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Introduction

Deafness is a partial or total inability to hear. WHO defines deafness as hearing threshold of 20dB or better in both ears.

Classification

[Deafness] may be classified according to WHO into 5 subtypes/groups:

• Mild- Hearing losses between 26 and 40 dB
• Moderate- Hearing losses between 41 and 55 dB
• Moderately severe- Hearing losses between 56 and 70 dB
• Severe - Hearing losses between 71 and 90 dB
• Profound - Hearing losses greater than 91 dB

Pathophysiology

In general, sound waves reaching outer ear are conducted down the ear canal to vibrate eardrum, which in turn, transmitted to inner ear via 3 tiny bones. The fluid in the inner ear moves the hair cells which generate impulses that is conducted to brain via cochlear nerve. Any alteration or obstruction in these pathways can lead to hearing loss. Often, hearing loss is caused by long-term exposure to loud noises, that damage the hair cells.

Causes

Common causes of hearing loss include: Based on location

• External Ear
  • Congenital atresia of external auditory meatus (EAC)
  • Infection- Otitis externa
  • Trauma
  • Tumour
  • Benign Polyp
  • Cerumen
• Middle Ear
  • Atresia or malformation of ossicular chain
  • Eustachian tube dysfunction
  • Infection- Otitis media
  • Cholesteatoma
  • Otosclerosis
  • Jugulotympanic paragangliomas (glomus tumors)
  • Middle ear barotrauma-sudden, large change in ambient pressure, often during diving or flying
• Inner Ear
  • Congenital malformation of cochlea
  • Presbycusis- old age related hearing loss
  • Infection- Viral cochleitis
  • Meniere disease
  • Noise exposure
  • Inner ear barotrauma
  • Ototoxic drugs
  • Systemic diseases- diabetic vasculopathy can cause cochlear ischemia
  • Tumors- acoustic neuroma

Differential Diagnosis

Conductive hearing loss	Sensory hearing loss	Neural hearing loss	Central hearing loss
Acute causes cerumen impaction Tympanic effusion Eardrum perforation (traumatic) Acute infection of ear Chronic causes Cholesteatoma Otosclerosis tympanosclerosis Defect in eardrum or ossicular chain disruption due to chronic infection Malformation	Acute causes Loud noise induced(blast trauma, explosion trauma) Bacterial/Viral Labyrinthitis Idiopathic sudden sensorineural hearing loss Permanent causes Occupational noise exposure Ototoxic drugs Hereditary inner ear malformation Presbycusis	Acoustic neuroma Tumors of cerebellopontine angle(meningioma,chordoma) Compression syndrome	Hemorrhage Infarctions Intracranial tumor Multiple sclerosis

Epidemiology and Demographics

The incidence of hearing loss increases with age. In the Beaver Dam cohort in the United States, the prevalence of hearing loss, defined by audiometry:

●3 percent ages 21 to 34

●6 percent ages 35 to 44

●11 percent ages 44 to 54

●25 percent ages 55 to 64

●43 percent ages 65 to 84

World Health Organization estimates that hearing loss affects 538 million people worldwide.

Risk Factors

The most potent risk factor in the development of hearing loss is aging. Other risk factors include hereditary causes, occupational noises such as noises from factories, recreational noises such loud noises from firearm or jet engine, ototoxic drugs and illness such as meningitis or diabetes. Some other risk factors for hearing loss could be due to head trauma and viral infections.

Diagnosis

The diagnosis of hearing loss is based on the inability to hear sound( louder than 20dB) based on audiometer test.

Treatment

Patients with infective aetiology for hearing loss are treated with Antibiotics and analgesics, whereas patients with non-infective/ structural causes are managed with hearing aids and cochlear implants .