ENT (Otorhinolaryngology) · MU Sofia

6. Classifications and types of hearing loss.

Covers the three main types of hearing loss: conductive, sensorineural and mixed, setting out for each its site of damage, audiometric findings, symptoms and common causes. It then grades severity by pure-tone average in a table, describes audiogram configurations such as sloping, rising and cookie-bite, and closes with onset, time course and laterality classifications.

Inside: 1 section · 1 labelled picture · 1 table · 15 flashcards · 5 min

Topic 6 of 52 in the MU Sofia syllabus for ENT (Otorhinolaryngology) (Medicine, Year 4). The free AceMed note covers it in 1 section, about 724 words (5 min of reading), with 15 flashcards.

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  1. Classifications and Types of Hearing Loss

Classifications and Types of Hearing Loss

1. Conductive Hearing Loss (CHL) - CHL occurs when sound transmission is disrupted in the outer or middle ear, preventing sound energy from efficiently reaching the inner ear (cochlea).

  • Pathophysiology: A problem in the external ear canal, tympanic membrane, or ossicles (malleus, incus, stapes).
  • Key Audiometric Finding: Presence of an Air-Bone Gap (ABG) on the audiogram, typically defined as the difference between air conduction and bone conduction thresholds being greater than 10 to 15dB Hearing Level (HL) at one or more frequencies, with normal bone conduction thresholds. Negative Rinne’s test with lateralisation to affected ear in Weber’s test.
  • Symptoms: Sounds are perceived as simply muffled or too soft, often with the sensation of a "plugged" ear. The patient's own voice may sound louder (autophony). Patient hears better in noisy environment.
  • Common Causes:
  • Outer Ear: Cerumen (earwax) impaction, foreign body, otitis externa, congenital atresia (absence/closure of the ear canal).
  • Middle Ear: Otitis media (fluid in the middle ear) perforated tympanic membrane, ossicular chain discontinuity, otosclerosis (abnormal bone growth fixing the stapes), Eustachian tube dysfunction.

2. Sensorineural Hearing Loss (SNHL) - SNHL occurs due to damage to the inner ear (cochlea), which houses the sensory hair cells, or the auditory nerve (Cranial Nerve VIII), which transmits the signal to the brain. Patient hears better in noisy environment.

  • Pathophysiology: Damage to the hair cells of the cochlea (sensory loss) or the vestibulocochlear nerve (neural loss).
  • Key Audiometric Finding: Air and bone conduction thresholds are equally depressed (abnormal) with no significant Air-Bone Gap. Positive Rinne’s test with lateralisation to the unaffected ear in Weber’s test.
  • Symptoms: Sounds are not only softer but also often distorted or unclear, especially in background noise (poor speech discrimination). High-pitched sounds are frequently affected first. Tinnitis is common.
  • Common Causes:
  • Aging (Presbycusis): Most common cause, gradual high-frequency loss.
  • Noise Exposure: Acute or chronic exposure damaging the outer hair cells.
  • Ototoxicity: Drugs like aminoglycoside antibiotics, loop diuretics, and some chemotherapy agents.
  • Infections: Viral (e.g., Mumps, Measles, CMV, Labyrinthitis) or Bacterial (e.g., Meningitis).
  • Genetics: Syndromic (e.g., Usher, Pendred) or non-syndromic.
  • Other: Ménière's disease, head trauma, Vestibular Schwannoma (Acoustic Neuroma).

3. Mixed Hearing Loss (MHL) - MHL is a combination of CHL and SNHL, meaning pathology exists in both the sound-conducting pathway (outer/middle ear) and the sensory/neural pathway (inner ear/auditory nerve).

  • Pathophysiology: Simultaneous damage to both the conductive and sensorineural parts of the auditory system.

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