular damage or fixation, and ear infections.

Prevention

To help prevent hearing loss:

• Stop smoking.
• Adequately treat ear infections.
• Get all appropriate immunizations.
• Treat all medical conditions.
• Avoid exposure to excess noise.
• Use adequate ear protection when using noisy equipment.

RESOURCES:

American Academy of Otolaryngology–Head and Neck Surgery, Inc.
http://www.entnet.org

American Speech-Language-Hearing Association
http://www.asha.org

CANADIAN RESOURCES

Health Canada
http://www.hc-sc.gc.ca

Society of Rural Physicians of Canada
http://www.srpc.ca

References:

Current Medical Diagnosis and Treatment . Lange Medical Books; 2001.

Family Practice Sourcebook . Mosby; 2000.

Ferri's Clinical Advisor . Mosby; 2000.

The Little Black Book of Primary Care . Blackwell Science; 1999.

M. C. Hansen. Otosclerosis and sensorineural hearing loss. A clinical study. Archives of Otolaryngology Head and Neck Surgery . Vol. 109 No. 9, September 1983

Sang Heun Lee, Yongmin Chang, Ji Eun Lee, Jin-Ho Cho : The values of diffusion tensor imaging and functional MRI in evaluating profound sensorineural hearing loss. Cochlear Implants International. Volume 5, Issue S1 , Pages 149 - 152.

Updated Treatment section on 1/24/2007 according to the following studies, as cited by DynaMed's Systematic Literature Surveillance : Durga J, Verhoef P, Anteunis L, Schouten E, Kok F. Effects of folic acid supplementation on hearing in older adults: a randomized, controlled trial. Ann Int Med. 2007;146(1):1-9.

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