What are the different types and classifications of hearing loss?

Classification and Types of Hearing Loss

Hearing loss is classified into three fundamental types: conductive, sensorineural, and mixed—a distinction that is critical because each type has completely different management strategies and time-sensitive treatment implications. 1

Primary Classification System

Conductive Hearing Loss (CHL)

Conductive hearing loss results from abnormalities of the external ear, tympanic membrane, middle ear air space, or ossicles—the structures that conduct sound waves to the cochlea. 1

• Common causes include cerumen impaction, foreign bodies, stenosis, atresia, tympanic membrane perforation, middle ear effusion, cholesteatoma, ossicular discontinuity or fixation, and otosclerosis. 2
• The prognosis is generally favorable, as many causes are medically or surgically correctable. 2
• Otoscopic examination typically reveals visible abnormalities such as middle ear effusion, tympanic membrane retraction, or cerumen impaction. 2, 3

Sensorineural Hearing Loss (SNHL)

Sensorineural hearing loss results from abnormalities of the cochlea, auditory nerve, or other structures that translate neural impulses to the auditory cortex of the brain. 1

• This involves damage to hair cells in the cochlea, auditory nerve, or central auditory centers. 1, 2
• Age-related hearing loss (presbycusis) is the most common type in adults, affecting 1 in 3 adults aged 65-74 and nearly 50% of those over 75 years. 4, 2
• Presbycusis is characterized by bilateral and symmetric presentation, gradual and progressive course, high-frequency hearing loss pattern, and primary pathology of hair cell degeneration. 4
• Otoscopic examination is almost always normal in SNHL, unlike conductive hearing loss. 3
• SNHL is usually permanent, and management focuses on amplification and rehabilitation rather than cure. 2

Mixed Hearing Loss

Mixed hearing loss is a combination of both conductive and sensorineural hearing loss occurring in the same ear. 1

• This involves dysfunction in both the sound conduction pathway and the sensorineural components. 4, 2
• Management must address both components, often requiring surgical correction of the conductive element followed by amplification for residual sensorineural loss. 2

Severity Classification

The American College of Medical Genetics and Genomics defines six distinct severity categories based on pure tone average thresholds: 4

• Normal hearing: ≤20 dB HL
• Slight: 16-25 dB (may go unrecognized but impacts communication in challenging environments)
• Mild: 26-40 dB
• Moderate: 41-55 dB
• Moderately severe: 56-70 dB
• Severe: 71-90 dB
• Profound: ≥91 dB

Apply this classification to the better-hearing ear to accurately reflect functional hearing status. 4

Critical Clinical Distinctions

Sudden Sensorineural Hearing Loss (SSNHL)

SSNHL is defined as a decrease in hearing of ≥30 dB affecting at least 3 consecutive frequencies occurring within a 72-hour window. 1

• This represents a potential otologic emergency requiring immediate evaluation. 2
• Approximately 90% of cases are idiopathic (ISSNHL) after adequate investigation. 1
• Corticosteroids are most effective within 2 weeks of symptom onset—this is a time-sensitive treatment window. 2

Asymmetric Sensorineural Hearing Loss

Asymmetric SNHL requires immediate specialized evaluation as it may indicate serious underlying pathology such as vestibular schwannoma or meningioma. 4, 2

• MRI of brain and internal auditory canals should be obtained to rule out retrocochlear pathology. 2

Hidden Hearing Loss (Cochlear Synaptopathy)

This manifests as difficulty understanding speech in noise despite normal audiograms, affecting 5-15% of adults seeking audiologic help with normal hearing thresholds. 4

Diagnostic Differentiation

Clinicians must distinguish SNHL from CHL in every patient presenting with hearing loss—this is a strong recommendation because the two conditions have markedly different management strategies. 1

Physical Examination Findings

• Weber test: Sound lateralizes to the ear with CHL or away from the ear with SNHL. 3
• Rinne test: Air conduction is normally better than bone conduction; if bone conduction is better, CHL is present. 3
• Patients cannot accurately distinguish subjective hearing loss as either CHL or SNHL based on symptoms alone. 1, 3

Key Clinical Pitfall

Patients with SSNHL often report tinnitus, ear fullness or pressure, and vertigo—but these symptoms may also be present in CHL, making physical examination and audiometry essential rather than relying on history alone. 1, 3