Hearing loss

Background

• Sensorineural: involving the inner ear, cochlea, or auditory nerve
• Conductive: any mechanical factor blocking external sound from gaining access to the inner ear; ex: cerumen impaction, middle ear fluid, ossicular chain fixation
• Mixed: both sensorineural and conductive loss

Epidemiology

• Most common causes: presbycusis, followed by noise-induced hearing loss
• 90% of cases are due to Sensorineural hearing loss, 10% due to Conductive causes
• Most bilateral cases that present gradually are benign. Sudden onset, unilateral hearing loss is more concerning for a serious cause.

Differential Diagnosis

Sensorineural (Inner Ear)

• Sudden Sensorineural Hearing Loss (SSHL)
• Infections: (Meningitis, Viral cochleitis)
• Barotrauma
• Penetrating trauma
• Meniere Disease
• Autoimmune disease
• Multiple Sclerosis
• Cerebrovascular ischemia
• Tumors (Acoustic neuroma, Meningioma)
• Hereditary hearing loss
• Congenital viral infections
• Congenital malformations
• Presbycusis
• Thyrotoxicosis
• Ototoxic drugs: [{Aminoglycosides]], Erythromycin, Tetracycline, chemotherapeutic agents, high-dose aspirin, phosphodiesterase-5 inhibitors, antimalarial drugs, Cocaine, Heavy Metals
• Otologic surgery
• Noise exposure

Conductive

• Outer Ear
  • Trauma
  • Squamous cell carcinoma
  • Congenital microtia or atresia
  • Otitis Externa
  • Exostosis
  • Osteoma
  • Psoriasis
  • Cerumen Impaction
• Middle ear
  • Glomus tumors
  • Tympanic membrane perforation
  • Temporal bone trauma
  • Congenital atresia or Ossicular chain malformation
  • Eustachian tube dysfunction
  • Chronic Otitis media
  • Cholesteatoma
  • Otosclerosis

Evaluation

• History: Gather information on recent medication changes, family history of hearing loss, personal history of trauma, recent scuba diving or flying (barotrauma), cold water exposure, onset/progression of hearing loss, high- vs low-pitch loss, history of ear surgeries, other medical history
• Whispered voice test: Stand at arm’s length behind the patient and block hearing in one ear by occluding the ear canal. Whisper a phrase and ask the patient to repeat it. Test both ears.

• Tone-emitting otoscope: Designed to view the ear canal and TM while emitting three different screening levels at random intervals.

Weber test

A vibrating tuning fork is placed on the tip of the forehead, nose, or teeth. If the patient hears the sound equally in both ears, normal hearing or symmetric hearing loss is suspected. If the bad ear hears less sound than the other, that ear is suspected to have sensorineural hearing loss. If the bad ear hears sound better than the good ear through this test, the bad ear is suspected to have conductive hearing loss.

Rinne test

A vibrating turning fork is placed on the mastoid bone behind the ear. When the sound is no longer heard, the fork is held near the ear canal. If the sound is still present or louder at the ear canal, normal hearing is suspected. Thus, air conduction is greater than bone conduction. If no sound is heard near the ear canal but the sound was still heard on the mastoid bone, conductive hearing loss is suspected in that ear. In this case, bone conduction is greater than air conduction.

• Examination of auricle and external ear canal to look for blockage; view TM to ensure no fluid collection or TM perforation.

Pneumoscopy

• To evaluate mobility of the TM.

1. First, use positive pressure to force air into the EAC to push down the TM.
2. Then, release the pressure and the negative pressure pulls the TM outwards.
   • Nonmobile = fluid in middle ear, mass in middle ear, stiff/sclerotic TM.
   • Hypermobile TM = ossicular chain disruption.
   • Movable TM only with negative pressure = blocked Eustachian tube.

Formal audiologic assessment

• Performed by an audiologist in a soundproof environment. Air and bone conduction are both tested.
  • Speech audiometry: The speech reception threshold (SRT), which is the softest level that a patient can correctly repeat at least half of the words presented, is measured. The word discrimination score gives a percentage of words that a patient can correctly repeat at a given sensation level.
  • Impedance audiometry: Tympanometry and stapedial reflex testing.

Other tests

Consideration for these tests should be based on history and physical

• Blood sugar
• CBC to evaluate for anemia or infection
• Thyroid testing
• Serologic testing for Syphilis, Sjogren’s syndrome
• CT scan for unexplained conductive hearing loss
• MRI for sensorineural hearing loss
• ENT evaluation for presbycusis

Management

• Based on exam findings and imaging.

References

• Weber PC. Sudden sensorineural hearing loss. In: UpToDate. Accessed Sept 22 2014.
• Weber PC. Etiology of hearing loss in adults. In: UpToDate. Accessed Sept 22 2014.
• Molina, FJ. Hearing Loss, Chapter 18. Tintinalli’s Emergency Medicine.