Hearing Loss

Question 1

What are the main structures of the outer ear?

Answer 1

• consists of the pinna and ear canal (cartilaginous + bony)
• terminates at ear drum
• external ear is formed of helix, anti-helix, tragus, anti-tragus + lobule
• lobule is non-cartilaginous
• ear canal - the outer 1/3 is fibrocartilaginous + produces ceremen and the remainder is bony

Question 2

What are the main structures of the middle ear?

Answer 2

• region of the ear from tympanic membrane, extending to just externally to oval window
• functions to transfer energy from compression waves in air to fluid membrane waves within cochlear
• formed of ossicle → malleus, incus, stapes
• muscles → stapedius innervated by CN VII + tensor tympani (CN V) contract in response to loud sound, protecting inner ear (tympanic reflex)

Question 3

What are the main structures of the inner ear?

Answer 3

• semicircular canals → for balance
• cochlea → for hearing
• cochlea present with hair cells helping to generate electrical signals for hearing, sent via auditory nerve

Question 4

How are sound waves transduced to nerve impulses?

Answer 4

• tympanic membrane converts waves of sound in air to pressure waves in the fluid of the inner ear
• displacement of the basilar membrane causes movement of hair cells
• generates action potentials → different bits of cochlea respond to different frequencies
• vestibulocochlear nerve sends impulses to the cortex where sound is perceived

Outer hair cells amplify sounds whereas inner hair cells transmit sounds

Question 5

What is the neurological pathway between the cochlea and the auditory cortex?

Answer 5

• the primary auditory pathway
• primary auditory cortex is located in the temporal area within the lateral sulcus

auditory nerve → cochlear nuclei (brainstem) → superior olivary complex (brainstem) → superior colliculus (mesencephalus) → medial geniculate body (thalamus) → auditory cortex

Question 6

What is the difference between sensorineural hearing loss, conductive hearing loss, and mixed hearing loss?

Answer 6

• sensorineural → stems from either cochlea (inner ear), the nerve that runs from cochlea to brain or a combination of both, sometimes termed ‘permanent’ hearing loss
• conductive → stems from fluid, tissue or bony growth that blocks or reduces incoming sound - can involve ear canal, middle ear, ear drum or bones in middle ear, often referred to as ‘temporary’ or ‘transient’
• mixed → both types present in same ear

Question 7

How do you do an otoscopy?

Answer 7

• seek consent
• use otoscope
• inspection → scars, shape, swellings, deformities, inflammation + skin conditions, hearing aids
• examination of pinna + adjacent features → neck, behind pinna, pinna
• palpate → mastoid, tragus, TMJ, pull ear up (pain suggests otitis externa)
• position → manipulate pinna to straighten ear canal
  
  • adults - upwards + backwards
  • young kids - backwards + sometimes also downwards
• look at tympanic membrane, assess systematically:
  
  • handle of malleus
  • assess for colour + light reflex (anteriorly + inferiorly)
  • work systemically around pars tensa
  • look at pars flaccida and attic

Question 8

Rinner’s and Weber’s are bedside tests to determine if it is a conductive or sensorineural deafness (if you don’t have access to audiometry). Must use a 512Hz tuning fork.

What is Rinne’s test?

Answer 8

• hold tuning fork adjacent to patient’s external acoustic meatus and then against mastoid process - “is it louder in front of behind?”
• if louder in front ie. AC > BC:
  
  • Rinne’s +ve = normal or mild/mod SNHL on that side
• if louder behind ie. AC < BC:
  
  • Rinne’s -ve = conductive hearing loss on that side OR severe/profound SNHL on that side

Question 9

What is Weber’s test?

Answer 9

• hold tuning fork against patient’s forehead in midline
• ask patient where they hear the sound
• ‘do you hear loudest in: left, right or both?’
• if it doesn’t lateralise → normal (or symmetrical mild/mod hearing loss)
• lateralises →
  
  • loudest in affected ear = conductive hearing loss
  • loudest in contralateral ear = SNHL

Question 10

What is pure tone audiometry?

Answer 10

• subjective test
• measures the quietest sounds a person can hear at different frequencies (pitch) in each ear separately
• results are plotted in a pure tone audiogram
• crosses = L ear, circles = R ear

Question 11

What are the classes of hearing loss on an audiogram?

Answer 11

Question 12

How do you describe audiograms?

