Sensori-neural Hearing Loss (SNHL)Size of the problem WHO (2005)

• 278 million with disabling hearing impairment• Disabling-moderate (41 d B +) or worse• 364 million- mild hearing impairment• 80 percent in low or middle income countries• Among 20 leading global burden of the disease

Recent Increase is due to• Improved diagnosis and early detection• Longer survival of elderly• Increase in NIHL• Increase in ototoxicity

Sensori-neural Hearing Loss

Importance—profound effect On individuals

• Hinder speech, language and cognitive skill development in pre-lingual children

• Slow progress in schools• Difficulty in obtaining, keeping and performing in any 

occupation• Significant social isolation and stigmatization- poor 

interpersonal developmentSocial and economic

• Substantial cost of treatment and rehabilitation • Loss of productivity

Causes of SNHL

A. CongenitalGenetic

SyndromicNon-Syndromic

Non-genetic (Embryopathies)B. Acquired

Causes of SNHL

Congenital-Genetic (Hereditary) SNHL-SyndromicWaardenburg’s-White  forelock, heterochromia of irisUsher- with retinitis pigmentosaAlport’s- with nephritisPendred- with hypothyroidismMarfan- skeletal defectsJervill –Lange- with abnormal EEG

Causes of SNHL

Congenital-Genetic (Hereditary) SNHL-Non-Syndromic

More common than syndromic1. Autosomal dominant SNHL2. X-linked SNHL3. Autosomal recessive SNHL-more 

common

Causes of SNHL

• Congenital-Nongenetic (Embryopathies)• Aplasia-Michel,Mondini,Scheibe,Alexander• Viral- mumps, measles,• Spirochaetal• Ototoxocity• Trauma

Causes of SNHL

AcquiredIdiopathic SSNHL Perinatal asphyxia and kernicterusLabyrinthitis PresbyacusisOtotoxicity Suppurative otitis mediaCochlear otosclerosis Endolymphatic hydropsTrauma to inner ear Acoustic neuromaNIHL NOHL

Causes of SNHL

Acquired• Vascular lesions of inner ear• Metabolic-renal failure, diabetes• Systemic viral infections- mumps, measles,• Systemic bacterial infections- meningitis encephalitis, enteric fever

• Perilymph fistula

Ototoxicity

Definition:Tendency of certain therapeutic agents to cause functional impairment of inner ear as a side effect of pharmacotherapy

Route of administration:Topical- creams, ointments, drops, sprays, inhalation, irrigationSystemic- IM/ IV

Drugs/Chemicals1. Aminoglycosides   high risk  permanent2. Cytotoxic agents-Cisplatin  high risk permanent3. Industrial chemicals-Toluene, benzene  high risk Permanent4. Polypeptide antibiotics- Vancomycin low risk permanent5.Macrolides low risk  temporary6. Loop diuretics-  low risk temporary7. Salicylates low risk temporary8. Quinine derivatives unknown Temporary9. Others-– Anticonvulsants c. Barbiturates, – Beta-blockers,  d. Muscle relaxants 

Aminoglycosides

• Streptomycin, dihydro-streptomycin, kanamycin, neomycin, gentamicin, tobramycin, sisomycin, amikacin, dibekacin,  netilmycin,  paromycin, ispamicin

• Mechanism-effect on sensory neuro-epithelium of the inner ear especially outer hair cells of the organ of Corti and type I hair cells of Crista ampulli

Aminoglycosides

• Widely used because potent and cheap• Still used in drug resistance tuberculosis, neonatal sepsis

• In 1-5% of patients exposed• Factors influencing-dose, duration, liver and kidney disease,  bacteremia, concomitant use of other agents, genetic predisposition

• Some are cochleotoxic, some vestibulotoxic

Cytotoxic Agents

Cisplatin, carboplatin • Effective in solid head and neck squamous cell carcinoma• Highly ototoxic in about 50 % of patients but the exposed population is low• Loss of mainly outer hair cells

Loop Diuretics

Frusemide , ethacrynic acid, bumetanide•Moderate to low percent of population at risk•Mechanism

Reversible reductions of endocochlear potential

Electrolyte changes in inner ear fluidsHistologic changes in stria vascularis

Industrial Chemicals

• Toluene-used in printing and wood finishing,• Benzene- used in plastic industry

Permanent hearing loss in animals but inconclusive evidence in man

Polypeptide Antibiotics

Vancomycin, Viomycin• Not aminoglycosides• Less commonly used and less toxic • Ototoxic when given at higher doses for longer period of time

