Etiology

Infections

• Otitis externa Otitis externa  /media Otitis media  /interna Otitis interna.

Ototoxicity

• Drugs or chemicals that damage either the sensory hair cells in the cochlea, or the stria vascularis.
• Include: aminoglycosides, diuretics, eg furosemide Furosemide, antineoplastic drugs, eg vincristine Vincristine, other antibiotics, eg erythromycin Erythromycin, topical antiseptics, eg cetrimide and various other agents, eg ceruminolytics, prednisolone Prednisolone, salicylates  Acetyl salicylic acid, detergents. Ototoxicity of compounds varies greatly. Effect may be compounded by simultaneous use of two drugs at correct dosage eg loop diuretics and aminoglycosides.

Presbycusis

• Ageing.

Trauma

• Physical or acoustic (selective frequency deafness).

Fetal

• Intrauterine infection, toxicity, anoxia.

Pathophysiology

• Occlusion of external ear canal.
• Destruction of tympanic membrane and structures of middle ear.
• Damage to anatomy of inner ear.
• Sensorineural deficits.

• Otitis externa   →   stenotic external canal occluded with cerumen   →   conductive deafness.
• Otitis media/interna   →   destruction of tympanic membrane and middle ear structures   →   conductive deafness.
• Hemotogenous or exogenous infection   →   labyrinthitis (inflammation of inner ear)   →   sensorineural deafness. Associated vestibular deficits Vestibular disease.
• Systemic aminoglycoside toxicity   →   theory: drug binds to glycosaminoglycans in stria vascularis of cochlear canal   →   disrupts phosphoinositide metabolism   →   sequential and progressive destruction of cochlear hair cells.
• Topical application toxicity with ruptured tympanum   →   drug reaches inner ear   →   absorbed into cochlea. It has been suggested that topical applications according to recommended dosage even where the tympanum is ruptured can be assumed to be safe, although this is not guaranteed. Ototoxicity of drugs may be increased by anesthesia, previous cochlear damage, age and infection. Successive courses of treatment may have a cumulative effect.
• Presbycusis   →   progressive pathology of middle ear structures   →   impaired articulation between tympanum and ossicles.
• Acoustic trauma   →   increased shearing force   →   breaks cochlear hairs. May damage tympanic membrane and ossicles.