1. CAUSES OF HEARING IMPAIRMENT
TOPIC 2
CAUSES OF HEARING
IMPAIRMENT

2. Outer and Middle Ear Disorders
Structural defects due to embryologic malformations
Structural changes secondary to infection or trauma
OUTER AND MIDDLE EAR DISORDERS
These pathologies are commonly of two types
- structural defects due to embryologic malformations
- structural changes secondary to infection or trauma

3. Outer Ear Disorders Microtia and atresia
• microtia and atresia--these are the most common congenital malformations of the auricle (pinna) and the external canal.

4. “an abnormal smallness of the auricle”
Microtia
“an abnormal smallness of the auricle”

5. Atresia
“the absence of an opening of the external canal”

6. Outer Ear Disorders Microtia and atresia Impacted cerumen
Perforation of the tympanic membrane
• Impacted Cerumen--very common cause of temporary conductive HL. Very treatable and preventable. HL that results is flat, conductive, and of varying degree.

7. Perforation of the TM
• Perforation of the tympanic membrane--These usually occur either by trauma or secondary to OM.
An example of the audiogram illustrating the flat, mild, conductive hearing loss that can occur with a perforated tympanic membrane

8. Outer Ear Disorders Microtia and atresia Impacted cerumen
Perforation of the tympanic membrane
Other
• Other disorders of the outer ear---there are others, but not common and usually don’t affect hearing unless the auditory meatus is blocked

9. Middle Ear Disorders Otitis Media
Most common cause of transient conductive hearing loss in children
Inflamation of the middle ear
Caused by eustachian tube failure
• Otitis Media--the most common cause of transient conductive HL in kids. OM is an inflammation of the middle ear. Caused by eustachian tube malfunction. When it is accompanied by middle ear effusion (fluid) it often causes a conductive HL.

10. Otitis Media
Three examples of the usual characteristics of a conductive hearing loss arising from otitis media
Ways to classify OM:
- OM w/out effusion
- fluid types:
- duration:

11. Ways to Classify Otitis Media
With or without effusion
Fluid type
Serous
Suppurative
Mucoid

12. Ways to Classify Otitis Media
With or without effusion
Fluid type
Duration
Acute
Chronic
Subacute
Persistent
Recurrent

13. Otitis Media Facts
76-95% of all kids will have one episode of OM by age 6
Prevalence is highest during the first two years of life
50% of all kids with one episode before their first birthday will have 6 or more bouts within two years
Most episodes occur in winter and spring
Risk factors
Cleft palate
Down syndrome
Native Americans
Urban poor
Day care
Secondhand smoke
76-95% of all kids will have one episode of OM by age 6. Prevalence is highest during the first 2 years, then declines after that. 50% of all kids with one episode before their first birthday will have 6 or more bouts within 2 years. Most episodes occur in winter and spring.
Some populations are more prone to OM--kids with cleft palate or other craniofacial anomalies, Down syndrome, Native Americans, urban poor, day care kids, kids exposed to secondhand smoke.

14. Middle Ear Disorders
Otitis media
Otosclerosis

15. Otosclerosis
“a bone disorder that affects the stapes and the bony labyrinth of the inner ear. The disease process is characterized by resorption of bone and new spongy formation around the stapes and oval window”
• Otosclerosis--a bone disorder that affects the stapes and the bony labyrinth of the inner ear. The disease process is characterized by resorption of bone and new spongy formation around the stapes and oval window.

16. Otosclerosis Facts: Hereditary
Women are more likely to develop the disorder
Usually bilateral
progressive

17. Middle Ear Disorders
Otitis media
Otosclerosis
Cholesteatoma

18. Cholesteatoma
“an epithelial pocket that forms on the tympanic membrane. Once the pocket forms, the normal shedding of epithelium results in growth of the tumor”
• Cholesteatoma--usually a secondary condition to OM. A cholesteatoma is an epithelial pocket that forms on the tympanic membrane. Once the pocket forms, the normal shedding of epithelium results in growth of the cholesteatoma, or tumor, which is capable of reabsorbing adjacent bone

19. Middle Ear Disorders Otitis media Otosclerosis Cholesteatoma Other
Physical trauma
• Other middle ear disorders
- physical trauma
- barotrauma
- Middle ear tumors

20. Physical Trauma of the Middle Ear
Here’s an example of an audiogram resulting from disarticulation of the ossicular chain

21. Middle Ear Disorders Otitis media Otosclerosis Cholesteatoma Other
Physical trauma
Barotrauma
Middle ear tumors
Glomus tumor

