hearing loss

HEARING LOSS

Zagada, Timothy M.

HEARING LOSS

HEARING AND HEARING LOSS

• Hearing- transduction of sound to neural impulses and its interpretation by the CNS

• Hearing loss- defect at any level from sound transduction to interpretation

TYPES OF HEARING LOSS

• Conductive- sound is not conducted efficiently through the outer ear canal to the eardrum and the tiny bones (ossicles) of the middle ear

• Sensorineural (SNHL)- damage to the inner ear (cochlea), or to the nerve pathways from the inner ear to the brain.

• Mixed• Central- Problem lies in the central nervous

system

KNOWN CAUSES

HEREDITARY SENSORINEURAL HEARING LOSS

• Hereditary- 1/3 of all cases of SNHL• Syndromic- Usually present at birth usually AR

• Ex; Treacher-Collins syndrome

• Non-syndromic- based on onset• Congenital form• Late onset form- more common, tend to

be AD, manifested after birth

NOISE INDUCED HEARNG LOSS

Can cause direct mechanical trauma to cochlea

• Acute acoustic trauma- sudden intense sound event of short duration

• Exceeds 140 db and pressure rise is very short (<1.5ms)• Ex; gunshot

• Blast injury- pressure wave from an explosive blast• Exceeds 140db but duration of pressure rise is longer (>2ms) • longer frequency spectrum• Ruptured tympanic membrane

NOISE INDUCED HEARNG LOSS

• Acute noise-induced hearing loss- high levels of continuous or intermittent noise for seconds to hours

• Often reversible or partially reversible• muffled sensation and tinnitus• Ex; loud power tools, rock concerts, engine noise

• Chronic noise-induced hearing loss- irreversible cochlear hearing loss

• Typical features of sensorneural hearing loss• Tinnitus can be constant• Safe if levels below 85db for 8hrs/day

TRAUMATIC INJURY TO INNER EAR

• Functional- labyrinthine concussion

• Structural- labyrinthine contusion• Temporal bone fracture• Impact to the skull- accelerating and decelerating

forces• Barotrauma

• Symptoms: nonspecific vertiginous complaints and hearing impairment

LABYRINTHITIS

Infection or inflammatory process affecting the labyrinth or its surrounding

3 routes: Tympanogenic, meningeal and hematogenous

• Tympanogenic- infection/inflammation maybe transmitted through oval or round window

• Acute toxic (serous labyrinthitis)- labyrinth itself is not infected; becomes inflamed by substances released in middle ear.

• Acute supporative- bacterial infection of middle ear spreads to labyrinth.

• Chronic Labyrinthitis- manifested as inner ear damage. • Chronic otitis media as possible cause

LABYRINTHITIS

• Meningeal- Labyrinth maybe infected bilaterally (often strep pneumonia) from intracranial space

• Hematogenous- by viruses and bacteria. Results in hearing loss and disequilibrium

• Typical causative organisms: mumps, meascles, HIV, CMV, spirochetes

Symptoms: Cochlear hearing loss, tinnitus, vestibular symptoms (vertigo, disequilibrium, nystagmus)Vestibular symptoms in patient with otitis media is a warning sign of labyrinthitis

OTOTOXICITY

• Toxic damage to inner ear affects both cochlear and vestibular functions

• Endogenous or exogenous

• Effects generally symmetrical

• Symptom: Tinnitus maybe initial presenting symptom

UNKNOWN CAUSES

PRESBYACUSIS

• Age related (over 50 yr old), symmetrical SNHL• Ageing process• Endogenous genetic predisposition• Cummulative exposure to exogenous factors

• Symptoms: Speech recognition more affected than pure tone

• Diagnosis: Pure tone audiometry- symmetrical SNHL (High tone loss)

SUDDEN SENSORINEURAL HEARING LOSS

• Immediate, unilateral hearing loss with no apparent external cause.

• Symptomatic or Idiopathic• Idiopathic- cause: Viral, vascular, autoimmune

• Symptoms: within seconds to hours. Mild loss of hearing to sudden deafness

• Vestibular symptoms less common

CHRONIC, PROGRESSIVE, IDIOPATHIC SENSORINEURAL HEARING LOSS

• Bilateral SNHL

• Onset before age 50

• Etiology unknown

• Symptoms: Variable- sudden hearing loss or progress gradually

• Frequently associated by tinnitus

• Vestibular symptoms generally absent

• Tuning Fork test

• Pure tone audiometry

• Speech audiometry

• Tympanometry

TEST FOR AUDITORY FUNCTION

TUNING FORK TEST• Differentiate between conductive and SNHL

• Weber and Rinne test

• Weber- TF placed in midline of skull. Vibrations are transmitted by bone conduction

• Normal- Vibrations perceived equally on L+R• SNHL- Lateralizes to better ear• CHL-Lateralizes to affected ear

• Rinne- compares level of air and bone conduction in the same ear.• AC test- TF just outside the ear canal• BC test- TF firmly against mastoid• Normal: AC>BC• CHL: BC>AC• SNHL: AC>BC but both equally depreciated

PURE TONE AUDIOMETRY

• used to identify hearing threshold levels of an individual, enabling determination of the degree, type and configuration of a hearing loss.

• NORMAL HEARING

- both air and bone conduction will be superimposed at each test frequency between 0 to 10 dB.

• CONDUCTIVE HEARING LOSS

- air conduction is < normal bone conduction.

• SENSORINEURAL HEARING LOSS

- both air and bone conduction below

normal threshold at any frequency tested

• Mixed hearing loss

TYMPANOMETRY

• an examination used to test the condition of the middle ear and mobility of the eardrum (tympanic membrane) and the conduction bones by creating variations of air pressure in the ear canal.

• Permits a distinction between sensorineural and conductive hearing loss, when evaluation is not apparent via Weber and Rinne testing.

• Can be helpful in making the diagnosis of otitis media by demonstrating the presence of a middle ear effusion.

• A- Normal• AD- abnormally compliant• AS- Stiff (otosclerosis)

• B- Presence of non-compressible fluid within middle ear space(Otitis Media)

• C-Eustachian tube dysfunction