Classify hearing loss and describe its causes and clinical assessment.

Types of Hearing Loss

• Hearing loss is classified by the site of the lesion into conductive, sensorineural, mixed, central and functional (non-organic).
• Establishing the type precedes establishing the cause, and it can be done with a tuning fork.
• Conductive loss arises anywhere from the pinna to the stapes footplate — the sound-conducting apparatus. The cochlea is normal, so bone conduction is normal and there is an air-bone gap

Causes

Clinical Approach

• The history should establish — which ear and whether both; the onset (sudden, rapid or gradual); the course (progressive, fluctuating or stable); and associated symptoms
• The pattern of onset is highly discriminating: sudden loss suggests vascular, viral, trauma or a perilymph fistula; fluctuating loss suggests meniere disease or a large vestibular aqueduct; slowly progressive suggests presbycusis, otosclerosis or a schwannoma
• Ask about discharge, pain, tinnitus, vertigo and facial weakness; about noise exposure at work and in recreation; about ototoxic drugs by name (aminoglycosides, furosemide, cisplatin, high-dose aspirin).
• Two questions are worth asking specifically: "Can you use the telephone on that side?", which uncovers a unilateral loss the patient has not noticed; and "Is it worse in a noisy room?", which suggests a cochlear or central problem rather than a conductive one
• Paracusis willisii — hearing better in noisy surroundings — is characteristic of otosclerosis and of conductive loss generally.
• Examination — otoscopy after clearing the canal; tuning fork tests; the facial nerve; the nose, postnasal space and throat; and cranial nerves and cerebellar signs where a schwannoma is possible
• Investigation — pure tone audiometry with masking; tympanometry and acoustic reflexes; speech audiometry; otoacoustic emissions and BERA; and imaging — CT for bone and middle ear disease, and MRI with gadolinium of the internal acoustic meatus for any asymmetric sensorineural loss
• The rule that must not BE forgotten: an asymmetric or unilateral sensorineural loss, or unilateral tinnitus, requires MRI to exclude a vestibular schwannoma — however plausible the alternative explanation seems
• Assess the disability, not only the audiogram — the effect on work, on family life and on safety.
• The maximum conductive loss is 60 decibels, so a greater loss proves a sensorineural component whatever the drum looks like
• A unilateral sensorineural loss is never central, because the pathway is bilateral above the cochlear nuclei
• Any asymmetric sensorineural loss needs an MRI of the internal acoustic meatus, however plausible the alternative explanation
• Otitis media with effusion is the commonest cause in children, and presbycusis much the commonest overall
• Otosclerosis is the commonest progressive conductive loss in a young adult with a normal drum and no history of ear disease