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Related to conduction deafness: nerve deafness, tone deafness, sensorineural deafness, transmission deafness
Hearing impairment has multiple causes. Congenital deafness occurs during pregnancy or delivery and in such syndromes as neurofibromatosis or Usher syndrome. Toxic deafness may result from exposure to such agents as salicylates, diuretics, or aminoglycoside antibiotics, or infections of the central nervous system (meningococcal meningitis, syphilis) or of the eighth cranial nerve. Many viruses may contribute to loss of hearing, as may prolonged or repetitive exposures to environmental noise. Otosclerosis is an example of bilateral conductive hearing loss due to progressive ossification of the annular ligaments of the ear. Presbycusis is an otologic effect of aging resulting from the loss of hair cells in the organ of Corti and leading to progressive, symmetrical, bilateral sensorineural hearing loss, esp. of high-frequency tones. Sudden hearing loss may result from ear trauma, fistulae, stroke, drug exposures, cancer, multiple sclerosis, vasculitis, or Ménière disease. Not infrequently, adult patients with unilateral conductive hearing loss have a cerumen impaction.
Simple bedside tests (such as assessing a patient's ability to hear a whispered phrase or the sound of rasping fingers) may suggest hearing impairment. Tuning fork tests that compare air and bone conduction of sound help clinicians identify whether hearing loss is due to conductive or sensorineural causes. Audiometry provides definitive diagnosis.
The degree of hearing loss is calculated according to an American Medical Association formula: For every decibel that the pure tone average exceeds 25 dB, hearing impairment equals 1.5%. Therapy depends on the underlying condition. Cerumen impaction, for example, responds to irrigation of the external auditory canal, while otosclerosis may respond to the intra-aural (surgical) placement of prostheses or laser surgery. Other forms of therapy include the use of hearing amplifiers or cochlear implants or education in lip reading or sign language.
Patients can prevent damage to hearing from excessively loud noises by wearing sound-muffling ear plugs or muffs when exposed to loud noise from any source, esp. industrial noise, and by recognizing that loud music can be as detrimental to hearing as the noise of a jackhammer. After exposure to noise levels above 90 dB for several hours, overnight rest will usually restore normal hearing, but not in those who experience repeated exposure. Patients should avoid cleaning inside the ears or putting sharp objects in them. Many antibiotics and chemotherapeutic drugs are ototoxic and hearing should be evaluated continually when such drugs are used.
When interacting with a person with a hearing deficit, the health care professional should make his or her presence known to the patient by sight by raising or waving of the arm (as even gentle touch may startle the person) before beginning to speak. If possible, background noise should be decreased. The health care professional's face should be well lit to make the lips and facial expression easy to see. He or she should face the patient directly or direct the voice toward the side preferred by the patient. To facilitate lip reading, short words and simple sentences should be used. Clear and distinct enunciation and speaking slowly in a low tone are helpful. Exaggerated mouthing of words or loud tones and shouting should be avoided. Placing a stethoscope in the patient's ears and speaking into the bell helps to limit extraneous sounds and to direct words into the patient's ears. If the patient is literate, sign language or finger spelling may be used to communicate. Written information should be presented clearly and in large letters, esp. if the patient has poor visual acuity.
Any child in whom hearing loss is suspected or who fails a language screening examination should be referred to an audiologist or otolaryngologist for further evaluation and therapy and, as necessary, to a speech therapist for language evaluation and therapy.
Health care professionals can help prevent hearing loss in their patients and communities by teaching about and assessing for signs of hearing impairment in anyone receiving ototoxic drugs; stressing the dangers of excessive noise exposure; explaining to pregnant women the danger to the fetus from exposure to drugs, chemicals, and infections, esp. rubella; and encouraging the use of protective devices in noisy environments and during occupational or recreational exposure to noise.