Conductive Vs. Sensorineural Hearing Loss

Overview

Snapshot

• A 30-year-old woman presents to her primary care physician due to worsening hearing loss of the right ear. This has never happened before and she denies any trauma to the ear. She has also noticed ear ringing of the right ear. Medical history is unremarkable. Family history is significant for her father undergoing surgery of the ear due to hearing loss. On physical exam, a conductive hearing loss is noted on Weber and Rinne testing. (Otosclerosis)

Introduction

• Hearing loss
  • basic principles
    • unilateral hearing loss can result from lesions affecting the
      • external auditory canal
      • middle ear
      • cochlear
      • cranial nerve VIII
      • cochlear nuclei
    • bilateral hearing loss suggests
      • a lesion after the auditory pathways enter the brainstem
        • this is because auditory information crosses bilateraly immediately after entering the brainstem
  • hearing loss is generally divided into
    • conductive hearing loss
      • secondary to lesions affecting the
        • external auditory canal
        • middle ear
    • sensorineural hearing loss
      • secondary to lesions affecting the
        • cochlea 
        • cranial nerve VIII
• Conductive hearing loss
  • etiologies include
    • otitis externa
    • squamous cell carcinoma
    • osteoma
    • cerumen
    • otitis media
    • cholesteatomoa
    • otosclerosis
    • tympanic membrane perforation
• Sensorineural hearing loss
  • etiologies include
    • hereditary hearing loss
    • presbycusis
      • age-related, high-frequency hearing loss caused by hair cell damage marked by stereocilia dysfunction 
    • ototoxic drugs
    • Meniere disease
    • barotrauma
    • acoustic neuroma
    • multiple sclerosis
• Physical exam maneuver
  • Rinne test
    • compares air conduction to bone conduction
      • air conduction is tested by
        • placing the vibrating tuning fork by the outside of the ear
      • bone conduction is tested by
        • placing the tuning fork on the mastoid process
    • normal findings are
      • air conduction is more than bone conduction
    • pathology
      • in conductive hearing loss
        • bone conduction is greater than air conduction
          • this is because bone conduction bypasses issues involving the external and middle ear
      • in sensorineural hearing loss
        • air conduction is greater than bone conduction bilaterally (just like in normal conditions)
        • there is decreased hearing in the affected ear
  • Weber test
    • the vibrating tuning fork is placed in the middle of the patient’s forehead
      • the patient is subsequently asked to say which side is loudest
    • normal findings
      • sound is equally heard in both ears
    • pathology
      • in conductive hearing loss
        • the tone is louder on the affected side
          • this is because of compenstatory mechanism aimed at increasing the perceived volume of the affected side
      • in sensorineural hearing loss
        • the tone is decreased on the affected side