Hearing Loss and Ototoxicity

1

What should the history include when evaluating hearing loss?

When evaluating any type of hearing loss, it is important to ask about laterality, duration, progression, current severity, associated factors (such as otalgia, otorrhea, tinnitus, vertigo, and aural fullness), ototoxic medication use, head trauma, family history (to assess for genetic factors), autoimmune disease, and prior otologic surgery.

2

What should the physical exam include when evaluating a patient with hearing loss?

A complete head and neck exam should be performed, with a focus on otologic and neurologic exams. The otologic exam should include examination of the pinna, external auditory canal, tympanic membrane, and middle ear. Tuning fork tests (Weber and Rinne) and pneumatic otoscopy should also be routinely performed.

3

How can you differentiate between SNHL and CHL on an audiogram?

The two main ways to differentiate between SNHL and CHL on an audiogram include the presence of an air–bone gap and abnormal tympanogram. An air–bone gap ( Fig. 34.1 ) is present during conductive or mixed (both SNHL and CHL) hearing losses and is caused by differences in air-conducted and bone-conducted stimuli. During the vibratory portion of the audiogram, a patient with CHL will be better able to hear the stimulus because the transmission of sound through the mastoid bone is bypassing the site of blockage in the external or middle ear.

The tympanogram measures the compliance of the tympanic membrane. Increased compliance (type A _d ) can indicate ossicular chain discontinuity, whereas decreased compliance (type A _s ) can indicate otosclerosis, both of which can cause conductive hearing loss. Poor compliance (type B) on a tympanogram can indicate a tympanic membrane perforation or middle ear effusion.

4

What are the common causes of SNHL?

The most common causes of SNHL are presbycusis, noise exposure (i.e., machinery, artillery, loud music), and heredity. Less common causes are acoustic trauma, ototoxicity, sudden idiopathic hearing loss, autoimmune hearing loss, Meniere’s disease, tumors, and infections (i.e., meningitis, viral labyrinthitis).

5

What is presbycusis?

Presbycusis is age-related hearing loss. This is the most common type of hearing loss in adults, encompassing the great majority of adult-onset hearing loss. Presbycusis is bilateral, symmetric, and slowly progressive high-frequency loss. Onset is in adults over 60 years of age, and the exact cause is unknown. Hearing aids are the most effective treatment.

6

What guidelines are in place for newborn hearing screening?

The US federal government mandates newborn hearing screening, although programs are state regulated. The most commonly used is the otoacoustic emissions test, which examines the outer hair cell response to acoustic stimulation. The other common test is the auditory brainstem response test, in which the eighth nerve and central nervous system produce sounds in response to acoustic stimulation. In either case, if the results are abnormal, the newborn is referred for further testing.

7

What is the incidence of congenital hearing loss?

One to three infants per 1000.

8

What risk factors predispose children to hearing loss?

Risk factors that have been correlated with congenital hearing loss are (per the Joint Committee on Infant Hearing):

• Family history of childhood onset permanent hearing loss

• In utero infections (ToRCH = toxoplasmosis, other [syphilis, parvovirus, varicella], rubella, cytomegalovirus, herpes)

• Illness requiring Neonatal Intensive Care Unit admission for more than 48 hours

• Craniofacial anomalies, especially involving the pinna or external auditory canal

• Characteristic signs of syndromes known to cause hearing loss

Other factors associated with increased rates of congenital hearing loss in the literature:

• Low birth weight (less than 1500 g)

• Hypoxia

• Hyperbilirubinemia

• Low Apgar scores

• Head trauma

• Ototoxic medications

9

What are the developmental milestones for pediatric speech and hearing?

• 0 to 3 months: startled by loud sounds, calmed by familiar voices

• 6 months: localize sounds

• 9 months: respond to name and can mimic sounds

• 12 months: say first words

• 18 months: can follow simple commands

• 2 years: say 20 or more words and put together two-word sentences