Hearing Loss

Essentials of Diagnosis

• Two main types of hearing loss

  • Conductive

  • Sensorineural

• Most commonly caused by cerumen impaction or transient auditory tube dysfunction from upper respiratory tract infection

General Considerations

Conductive loss

• Four mechanisms, each resulting in impairment of the passage of sound vibrations to the inner ear

  • Obstruction (eg, cerumen impaction)

  • Mass loading (eg, middle ear effusion)

  • Stiffness effect (eg, otosclerosis)

  • Discontinuity (eg, ossicular disruption)

• Generally more correctable than sensory and neural losses

Sensorineural loss

• Sensory and neural causes of hearing loss are difficult to differentiate due to testing methodology, thus often referred to as "sensorineural"

• Sensory loss

  • Most common form is a gradually progressive, predominantly high-frequency loss with advancing age (presbyacusis)

  • Other common causes include

    • Excessive noise exposure

    • Head trauma

    • Systemic diseases

  • Sensory hearing loss is usually not correctable but may be prevented or stabilized

  • However, sudden sensory hearing loss may respond to corticosteroids if delivered within several weeks of onset

• Neural loss

  • Occurs with lesions involving the eighth nerve, auditory nuclei, ascending tracts, or auditory cortex

  • It is the least common clinically recognized cause of hearing loss

  • Causes include

    • Acoustic neuroma

    • Multiple sclerosis

    • Cerebrovascular disease

Symptoms and Signs

• Reduction in hearing level

• Weber test

  • Tuning fork is placed on the forehead or front teeth

  • In conductive losses, the sound appears louder in the poorer hearing ear, whereas in sensorineural losses it radiates to the better side

• Rinne test

  • Tuning fork is placed alternately on the mastoid bone and in front of the ear canal

  • In conductive losses > 25dB, bone conduction exceeds air conduction, whereas in sensorineural losses, the opposite is true

Differential Diagnosis

Conductive (external or middle ear)

• Cerumen (ear wax) impaction

• Transient auditory tube dysfunction

• Acute or chronic otitis media

• Mastoiditis

• Otosclerosis

• Disruption of ossicles

• Trauma or barotrauma

• Glomus tympanicum (middle ear tumor)

• Paget disease

Sensory

• Presbycusis (age related)

• Excessive noise exposure

• Ménière disease (endolymphatic hydrops)

• Labyrinthitis

• Head trauma

• Ototoxicity

• Occlusion of ipsilateral auditory artery

• Hereditary hearing loss

• Autoimmune

  • Systemic lupus erythematosus

  • Granulomatosis with polyangiitis

  • Cogan syndrome

• Other systemic causes

  • Diabetes mellitus

  • Hypothyroidism

  • Hyperlipidemia

  • Chronic kidney disease

  • Infections

Neural

• Acoustic neuroma

• Multiple sclerosis

• Cerebrovascular disease

Diagnostic Procedures

• Formal audiometric studies are performed in a soundproofed room

• Pure-tone thresholds in decibels (dB) are obtained over the range of 250–8000 Hz for both air and bone conduction

• In conductive losses, there is a gap between the air and bone thresholds

• In sensorineural losses, both air and bone thresholds are equally diminished

• Speech discrimination measures the clarity of hearing, which is reported as percentage correct (90–100% is normal)

• Auditory brainstem-evoked responses may determine whether the lesion is sensory (cochlear) or neural (central)

Surgery

• The cochlear implant—an electronic device that is surgically implanted to stimulate the auditory nerve—offers socially beneficial auditory rehabilitation to most adults with acquired deafness

• Many types of conductive hearing loss (eg, otosclerosis, tympanic membrane perforation, ossicular discontinuity) are surgically remediable

• Hearing aids

  • An alternative strategy, the bone-anchored hearing aid, uses an oscillating post drilled into the mastoid, directly stimulating the ipsilateral cochlea (for conductive losses) or contralateral ear (profound unilateral sensorineural loss)

Therapeutic Procedures

• Hearing aids

• Assistive devices are available to improve comprehension in individual and group settings, to help with hearing television and radio programs, and for telephone communication

Follow-Up

• Routine audiologic screening is recommended for adults with prior exposure to potentially injurious levels of noise or in adults at age 65, and every few years thereafter

When to Refer

• Every patient who complains of a hearing loss should be referred for audiologic evaluation unless the cause is easily remediable (eg, cerumen impaction, otitis media)

• Immediate audiometric referral is indicated for patients with idiopathic sudden sensorineural hearing loss because it requires treatment (corticosteroids) within a limited several-week time period