Answer 12

• unilateral or bilateral hearing loss?
• if bilateral → symmetric or asymmetric?
• degree of hearing loss → mild, mod, severe or profound?
• type of hearing loss → conductive, sensorineural or mixed?
• configuration of hearing loss → flat, downward sloping, upward sloping, U shaped, notched, cookie bite, etc

Question 13

Describe this audiogram

Answer 13

Testing air conduction - normal in both ears

Question 14

Describe this audiogram

Answer 14

• Mild-moderate hearing loss on right (predominantly)
• mild hearing loss on left at higher frequencies
• not enough info to distinguish whether SNHL or conductive

Question 15

Describe this audiogram

Answer 15

• Bilateral symmetrical hearing loss
• Affecting higher frequencies
• Most likely due to old age (presbycusis)

Question 16

Describe this audiogram

Answer 16

• Mild conductive R sided hearing loss

Question 17

Describe this audiogram

Answer 17

• triangles → bone conduction (unmasked) = normal
• bilateral symmetrical mild hearing loss in both ears
• therefore, a conductive hearing loss
• could be caused by glue ear (otitis media w/ effusion)

The tympanogram is abnormal also, reads ear canal volume. Flat trace would suggest perforated ear drum, but this curve suggests effusion (glue ear).

Question 18

Describe this audiogram

Answer 18

• Looking at right ear
• mainly moderate conductive hearing loss
• mild-moderate hearing loss w/ bone conduction → sensorineural element
• suggests issue in outer/middle as well as inner ear
• MIXED hearing loss!
• could have perforation + ear infection + presbycusis

Question 19

We have mentioned that pure tone audiometry is a subjective hearing test.

What are examples of objective hearing tests?

Answer 19

• otoacoustic emissions (OAE) → test of outer hair cell cochlear function, forms part of newborn hearing screen
• auditory brainstem responses (ABR) → test of auditory nerve function + forms part of newborn hearing screen testing

Question 20

What are examples of hearing tactics?

Answer 20

• get their attention before speaking
• face them
• get to the point
• don’t cover your mouth
• don’t turn away while talking
• don’t shout - distorts mouth + lip patterns
• don’t speak too quickly
• cut down ambient noise
• reduce distance to 1.5m

Question 21

What are the different types of hearing aids?

Answer 21

• Electronic aids → pt needs to have some residual hearing, can sit in ear canal
• Bone achored hearing aids → good for conductive deafness or where out-the-ear-aids are unsuitable (eg. eczema), utilises bone conduction
• Cochlear implants → where auditory nerve is functional, and pt has already developed speech + language skills (or infants), usually only for profoundly SNHL

Question 22

What is the difference between conductive and sensorineural hearing loss?

Answer 22

• Conductive → the conduction of the sound to cochlea is impaired, can be caused by external and middle ear disease
• Sensorineural → due to a defect in the conversion of sound into neural signals or in the transmission of those signals to the cortex, can be caused by disease of the cochlea, acoustic nerve (CN VIII), brainstem or cortex

Question 23

What are the causes of conductive hearing loss?

Answer 23

• wax (cerumen)
• otitis externa
• foreign body
• acute/chronic otitis media
• trauma → tympanic membrane or ossicles
• otosclerosis
• middle ear tumours
• cholesteatoma

Question 24

What are the causes of sensorineural hearing loss?

Answer 24

• presbycusis
• noise-induced traumatic loss
• acoustic neuroma
• Meniere’s
• trauma
• infection → meningitis, measles, mumps
• intra-uterine infection → TORCH
• birth injury
• genetic → Alport’s, Jervell-Lange-Nielson
• autoimmune
• ototoxic drug exposure

Question 25

What is **presbycusis**?

Answer 25

* _common cause of hearing loss_ * affecting more than half of all adults by age 75 * **multiple factors** influence onset: genetic predisposition, low socioeconomic status, noise exposure, smoking, hypertension, diabetes, vascular disease * hallmark is **progressive, symmetric loss of high-frequency hearing loss** over many years * _Rx_ → hearing aids, hearing tactics

Question 26

**Ototoxicity** → what drugs cause permanent and temporary hearing loss?

Answer 26

* **antineoplastics** (cisplatin, carboplatin) → _permanent_ HL * **loop diaretics** → rapid _reversible_ oedema in stria vascularis * **salicylates** → _temp_ threshold shifts during dosing across most frequencies + tinnitus * **aminoglycosides** → _permanent_ progressive loss of hair cells, affects high freq first, progressing to lower freqs, affects vestibular organs, may become dizzy/imbalanced * **antimalarials** → _temporary_ HL + tinnitus * **macrolides** (-mycin) → temporary HL

Question 27

Describe the features of **noise-induced hearing loss**

Answer 27

* can be caused by **one time exposure** to an intense 'impulse' sound * or can be caused by **cont exposure** to loud sounds over period of time * 17K in UK suffer hearing loss + tinnitus caused by XS noise at work * results in damage to hair cells * **temporary threshold shift** (TTS) is when there is brief hearing loss that occurs after noise exposure and completely resolves after a period of rest * after repeated exposures to noises intense enough to produce TTS, eventually a **permanent** threshold shift will occur

Question 28

What **advice** can you give a patient to **prevent** deafness from listening to loud music?

