Hearing loss
Conductive hearing loss
- Mechanism by which sound is transformed and conducted to the cochlea is impaired
- Lesions involving the external or middle ear.
- Patients with conductive hearing loss maintain good ability to hear loud noises, and they hear better in the setting of noisy backgrounds.
- Aetiology
- Impacted cerumen in the external ear
- Inflammation of the middle ear (otitis media)
- Bony overgrowth and immobility of the stapes (otosclerosis).
Sensorineural hearing loss
- A deficit in the auditory pathway that occurs central to the oval window.
- Bilateral and progressive deafness: ototoxic drugs,
- Unilateral and progressive deafness: Meniere's disease or acoustic neuromas
- Unilateral and acute deafness: Viral infection or ischaemic infarction
- Characteristics
- Selective difficulty hearing high-pitched sounds and vowels.
- Formal audiometric testing of individuals with sensorineural hearing loss demonstrates a loss of speech discrimination that is out of proportion to associated pure-tone deafness.
- Difficulty hearing speech that is mixed with background noise.
- Pure tones may be distorted into a complex mixture of noisy, rough, or buzzing tones.
Genetic causes of hearing loss
- Alport syndrome
- Rare genetic disease
- Glomerulonephritis → end-stage kidney disease
- Hearing loss
- Can also affect the eyes (do not usually affect vision)
- Mechanism of Disease:
- Mutations in the type IV collagen gene (forms glomerular basement membranes or GBM). → GBM doesn’t function properly →
- Blood or proteins can leak into your urine → Glomerulonephritis → end-stage kidney disease (hematuria, proteinuria)
- Type IV collagen is also present in your ears and eyes
- Vision
- Hearing loss
- Jervell Lange-Nielsen syndrome (JLNS):
- A rare autosomal recessive disorder
- With following features
- Congenita deafness
- Long QT syndrome
- Mechanism of Disease:
- Mutations in the KCNE1 and KCNQ1 genes → K channel that transports positively charged potassium ions out of cells stops working → slow delayed rectifier potassium current does not function → cells cannot get repolarized →
- Prolonged QT interval → arrhythmias → dizziness, blackouts, sudden death
- Severe sensorineural hearing loss
- From birth, affecting both ears
Meniere’s disease
- A rare disorder lifelong condition of the inner ear that causes episodes of vertigo (the sensation of spinning), and hearing problems
- Symptoms:
- Frequent recurring episodes of vertigo lasting between 20 minutes to a few hours
- Nausea and vomiting due to severe vertigo,
- Loss of balance,
- Fluctuating or progressive loss of hearing, ultimately leading to permanent loss of hearing, ringing in the ear (tinnitus), and a feeling of fullness or pressure in the ear
- Causes:
- Unknown
- Possible due to viral infection.
- Changes in the amount or constituents of endolymph (fluid in the inner ear) may contribute to the symptoms.
- Other possible causes include improper fluid drainage due to a blockage or abnormal structure, an abnormal immune response, allergies, migraines, and stress
- Mechanism of disease
- Disorder of the inner ear that
- Over-accumulation (due to over-production, decreased absorption, or mechanical obstruction) of endolymph in the labyrinth of the inner ear → interferes with the normal balance and hearing signals between the inner ear and the brain
- Diagnosis:
- Pure tone Audiometry
- Videonystagmography (VNG)
- Rotary-chair testing
- Vestibular evoked myogenic potentials (VEMP) testing
- Posturography
- Video head impulse test (vHIT)
- Electrocochleography (ECoG)
- Complete blood count (CBC)
- CT scan
- MRI
- Treatment:
- Medication
- Surgery
- Rehabilitation therapy to reduce episodes of vertigo and hearing loss.
Gain in Auditory processing (hallucinations)
- While hearing voices, especially if threatening or accusatory, is more likely to be due to psychiatric illness, organic disease can also result in auditory hallucinations.
- These may be musical in nature, and are associated with temporal pathology, often non-dominant.
Tinnitus
- “Ringing in the ears.
- Frequently associated with sensorineural hearing loss.
- Due to lesions in the middle or inner ear.
- May be
- Subjective
- Heard only by the patient In subjective tinnitus,
- Pitch
- Conductive hearing loss is usually associated with low-frequency tinnitus,
- Sensorineural hearing loss is usually associated with high-frequency tinnitus.
- Exception
- Meniere's syndrome, sensorineural hearing loss associated with low-frequency tinnitus
- Objective tinnitus
- Heard by both the patient and the examiner
- A disorder outside the auditory system.
- Aetiology
- Eustachian tube
- Ossicles
- Palate
- Cerebral vascular malformations or aneurysms.
- Pulse synchronous tinnitus
- CCF
- Dural AVF
- Glomus jugulare tumour
- Vascular lesion in petrous bone
- Carotid stenosis
- IIH
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