32 Hearing Loss & Ototoxicity Flashcards
What is sensorineural hearing loss (SNHL)?
What is sensorineural hearing loss (SNHL)?
Sensorineural hearing loss is caused by inadequate sound processing by the end organ of hearing, the cochlea (sensory), or poor transmission by the eighth cranial nerve (neural ) to the central nervous system. The function of the cochlea is to convert sound energy into electrical impulses that are then transmitted to the auditory centers in the brain. In sensorineural hearing loss, this pathway is disrupted.
What is conductive hearing loss (CHL)?
What is conductive hearing loss (CHL)?
Conductive hearing loss is caused by impaired sound transmission to the inner ear. Abnormalities in the external canal, tympanic membrane, ossicles, and middle ear account for this type of hearing loss. The maximal amount of CHL is 60 decibels,
CHL over 50 decibels is most likely caused by ossicular chain pathology.
What should your history include when evaluating hearing loss?
What should your 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.
What should your physical exam include when evaluating a patient with hearing loss?
What should your physical exam include when evaluating a patient with hearing loss?
A complete head and neck exam should be performed, with a focus on the 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.
How can you differentiate between SNHL and CHL on an audiogram?
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
- abnormal tympanogram.
An air–bone gap 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 Ad) can indicate ossicular chain discontinuity, whereas decreased compliance (type As) can indicate otosclerosis, both of which can cause a conductive hearing loss. Poor compliance (type B) on a tympanogram can indicate a tympanic membrane perforation or middle ear effusion.
What are the common causes of SNHL?
What are the common causes of SNHL?
The most common causes are:
- Presbycusis
- Noise exposure (i.e., machinery, artillery, loud music)
- 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).
What is presbycusis?
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, slowly progressive high-frequency loss. Onset is in adults over 60 years, and the exact cause is unknown. Hearing aids are the most effective treatment.
What guidelines are in place for newborn hearing screening?
What guidelines are in place for newborn hearing screening?
The U.S. federal government mandates newborn hearing screening, but programs are state regulated. The most commonly used test is otoacoustic emissions (OAE), which tests the outer hair cell response to acoustic stimulation. The other common test is auditory brainstem response (ABR), in which the eighth nerve and central nervous system produce sounds in response to an acoustic stimulation. In either case, if the test is abnormal, the newborn is referred for further testing.
What is the incidence of congenital hearing loss?
What is the incidence of congenital hearing loss?
One to three infants per 1000.
What risk factors predispose children to hearing loss?
What risk factors predispose children to hearing loss?
Risk factors that have been correlated with congenital hearing loss are (per 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 NICU 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 grams)
- Hypoxia
- Hyperbilirubinemia
- Low APGAR scores
- Head trauma
- Ototoxic medications
What are the developmental milestones for pediatric speech and hearing?
What are the developmental milestones for pediatric speech and hearing?
- 0 to 3 months: startled by loud sounds, calmed by familiar voice
- 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 2-word sentences
When should SNHL be evaluated with imaging?
When should SNHL be evaluated with imaging?
- In children, MRIs or CT scans of the temporal bones are usually performed for all SNHL, although the majority of these scans will be normal. The most common finding in pediatric SNHL is enlarged vestibular aqueduct.
- In adults, MRI of the IACs with contrast is performed for asymmetric* SNHL or *sudden SNHL to evaluate for acoustic neuroma (Figure 32-2) and other cerebellopontine angle tumors.
What medications can cause ototoxicity?
What medications can cause ototoxicity?
- Antibiotics (specifically aminoglycosides and vancomycin)
- Chemotherapy drugs (cisplatin)
- Loop diuretics (furosemide, ethacrynic acid)
- NSAIDs and salicylates (aspirin)
How do ototoxic medications cause hearing loss?
How do ototoxic medications cause hearing loss?
Aminoglycosides damage both vestibular and cochlear hair cells.
- Streptomycin & Gentamycin: vestibular > hearing
- Neomycin & Tobramycin: hearing > vestibular
- Vancomycin potentiates the ototoxic effect of aminoglycosides, but does not appear to be ototoxic alone.
- Cisplatin damages outer hair cells.
- Loop diuretics damage the stria vascularis (which maintains the endocochlear potential).
- NSAIDs & Salicylates cause damage to the cochlea, only occurring with high doses, which is almost always completely reversible with discontinuation of the drug.
Since most ototoxic medications are excreted by the renal system, renal impairment can lead to higher rates of ototoxicity.
How does ototoxicity present?
How does ototoxicity present?
The first symptom is usually (1) tinnitus, followed by (2) perception of hearing loss. Hearing loss is usually symmetric and affects the high frequencies first. With continued exposure, the lower frequencies are affected.
The American Academy of Audiology recommends ototoxicity audiology protocols that include pure tone and DPOAE (a type of otoacoustic emission) testing at ultra-high frequencies (8 kHz to 20 kHz) because the earliest changes occur at frequencies greater than 8 kHz.
What is otosclerosis?
What is otosclerosis?
Otosclerosis is fixation of the stapes footplate in the oval window caused by abnormal remodeling of bone in this area. Otosclerosis causes either unilateral or bilateral conductive hearing loss that can have a Carhart notch pattern (artificial 10 to 15 decibel decrease in bone conduction at 2000 Hz). Many cases of otosclerosis are hereditary. Treatment includes either stapedectomy* or a *hearing aid.