Answer 28

**_MUSIC_** * **MP3** players can be too loud for your ears - turn it down! * **Use** chillout zones in clubs + take reg breaks from loudest areas * **Stand** back from speakers - your ears will thank you * **Invest** in some noise cancelling headphones * **Carry** earplugs with you - they won't block music out, just make it safer

Question 29

What are the features of a **vestibular schwannoma (acoustic neuroma)**?

Answer 29

* benign, usually slow growing tumour from an overproduction of Schwann cells * annual incidence ~1 per 100,000 * presentation → **asymmetrical hearing loss**, tinnitus, dizziness, CN VII symptoms large * Dx → **MRI** of internal acoustic meatus * **Rx** → dependent on size + symptoms - monitoring, radiotherapy + surgery

Question 30

What are the features of **Meniere's Disease**?

Answer 30

* _recurrent_ **vertigo** lasting 20mins to several hours * w/ **unilateral tinnitus**, **aural fullness** + **fluctuating hearing loss** * rare → prevalence ~20-200/100,000 * likely 2^o to endolymphatic hydrops * in _early stages_ → vestibular/cochlear symptoms may occur in isolation, hearing loss (low freq) + tinnitus recede fully * after 1-2 years **complete** set of symptoms usually established * _later stages_ → progressive deterioration of hearing **superimposed** on fluctuations * **Rx** → symptomatic relief, numerous treatments for prophylaxis (betahistine, low-salt diet, bendroflumethiazide)

Question 31

What is **_sudden_ hearing loss**?

Answer 31

* **defined as 30dB hearing loss over 3 consecutive frequencies, in less than 3 days** * annual incidence 5-20/100,000 * 95% unilateral (~90% idiopathic) → 30-65% spontaneous recovery * 5% bilateral (most identified aetiologies) → ~20% complete/partial recovery

Question 32

Sudden conductive causes of hearing loss tend to include **trauma**. What are the causes of **sudden sensorineural** hearing loss?

Answer 32

* **TOXIC** → alcohol, cocaine, heroin, ecstasy, opioid, benzo, antivirals, retinoid, chemo, NSAIDs, immunosuppressives, bisphosphonates, insecticides, gentamicin * **AUTOIMMUNE** → AI inner ear disease, cogan's, kawasaki, guillain-barre, scleroderma, anti-phospholipid syndrome, crohn's, polychondritis * **INFECTIOUS** → mumps, HIV, HSV, cryptococcal meningitis, bacterial meningitis, viral URTI * **IATROGENIC** → micro-emboli surg complications, GA haemodynamic complication, GA ototoxicity * **VASCULAR** → CV accident, migraine-associated vasospasm, sickle cell * **NEOPLASTIC** → CPA or petrous meningioma, neuolymphatosis, leptomeningeal carcinoma, vestibular schwannoma, acoustic neurofibroma, meningeal carcinoma

Question 33

Bilateral sudden sensorineural hearing loss is a **medical emergency**. What are the immediate **investigations** + **management**?

Answer 33

* **investigations** → * audiometric testing * MRI internal auditory meatus / CT petrous bones * blood tests * **management** → * treat underlying cause (if found) * steroids

Question 34

What is **pre-lingual deafness** and its impact?

Answer 34

* hearing loss that occurs **before** development of speech + language * severity will determine outcome * those who cannot hear \<90dB will acquire **comprehension difficulties** * children who become deaf after the development of some language (even if v basic) will demonstrate a much higher level of **linguistic achievement** than those who have had no language exposure * **congenital** causes → genetic, prenatal infections, prematurity * **acquired** causes → infections (meningitis, mumps), trauma * 90% of pre-lingually deaf children are unlikely to ever develop good speech + speech reception (even w/ hearing aids and early speech intervention) * reading skills are impaired * **delayed social development** + **social isolation** (less of a problem if child identified w/ 'deaf culture')

Question 35

What is **post-lingual deafness** and its impact?

Answer 35

* also causes communication difficulties, but bc speech is already established, communication can be **augmented** by measures discussed previously * can cause social isolation, anger, depression + denial * as well as interventions to augment hearing, **supportive** measures are also required