Description

• Decrease in the ability to comprehend sound. It can be partial, complete, unilateral or bilateral.
• Types of hearing loss include conductive hearing loss (CHL or air–bone gap), sensorineural hearing loss (SNHL), or mixed hearing loss.
• System(s) affected: Auditory; External and middle ear (CHL), or inner ear (SNHL)

Epidemiology

• All ages affected; common in children (CHL) and elderly (SNHL)
• Predominant sex: Male = Female

• 3/10 people >60 years of age
• At least 1.4 million children (≤18 years)

• ~50% of people age >85 years have hearing loss.
• Hearing aids are underutilized.
• Loss of communication is a source of emotional stress and a physical risk for elderly.

• 1–3/1,000 infants have hearing loss.
• Mandatory newborn screening (OAE and ABR testing are ideal)
• Audiologic testing after major intracranial infection (meningitis)

Pregnancy Considerations
Otosclerosis (a CHL) can worsen during pregnancy.

Risk Factors

• Conductive:
  • Chronic sinusitis; allergy
  • Cigarette smoking
  • Sleep apnea with continuous positive airway pressure (CPAP) use
  • Adenoid hypertrophy; nasopharyngeal mass
  • Eustachian tube dysfunction
  • Neuromuscular disease
  • Family history/heredity
  • Prematurity and low birth weight
  • Craniofacial abnormalities (e.g., cleft palate, Down syndrome)
  • Third mobile window (superior canal dehiscence or large vestibular aqueduct)
• Sensorineural:
  • Aging/Older age
  • Loud noise/Acoustic trauma
  • Dizziness/Vertigo: Especially Ménière disease or history of labyrinthitis
  • Medications (aminoglycosides, loop diuretics, quinine, aspirin, chemotherapeutic agents)
  • Bacterial meningitis
  • Head trauma
  • Atherosclerosis
  • Vestibular schwannoma/skull base neoplasm
  • Previous ear surgery
• Sensorineural, pediatric-specific:
  • Postnatal asphyxia
  • Mechanical ventilation lasting ≥5 days
  • In utero infections (TORCH)
  • Toxemia of pregnancy
  • Maternal diabetes
  • Rh incompatibility
  • Prematurity or birth weight <1,500 g
  • Hyperbilirubinemia; exchange transfusions
  • Anomalous temporal bone (Mondini or large vestibular aqueduct)
  • Infectious diseases: Chickenpox, measles, encephalitis, influenza, mumps

• Connexin 26 (13q11–12): Most common cause of nonsyndromic genetic hearing loss
• Mitochondrial disorders (may predispose to aminoglycoside ototoxicity)
• Otosclerosis: Familial
• Most common congenital syndromes:
  • Hemifacial microsomia
  • Stickler syndrome
  • Congenital cytomegalovirus
  • Usher syndrome
  • Branchio-oto-renal syndrome
  • Pendred syndrome
  • CHARGE association
  • Neurofibromatosis type II
  • Waardenburg syndrome

General Prevention

• Limit noise exposure; use hearing protection.
• Avoid ear canal instrumentation (e.g., Q-tips).
• Limit ototoxic medications.

Pathophysiology

• CHL: Hearing loss can result from middle ear effusion, obstruction of canal (cerumen/foreign body, osteomas/exostoses, cholesteatoma, tumor), loss of continuity (ossicular discontinuity), stiffening of the components (myringosclerosis, tympanosclerosis, and otosclerosis), and loss of the pressure differential across the TM (perforation).
• SNHL: Damage along the pathway from oval window, cochlea, auditory nerve, and brain stem. Examples include vascular/metabolic insult, mass effect, infection and inflammation, acoustic trauma (see below):
  • Noise-induced hearing loss is caused by acoustic insult that affects outer hair cells in organ of Corti causing them to be less stiff. Over time, severe damage occurs with fusion and loss of stereocilia. Eventually may progress to inner hair cells and auditory nerve as well.

• Large vestibular aqueduct or superior canal dehiscence: Third mobile window shunts acoustic energy away from cochlea.