Types of hearing lossCommon causes of hearing lossEvaluation of hearing lossManagement

TerminologyNormal Hearing: PTAs < 25 dB

Hearing Impairment: PTAs 25-92 dB

Deaf: PTAs > 92 dB

Conductive – Disorders involving the conduction of sound to the cochlea.

Sensori-neural – Disorders involving the cochlea (usually the hair cells) or 8th N.

Mixed

Two related terms:

Peripheral – Not central; i.e., conductive or sensorineural.

Retrocochlear – Disorders involving anatomical structures beyond the cochlea; i.e., 8th N, brain stem, auditory cortex.

Conductive Hearing Disorders

1. External Ear

Congenital malformations. There are many of these. Most serious is congenital atresia – collapse or closure of the EAM (ear canal). May occur in isolation, but typically associated congenital malformations of the middle ear as well.

Impacted wax (cerumen) – results in mild hearing loss; easily treated by removal of the wax.

2. Middle Ear

a. Otitis Media

By far the most common cause of conductive hearing loss.

By far the most common health problem in children.

Otitis media means inflammation of the middle ear.

Suppurative or Purulent Otitis Media: As the disease progresses, the fluid can become infected and thickens into pus.

Some Additional Terminology

Acute vs. Chronic OM: A specific bout of OM with pain, accumulation of fluid, etc., is called acute otitis media. If OM lasts more than 2-3 months, the condition is known as chronic otitis media.

Recurrent OM: Frequent bouts of OM: OM is treated successfully, then returns, then treated, then returns … This gets old after a while but is pretty common.

Treatment of Otitis MediaMost common treatment by far: Antibiotics (especially amoxicillin)

Common treatment for recurrent or chronic OM: PE Tubes (PE = pressure equalization). This is a small plastic tube inserted into the TM. Why would such a tube be expected to treat OM?

b. Otosclerosis (note: topic here is still conductive HL, sorted by cause)

Begins as a soft, spongy growth of new bone – may appear anywhere in the ME, but most often near oval window.

Later hardens (i.e., becomes sclerotic)

Progressive. Beginning in childhood. For that unlucky 10%, HL typically begins in late teens, early 20s.

Maximum HL seldom worse than ~50-60 dB.

Treatment: Stapedectomy (removal of stapes and replacement with an artificial stapes)

prosthetic stapesincus

Stapedectomy

c. Cholesteatoma invades the ME; usually grows rapidlyCan: (1) destroy the ossicular chain, (2) invade the cochlea, or (3) break through the thin shelf of bone that forms the superior surface of the ME cavity, invading the meninges.

Sensorineural Hearing Loss

General: By far the most common underlying cause of SN HL is damage to the hair cell transducers. In these most common cases, the auditory nerve and central auditory pathway are intact, but stimulation of the auditory nerve is abnormal due to damaged hair cells. There are many possible reasons for hair cell damage.

a.Presbycusis

• Hearing loss associated with aging

• Most common cause of SN HL – and most common cause of HL overall

• Presbycusis begins in adolescence.

b. Noise-Induced Hearing Loss

Exposure to high levels of noise can damage HCs and cause SN HL. Two types:

Acoustic trauma:

Injury due to brief exposure to very intense sounds such as gun shots, artillery fire, explosions, etc.

HL may be severe and permanent, but substantial recovery is common.

Long-term noise exposure (more common):

Damage results from long-term exposure to high levels of noise.

Common in some occupational settings – heavy manufacturing and agriculture being the most common.

Amount of inner-ear damage depends on the combination of:

Intensity of the noiseLength of exposure

Audiometric Pattern is distinctive (audiogram on right shows more advanced progression than left)

Note:

(1) Dip or “notch” at ~3-6 kHz

(2) High frequencies more affected than lows

c. Ototoxic DrugsCertain drugs can cause SN HL. Toxicity effects vary from mild and temporary to severe and permanent.

Some very common drugs such as aspirin

An especially important group of antibiotics are notoriously ototoxic. Examples include neomycin, streptomycin, kanamycin.

Other drugs????

d. Meniere’s Disease

Serious, often debilitating disease of hearing and balance of uncertain cause.

MD affects a single ear in about 75% of cases.

Four major symptoms:

(1)Periodic episodes of rotary vertigo (the sensation of spinning) or dizziness (the “Meniere’s attack”)

(2)Fluctuating, progressive, low-frequency hearing loss

(3) Roaring or ringing tinnitus

(4) A sensation of "fullness" or pressure in the ear

e. Infections

Bacterial or viral infections that invade the inner ear can cause SN HL and disruptions of vestibular function.

