What are the diagnostic criteria for mixed hearing loss?

Diagnostic Criteria for Mixed Hearing Loss

Mixed hearing loss is diagnosed when both sensorineural hearing loss (SNHL) and conductive hearing loss (CHL) occur simultaneously in the same ear, requiring audiometric confirmation with both air and bone conduction testing showing abnormalities. 1

Core Diagnostic Definition

Mixed hearing loss (MHL) represents the coexistence of both conductive and sensorineural components affecting the same ear. 1, 2 This means:

• Conductive component: Pathology in the external auditory canal, tympanic membrane, or middle ear blocking sound conduction 1
• Sensorineural component: Dysfunction of the cochlea, auditory nerve, or central auditory pathways occurring simultaneously 1, 3

Audiometric Criteria

The diagnosis requires comprehensive audiometric testing demonstrating specific patterns 1, 2:

Pure Tone Audiometry Requirements

• Air conduction thresholds must be elevated (>20 dB HL in adults, >15 dB HL in children) 2, 4
• Bone conduction thresholds must also be elevated (>20 dB HL), confirming the sensorineural component 3, 5
• An air-bone gap must be present (typically ≥10 dB), confirming the conductive component 3, 5, 6
• Testing should span frequencies from 250-8000 Hz with both air and bone conduction measurements 1, 4

Speech Audiometry

• Speech recognition threshold (SRT) and word recognition scores (WRS) should be obtained to assess functional hearing ability 1, 5
• Poor word recognition scores disproportionate to pure tone average may indicate retrocochlear pathology requiring additional workup 1, 5

Physical Examination Findings

Unlike pure sensorineural hearing loss where otoscopy is typically normal, mixed hearing loss requires identifying conductive pathology 2:

• Otoscopic examination will show abnormalities: middle ear effusion, tympanic membrane retraction or perforation, cerumen impaction, cholesteatoma, or structural pathology 1, 2
• Tuning fork testing (Weber and Rinne tests) helps distinguish the mixed nature by demonstrating both conductive and sensorineural components 1, 2

Tympanometry Confirmation

• Tympanometry is essential for evaluating middle ear function and confirming the conductive component 1, 4
• Abnormal tympanograms (Type B or C) support middle ear pathology contributing to the conductive component 7

Critical Diagnostic Pitfalls

Asymmetric mixed hearing loss requires immediate specialized evaluation to rule out serious underlying pathology such as vestibular schwannoma or other retrocochlear lesions 1, 2. The American Academy of Otolaryngology-Head and Neck Surgery emphasizes that patients with conductive or mixed hearing loss should be referred for specialized management, as this represents a potentially serious clinical scenario 2.

Standard test-retest variability typically fluctuates by ±5 dB across frequencies, so changes <10 dB may not represent true threshold shifts 4, 8. This is important when monitoring progression or treatment response.

Severity Classification

Once mixed hearing loss is confirmed, severity is graded based on the better ear's pure tone average at 500,1000, and 2000 Hz 8:

• Slight: 16-25 dB 8
• Mild: 26-40 dB 8
• Moderate: 41-55 dB 8
• Moderately severe: 56-70 dB 8
• Severe: 71-90 dB 8
• Profound: ≥91 dB 8

Additional Workup Considerations

Temporal bone imaging (CT or MRI) should be considered as part of the comprehensive evaluation, particularly when surgical intervention is contemplated or when the etiology is unclear 1. CT with bone algorithms is optimal for evaluating conductive pathology, while MRI with gadolinium is preferred for assessing sensorineural components and ruling out retrocochlear pathology 3.