22. Cochlear Disorders Syndromes and inherited disorders
Syndromic disorders
Nonsyndromal disorders
• Syndromes and inherited Disorders
- syndromic disorders: occurring as part of a constellation of other medical and physical disorders that occur together.
- nonsyndromic disorders: autosomal recessive or dominant genetic conditions in which there is no other significant feature besides HL

23. Syndromes and Inherited Disorders Resulting in Sensorineural Hearing Loss

24. Types of Nonsyndromic Disorders
Dominant
Dominant progressive
Dominant progressive with adult onset
Recessive hereditary SNHL
X-linked

25. Cochlear Disorders Syndromes and inherited disorders
Noise induced hearing loss
• Noise induced HL---very common cause of SNHL in adults. Right up there with presbycusis. This can happen with a one-time exposure to a very loud sound or long-time exposure to constant, softer sounds.

26. Noise Induced Hearing Loss
The degree of SNHL depends on
The intensity of the noise
The spectral composition of the noise
The duration of exposure
Individual susceptibility
Effects of noise are cumulative. How damaging sounds are to the cochlear are dependent on
- the intensity of the sound.
- the spectral composition of the sound
- duration of exposure
- individual susceptibility

27. OSHA Damage Risk Criteria

28. Noise Induced SNHL
Noise notch
Cummulative
Progressive

29. Cochlear Disorders Syndromes and inherited disorders
Noise induced hearing loss
Other trauma
Infections
• Other trauma--physical trauma that causes a fracture of the temporal bone and leakage of endolymph.

30. Infections Congenital Cytomegalovirus HIV Rubella Syphilis
Toxoplasmosis
• Infections--we discussed congenital infections most commonly associated with SNHL that included:
- cytomegalovirus
- HIV
- rubella
- syphilis
- toxoplasmosis

31. Infections Acquired Herpes Zooster Oticus (Chicken Pox) Mumps Syphilis
Acquired infections: can be caused by viral or bacterial infections--and by fungi
Some common acquired viral infections that can cause HL
- Herpes Zoster Oticus--caused by a virus that also causes chicken pox.
- Mumps----HL is rare but can occur related to encephalitis.
- syphilis--occurs in the secondary or tertiary stage of the disease.

32. Cochlear Disorders Syndromes and inherited disorders
Noise induced hearing loss
Other trauma
Infections
Ototoxicity
• Ototoxicity--certain drugs and chemicals are toxic to the cochlea

33. Ototoxicity Some antibiotics that are often ototoxic: Amikacin
Dihydrostreptomycin
Garamycin
Gentamicin
Kanamycin
Neomycin
Netilmicin
Streptomycin
Tobramycin
Viomycin

34. Ototoxicity Chemotherapy Carboplatin Cisplatin
Drugs that cause reversible hearing loss
Quinine
Salicylates (aspirin)
Loop diuretics
Drugs that may be harmful during pregnancy
Accutane
Dilantin
Thalidomide

35. Cochlear Disorders Syndromes and inherited disorders
Noise induced hearing loss
Other trauma
Infections
Ototoxicity
Meniere’s Disease
• Meniere’s Disease--endolymphatic hydrops. Triad of symptoms includes tinnitus, vertigo, and SNHL.

36. Meniere’s Disease Symptoms Tinnitus Vertigo
Unilateral sensorineural hearing loss

37. Cochlear Disorders Syndromes and inherited disorders
Noise induced hearing loss
Other trauma
Infections
Ototoxicity
Meniere’s Disease
Presbycusis
• Presbycusis--decline in thresholds due to aging. The leading contributor to HL in adults. Estimates are that 25-40% of those over 65 have this.

38. Presbycusis

39. Central Auditory Disorders
VIII Nerve tumors
Other diseases of the VIII Nerve
Neural disorders
Cochlear neuritis
Diabetes mellitus
Brain Stem disorders
Infarcts
Gliomas
Multiple sclerosis
Temporal Lobe disorders
CNS DISORDERS
The nature of the HL that accompanies CANS disorders vary as a function of location of the lesion--more peripheral, more apparent. Disruption in speech perception also gets more subtle as the lesion becomes more central.
• VIII N. Tumors
• Other tumors, cysts, and aneurysms can affect the VIII nerve and the cerebellopontine angle.
• Neural disorders:
- cochlear neuritis--
- diabetes mellitus
• Brain Stem Disorders--these include infarcts, gliomas (fast growing tumors), and multiple sclerosis.
• Temporal-Lobe Disorder