What decibel difference indicates asymmetrical hearing loss?

Defining Asymmetrical Hearing Loss by Decibel Difference

Asymmetrical sensorineural hearing loss (ASNHL) is defined as ≥10 dB interaural difference at 2 or more contiguous frequencies or ≥15 dB at any single frequency, with ≥15 dB at 3000 Hz having the highest positive predictive value for pathology such as vestibular schwannoma. 1, 2

Multiple Definitions in Clinical Practice

Several established definitions of asymmetrical hearing loss exist in clinical guidelines:

1. American Academy of Otolaryngology-Head and Neck Surgery and Congress of Neurological Surgeons criteria:

   • ≥10 dB interaural difference at 2 or more contiguous frequencies
   • ≥15 dB interaural difference at any single frequency
   • ≥15 dB interaural difference at 3000 Hz (highest positive predictive value) 1, 2

2. Alternative definitions in clinical practice:

   • ≥15 dB at 2 or more frequencies, or ≥15% difference in speech recognition score 1
   • ≥20 dB at 2 contiguous frequencies, or ≥15 dB at any 2 frequencies between 2000-8000 Hz 1
   • ≥10 dB at 2000 Hz for those with history of loud noise exposure (e.g., military) 1
   • ≥15 dB at 1000 Hz (84% sensitivity for abnormal MRI findings) 3

Clinical Significance and Diagnostic Implications

The definition of asymmetrical hearing loss is critical because:

• Pathology detection: Asymmetrical hearing loss warrants further evaluation for retrocochlear pathology, particularly vestibular schwannoma 1
• Diagnostic yield: Using the ≥10 dB at 2+ contiguous frequencies or ≥15 dB at any frequency criteria yields approximately 2-3% detection rate for vestibular schwannoma 1, 2
• MRI indication: Asymmetrical hearing loss meeting these criteria is an indication for MRI of the internal auditory canals 1, 2

Practical Application

When evaluating audiometric results:

• Most sensitive approach: Use ≥10 dB difference at 2+ contiguous frequencies or ≥15 dB at any frequency
• Most specific approach: Focus on ≥15 dB difference at 3000 Hz (highest positive predictive value) 1
• Speech recognition: Consider ≥15% difference in speech recognition scores between ears as significant asymmetry 1, 2

Important Caveats

• Any asymmetry must exceed 10 dB to be considered significant, as this exceeds the range of error for most audiograms 1
• Age-related hearing loss should be symmetric; asymmetry warrants further investigation 1
• In children, asymmetrical losses are more common and the degree of asymmetry at each frequency is typically more extensive than in adults 4, 5
• The diagnostic yield of MRI for asymmetric hearing loss is relatively low (2-3%), but the consequences of missing a vestibular schwannoma can be significant 1, 2

When asymmetrical hearing loss is identified using these criteria, MRI of the internal auditory canals is recommended to rule out retrocochlear pathology, particularly vestibular schwannoma 1, 2.