What causes a low‑frequency hearing dip at 500 Hz?

Causes of Low-Frequency Hearing Dip at 500 Hz

A hearing dip at 500 Hz is most commonly caused by Ménière's disease when sensorineural, or by middle ear effusion/cerumen impaction when conductive—and you must first exclude the reversible conductive causes through otoscopy and tympanometry before pursuing any sensorineural diagnosis. 1

Immediate Diagnostic Steps

First, perform otoscopy and remove any cerumen impaction, as this is the most readily reversible cause of low-frequency hearing loss and must be excluded before establishing any other diagnosis 1. Even modest cerumen can produce a false conductive pattern that confounds the entire clinical picture 2.

Next, perform Weber and Rinne tuning fork tests (256-512 Hz) to differentiate conductive from sensorineural loss 1, 2:

• Weber lateralizing to the affected ear or negative Rinne (bone > air) indicates conductive pathology 2
• Weber lateralizing to the better ear with positive Rinne bilaterally suggests sensorineural loss 2

Primary Conductive Causes

Middle Ear Effusion

• Otitis media with effusion selectively affects low frequencies including 500 Hz and is particularly common in children 3, 1, 4
• The average hearing loss from middle ear effusion is 28 dB, though 20% of affected children have thresholds >35 dB 3
• Tympanometry is essential to confirm middle ear dysfunction and distinguish this from sensorineural pathology 1, 4

Cerumen Impaction

• Must be the first consideration and excluded through direct visualization 1, 4
• Can produce conductive losses that mimic more serious pathology 2

Primary Sensorineural Causes

Ménière's Disease (Most Common)

Ménière's disease is the classic cause of isolated low-frequency sensorineural hearing loss and presents with a characteristic clinical syndrome 3, 4:

• Episodic vertigo (typically lasting 20 minutes to 12 hours) 3
• Fluctuating hearing loss affecting low- to mid-frequencies (≤2000 Hz initially) 3, 4
• Tinnitus and aural fullness in the affected ear 3, 1
• Typically unilateral initially, with asymmetric hearing loss between ears (≥15 dB difference in pure-tone average at 500,1000,2000 Hz) 3

Audiometry is mandatory for definitive diagnosis—you cannot diagnose Ménière's disease without documented sensorineural hearing loss on formal testing 3, 4. The hearing loss fluctuates, so testing during or shortly after an acute episode is most revealing 3.

Autoimmune Inner Ear Disease

• Presents with fluctuating bilateral hearing loss that may preferentially affect low frequencies 1
• Often accompanied by vertigo 1
• Consider when bilateral sudden or rapidly progressive loss occurs 2

Infectious Causes

• Syphilis can cause bilateral fluctuating hearing loss with low-frequency involvement 1
• Lyme disease presents with fluctuating bilateral audiovestibular symptoms 1
• Both require serologic testing when bilateral or recurrent patterns emerge 2

Secondary Considerations

Ototoxicity

• Aminoglycosides and cisplatin can cause sensorineural hearing loss that may initially affect lower frequencies before progressing to higher frequencies 1

Trauma

• Head or ear trauma is more frequently associated with 1000 Hz notches (c3-dip) than with classic noise-induced 4000 Hz notches 5
• Recent acoustic or barotrauma should prompt evaluation for central pathology 2

Genetic/Metabolic

• Certain genetic mutations produce "cookie-bite" or U-shaped audiometric configurations with preserved mid-frequency hearing 4
• Diabetes increases risk of both high-frequency and low- to mid-frequency hearing impairment approximately two-fold through cochlear microangiopathy 4

Mandatory Diagnostic Workup

Obtain complete audiometry within 14 days including 3, 1, 4:

• Air and bone conduction thresholds at 250-8000 Hz
• Speech recognition thresholds and word recognition scores
• Mid-octave frequencies (750,1500 Hz) if differences between 500 and 1000 Hz exceed 20 dB 1, 4

Perform tympanometry to assess middle ear function and rule out conductive components 1, 4.

Order MRI with gadolinium of the internal auditory canals and posterior fossa for all confirmed asymmetric sensorineural hearing loss to exclude vestibular schwannoma and other retrocochlear pathology 3, 1, 2, 4. This is non-negotiable for asymmetric losses.

Critical Pitfalls to Avoid

• Never assume sensorineural loss without first excluding and treating cerumen impaction 1, 4
• Do not diagnose Ménière's disease without documented audiometric evidence of fluctuating sensorineural hearing loss 3
• Tuning fork tests cannot replace formal audiometry—they have limited sensitivity for mild losses and serve only as screening tools 2
• Standard test-retest variability is ±5 dB, so changes <10 dB may not represent true threshold shifts 1
• Bilateral sudden hearing loss demands aggressive workup including serologic testing (syphilis, HIV, autoimmune panel) and consideration of lumbar puncture if meningitis is suspected 2
• Word recognition scores worse than expected for the pure-tone average should prompt evaluation for retrocochlear pathology including auditory neuropathy or vestibular schwannoma 3

Age-Specific Considerations

In children aged 6 months to 4 years, comprehensive audiologic evaluation by an audiologist is required, using visual reinforcement audiometry (6 months to 2.5 years) or play audiometry (2.5 to 4 years) 3. Children under 3 years have "normal thresholds" up to 15 dB higher than adults due to developmental effects 3.

In adults with diabetes, screen for associated risk factors including low HDL cholesterol, coronary heart disease, and peripheral neuropathy, as these increase the likelihood of cochlear microangiopathy 4.