What causes low and high frequency hearing loss?

Causes of Low and High Frequency Hearing Loss

High-Frequency Hearing Loss

High-frequency hearing loss primarily results from degeneration of outer hair cells at the basal turn of the cochlea, with noise exposure causing irreversible neural damage even when hearing thresholds appear to recover. 1

Primary Mechanisms

• Noise-induced cochlear synaptopathy causes permanent, progressive neural damage that selectively affects high-threshold auditory nerve fibers with low spontaneous rates, even after temporary threshold shifts resolve 1
• This "hidden hearing loss" involves extensive loss of synaptic connections between inner hair cells and auditory nerve terminals, followed by degeneration of spiral ganglion cells months to years later 1
• The outer hair cells at the basal turn of the cochlea (responsible for high-frequency detection) are the primary site of noise-induced lesions 2, 1

Age-Related Mechanisms

• Sensory presbycusis involves degeneration of hair cells starting at the basal turn (high-frequency region), which can begin prematurely in susceptible individuals 1
• Neural presbycusis causes loss of cochlear neurons, affecting speech discrimination and high-frequency detection 1
• Age-related hearing loss presents initially with increased hearing thresholds at higher frequencies but progresses at variable rates to impact midrange and lower frequencies over time 2
• High-frequency hearing loss increases with aging, rising more rapidly in men than women 2, 1

Contributing Risk Factors

• Chronic medical conditions including diabetes (2-fold increased prevalence of hearing loss), hypertension, and hypercholesterolemia influence development of hearing loss 2
• Ototoxic medications including aminoglycosides, cisplatin, loop diuretics (furosemide), and phosphodiesterase-5 inhibitors (tadalafil) cause sensorineural hearing loss 3
• Smoking and passive smoke exposure have deleterious effects on hearing 2
• Genetic factors account for approximately half the variance in age-related hearing loss 4

Critical Clinical Pitfall

• 5-15% of adult patients seeking audiologic help have normal hearing thresholds but suffer from cochlear synaptopathy causing difficulty understanding speech in background noise 1
• Standard audiometry may miss early neural damage that manifests as "hidden hearing loss" with preserved thresholds 1
• Assuming temporary threshold shifts are benign is dangerous—they actually predispose the auditory system to premature neural aging and progressive damage 1

Low-Frequency Hearing Loss

Ménière's disease is the classic cause of isolated low-frequency hearing loss, presenting with a characteristic low-frequency trough on audiometry and fluctuating hearing loss. 5

Primary Causes

• Ménière's disease presents with isolated low-frequency hearing trough on audiometry, characterized by fluctuating hearing loss affecting one or both sides, with episodes of vertigo 5, 6
• In Ménière's disease, the whole cochlear sensory area is affected, with damage advancing simultaneously in all parts of the cochlea, though greatest at 0.5-1 kHz 6
• Autoimmune inner ear disease presents with fluctuating bilateral hearing loss that may preferentially affect low frequencies, often accompanied by vertigo 5
• Conductive pathology such as cerumen impaction or middle ear fluid can mimic low-frequency hearing loss and must be excluded through otoscopy 5

"Inner Ear" Conductive Component

• Some patients with Ménière's disease demonstrate an unexplained low-frequency air-bone gap (32.5% in one study) without middle ear pathology 7
• This "inner ear" conductive hearing loss may result from endolymphatic hydrops or perilymphatic hypertension exerting pressure against the stapedial footplate medially 7

Secondary and Systemic Causes

• Infectious causes including syphilis (bilateral fluctuating hearing loss), Lyme disease (fluctuating bilateral audiovestibular symptoms), and meningitis (bilateral hearing loss) 5
• Ototoxic medications can cause sensorineural hearing loss that may initially affect lower frequencies 5
• Genetic disorders may be syndromic or nonsyndromic with variable audiometric patterns 5

Diagnostic Approach

• Antecedent fluctuating hearing loss on one or both sides strongly suggests Ménière's disease or autoimmune causes 5
• Perform otoscopy to exclude conductive causes such as cerumen impaction or middle ear fluid before establishing sensorineural diagnosis 5
• Conduct Weber and Rinne tuning fork tests to differentiate conductive from sensorineural loss 5
• Consider recent viral illness, bacterial meningitis, or exposure to ototoxic medications in the patient's history 5

Critical Clinical Pitfalls

• Failing to remove cerumen before establishing diagnosis can lead to misdiagnosis of sensorineural loss when conductive loss is present 5
• Assuming all low-frequency loss is Ménière's disease without considering autoimmune, infectious, or ototoxic causes 5
• Missing bilateral presentation, which should prompt evaluation for systemic causes including autoimmune disease, infection, or ototoxicity 5