Generic term for infections that invade the inner ear: labyrinthitis. Meningitis can sometimes spread to the inner ear and result in labyrinthitis.

Other infectious diseases: Mumps, measles, meningitis, encephalitis, chicken pox, influenza, and syphilis can also invade the inner ear and cause SN HL and/or vestibular symptoms.

f. 8th N Tumors (acoustic neuroma)

• Benign (i.e., nonmalignant) tumor that exerts pressure on 8th

• Most common symptom: hearing loss (mild initially), often accompanied by tinnitus

• Vestibular problems may also occur

• Early diagnosis is tough – early-stage symptoms are un-dramatic

g. Congenital Causes

Congenital: Present at (or before) birth

This is to be distinguished from acquired or adventitious hearing loss.

Congenital etiologies may be hereditary or non-hereditary.

(1) Non-Hereditary Causes

(a) Maternal rubella (German measles)

especially in the 1st trimester. Effects can include:

Heart defects, brain damage, various visual impairments

SN HL, often profound

(b) Anoxia (asphyxia)

Insufficient oxygen during birth/delivery can cause all sorts of problems for the newborn.

(c) any other etiologies that are less common

(2) Hereditary Causes

Genetic factors are thought to cause more than 50% of all incidents of congenital hearing loss in children

(a)autosomal dominant

(b) autosomal recessive

Approximately 80% of inherited hearing loss is autosomal recessive.

Syndromes:

Inherited hearing loss can also be associated with a complex of inter-related symptoms in the form of a syndrome.

Waardenburg Syndrome

Alports

Brachi-Oto-Renal syndrome

Waardenburg Syndrome

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History◦ Prenatal: infection, medication◦ Perinatal: risk factors◦ Postnatal: infection, speech and language milestones◦ Family:

hearing loss in first and second degree relatives Hearing loss occurred before age 30 Consanguinity or common origin from ethnically isolated areas

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Physical exam: features of syndromic hearing loss◦ Hair color: white forelock, premature graying◦ Facial shape◦ Skull shape◦ Eye: color, position, intercanthal distance, cataracts, retinal findings◦ Ear: preauricular pit, skin tags, shape and size of pinna, abnormality of

EAC and TM◦ Oral cavity: cleft◦ Neck: brachial anomalies, thyroid enlargement◦ Skin: hyper/ hypopigmentation, café-au-lait spots◦ Digits: number, size, shape◦ Neurological exam: gait, balance

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Audiologic evaluation Lab testing: based on history and physical exam

◦ Torch titers◦ CBC and electrolytes◦ Urinalysis◦ thyroid function test

Radiological study:◦ CT temporal bone is the test of choice

Dilated vestibular aqueduct Semicircular canal absence or dysplasia Internal auditory canal narrowing or dilation

◦ Renal ultrasound

PTA IMPEDANCE

PTA SPEECH AUDIOMETRY STAPEDIAL REFLEX, ABLB BERA MRI

PARTS OF HEARING AID:

MICROPHONE: converts acoustic mechanical energy into weak electrical energy.

AMPLIFIER: converts this weak electrical energy into strong one by increasing the voltage.

The strong electrical energy is converted into mechanical energy by the RECEIVER.

Developed by HLA-Wake County, Raleigh, NC

Basic Styles◦ BTE◦ ITE◦ ITC◦ CIC

Middle Ear Implantable Bone Conduction/BAHA

Technical Solutions

An electronic device that can provide useful hearing and improved communication abilities for persons who have severe to profound sensorineural hearing loss.

Developed by HLA-Wake County, Raleigh, NC

Transmission◦ Hard Wired◦ Magnetic (loop)◦ FM◦ IR

User Interface◦ Headphones◦ NeckLoop and Silhouette◦ Direct Audio Input (DAI)

Technical Solutions

Hear Better:Meetings/Classroom

In the car

Noisy Restaurants

Telephone

TV/Stereo

Movies

Computer

Solves• Distance• Noise

Developed by HLA-Wake County, Raleigh, NC

Flashers for Doorbell and Phone Baby Criers Vibrating Alerters and Bed Shakers Alarm Clocks (Loud, Vibrating, Light Flashing) Fire Alarms with Strobe Lights Captions

◦ Closed◦ Open◦ Subtitles

Technical Solutions

Hearing loss is common Conductive hearing loss is mostly surgically

correctable Sensorineural hearing loss needs hearing aids Many types of SNHL can be prevented Early identification is the key to successful

management Assessment is by a battery of tests Should refer kids early if hearing loss is

suspected