Macrolides

Erythromycin, azithromycin, clarithromycin• Transient ototoxicity when used  in high doses• Reduction in transient evoked otoacoustic emissions

Salicylates

• Used for their anti-inflammatory, antipyretic, analgesic and antiplatelet effects

• In low doses protect inner ear from gentamicin induced ototoxicity but ototoxic in higher doses

Quinine Derivatives

• Widely used as antimalarial • Exposed population at risk very high

Ototoxicity

Clinical features• Tinnitus often the first symptom• SNHL-high tone more than low ones• Vertigo and disequilibrium• Oscillopsia- with aminoglycosides

Inability to focus sharply and jumping of the distant objects

Ototoxicity

Prevention and Treatment1. Avoidance of ototoxic agents as far as practicable2. Careful monitoring and early recognition3. Cessation of treatment and substitution by a different 

agent4. SNHL-hearing aid5. Tinnitus-if disturbing-mild hypnotic and tinnitus masker6. Vertigo and disequilibrium –reassurance with 

physiotherapy and head exercises

Presbyacusis

• New terminology--- age related sensori-neural hearing impairment

• Result of aging process and inevitable• Sixth decade onwards, if genetic predisposition and NIHL 

earlier also• Predisposition--Environmental factors 

Noise exposure,  smoking, Alcoholism, high systolic blood pressure Blood hyper viscosity 

Presbyacusis

Histopathological changes in the inner ear• Sensory-Hair cell degeneration and loss• Neural-degeneration of neurons and ganglions• Metabolic-Degeneration of stria vascularis• Mechanical-degeneration of supporting cells, membranes

Presbyacusis

Clinical features• Hearing impairment – slow and insidious, lack of clarity than loss of volume• “Don’t shout, I’m not deaf”• Tinnitus often the presenting symptom and sometimes may be troublesome

Presbyacusis

Management• Speaking in a clear and articulated voice close to the patients ear• Hearing aid- but in some amplification may not help

Noise induced hearing Loss (NIHL)

Reduction in auditory acuity associated with noise exposure --social, recreational, occupational 

Types• Temporary threshold shift (TTS)- Lasting hours to days, reversible

• Permanent threshold shift (PTS) - Irreversible• Acoustic trauma- When a single exposure to intense trauma leads to immediate hearing loss

Noise induced hearing Loss (NIHL)

Pathology- various hypothesisMetabolic changes- TTS

Excessive glutamase release,  cochlear hypoxia

Structural changes –PTSDepolymerization of actin filaments in sterociliaSwelling of stria vascularis, nerve endings, supporting cells- necrosis

Noise induced hearing Loss (NIHL)

Predisposing factor- Variable individual susceptibility

Genetic predispositionSmokingDiabetesOtotoxicityCardiovascular diseases

Noise induced hearing Loss (NIHL)

Diagnosis—clinical• Tinnitus is the usual initial symptom with or without hearing impairment• PTA-High tone hearing loss with a notch centered on 4 kHz

Noise induced hearing Loss (NIHL)

Treatment• “Prevention is better than cure”• Awareness/Legal provisions• Reduction of noise level at place of work• Use of hearing protection devicesIntensity->85 dB, Duration- >8 hours per day 5 days a week

Idiopathic Sudden Sensori-neural Hearing Loss

Definition:30 dB or more sensori-neural hearing loss at least in 3 consecutive frequencies occurring in less than 3 days• Medical emergency• Diagnosis by exclusion  of other causes on the basis of history, clinical examination,, investigations and MRI

Causes- Postulated• Viral, vascular, haematological, membrane rupture, autoimmune etc.

Idiopathic Sudden Sensori-neural Hearing Loss

Treatment- many agents, no single agent universally popular

Steroids Antivirals Carbogen  VasodilatorsVitamins  Antioxidants

• TUTH-Hydrocotisone IV in high doses gradually tapered over two weeks

Idiopathic Sudden Sensori-neural Hearing Loss

Prognosis- Spontaneous remission common in about 75%• Complete recovery-hearing within < 10 dB • Partial recovery-hearing within 50 % or more of prehearing• No recovery-less than 50 percent recovery 

Non -Organic Hearing Loss (NOHL)

• Hysterical or malingnering- recruits or prisoners

• Disproportionate and inconsistent hearing test results

• Stenger tuning fork test• Confirmed by stapedial reflex and evoked response audiometry

Trauma to Inner Ear

• Fracture of temporal boneTransverse-U/L Severe sudden SNHL

• Labyrinthine concussionHead injury –chemical labyrinthitis

• IatrogenicSurgical damage to Oval Window, Labyrinth