Types of Hearing loss

Types of Hearing Loss

Hearing loss is defined as an impairment of auditory function, which can range in severity from mild to moderate or  profound. The term “deafness” refers to a condition characterized by little to no hearing ability.

Classification of Hearing Loss

The World Health Organization (WHO) established a grading system for hearing loss in 1980. This system is based on pure tone audiometry, which measures the average hearing threshold at frequencies of 500, 1000, and 2000 Hertz in the better ear. The following table summarizes the WHO grading of hearing loss:

1.  

Types of Hearing Loss

Hearing loss can be categorized into several distinct types, each characterized by different underlying mechanisms and causes:

1. Conductive hearing loss 
2. Sensorineural hearing loss
3. Mixed hearing loss 
4. Non-organic/ Functional hearing loss
5. Central hearing loss

1. Conductive Hearing Loss

Conductive hearing loss arises from obstructions in the transmission of sound waves along the auditory pathway, which extends from the external ear to the cochlea, specifically at the stapediovestibular joint. Potential causes of conductive hearing loss include:

• External Ear: Obstructions such as earwax or foreign objects.
• Tympanic Membrane: Perforations or other abnormalities.
• Middle Ear: Presence of fluid or infections.
• Ossicles: Fixation or disruption of the ossicular chain.
• Eustachian Tube: Obstructions affecting pressure equalization.

2. Sensorineural Hearing Loss

Sensorineural hearing loss is the result of damage to the cochlea (sensory type) or the eighth cranial nerve and its central auditory pathways (neural type). This type of hearing loss can be further specified as:

• Retrocochlear Hearing Loss: Caused by lesions affecting the eighth nerve.
• Central Deafness: Resulting from lesions in the central auditory pathways.

3. Mixed Hearing Loss

Mixed hearing loss is characterized by the presence of both conductive and sensorineural components in the same ear. This type is identified by the presence of an air-bone gap, which indicates conductive loss, alongside impaired bone conduction, indicative of sensorineural loss. Mixed hearing loss may occur in conditions such as otosclerosis and chronic suppurative otitis media.

4. Functional Hearing Loss

Functional hearing loss, also referred to as non-organic hearing loss, is characterized by the exaggeration or feigning of hearing impairment. Various terms have been used to describe this phenomenon, including pseudo-hyperacusis, malingering, and factitious hearing loss. In many instances, individuals may possess an underlying organic hearing loss that is intentionally exaggerated. In other cases, particularly following trauma, the individual may entirely feign hearing loss. Given the potential presence of an organic component, functional hearing loss is best understood as an exaggerated hearing loss or a functional overlay to an existing organic loss.

5. Central Hearing Loss

Individuals with central hearing loss exhibit difficulties in processing distorted or unclear speech, particularly in the presence of background noise, such as in social settings. Although these individuals typically have normal pure-tone hearing thresholds and pass other hearing tests, they struggle to follow verbal instructions. These challenges are attributed to deficits in the processing of auditory information within the higher auditory pathways.

Conductive Hearing Loss

Conductive hearing loss occurs when there is an obstruction in the transmission of sound waves at any point from the external ear to the cochlea (stapediovestibular joint).

The following characteristics are typically associated with conductive hearing loss:

1. Negative Rinne test results, indicating that bone conduction (BC) is greater than air conduction (AC).
2. Weber test lateralizes to the poorer ear.
3. Normal absolute bone conduction levels.
4. Greater impact on low frequencies.
5. Hearing loss typically does not exceed 60 dB.
6. Speech discrimination remains good, making individuals with conductive hearing loss suitable candidates for hearing aid amplification.
7. Hearing loss is partial, as bone conduction remains intact.

Characteristics of Conductive Hearing Loss on Pure Tone Audiometry (PTA)

• A difference of more than 10 dB between AC and BC thresholds at any frequency.
• BC thresholds are generally at normal hearing levels (equal to or better than 20 dB HL) in cases of pure conductive hearing loss.
• If BC thresholds exceed 20 dB HL with a significant air-bone gap (ABG), this condition is classified as mixed hearing loss.

Causes of conductive hearing loss:

Management of Conductive Hearing Loss

Management strategies for conductive hearing loss include:

1. Removal of Canal Obstructions: This may involve addressing impacted cerumen, foreign bodies, osteomas, exostoses, keratotic masses, benign or malignant tumors, or meatal atresia.
2. Hearing Aids: These devices are utilized when surgical options are not feasible, are declined by the patient, or have previously failed.
3. Surgical Interventions:

1. • Myringotomy with or without grommet insertion to remove fluid from the middle ear.
   • Myringoplasty, which involves the surgical repair of the tympanic membrane.
   • Tympanoplasty is an operation to (i) eradicate the disease from the middle ear and (ii) to reconstruct the hearing mechanism with or without mastoid surgery, with or without tympanic membrane grafting.
   • Ossiculoplasty to reconstruct the ossicular chain.

 

SENSORINEURAL HEARING LOSS: Sensorineural hearing loss (SNHL) occurs when there is failure in the cochlear transduction (change in mechanical energy into electrical energy) process from going to neural impulses of the eighth nerve. It occurs due to damage or impairement in cochlea (sensory) or eighth cranial nerve (retrocochlear) and its central connections (central deafness). This causes reduction in the sensitivity of the cochlear receptor cells.

The characteristics of sensorineural hearing loss are:

1. A positive Rinne test, i.e. AC > BC.
2. Weber lateralized to the better ear.
3. Bone conduction reduced on Schwabach and absolute bone conduction tests.
4. There is poor speech discrimination which means that the patient is able to hear the speech but not able to understand it.
5. There is difficulty in hearing in the presence of noise.
6. Recruitment phenomenon (abnormal loudness growth) may be present.
7. Hearing loss may range from minimal to total and is usually permanent.
8. Usually treated with hearing aids or implants. Options for medical or surgical interventions are very limited.

The characteristics of sensorineural hearing loss on PTA:

1. AC and BC thresholds being within 10dB of each other.
2. High frequencies are mostly involved.
3. Loss may exceed 60 dB, generally complete hearing loss.

AETIOLOGY

Congenital. Congenital SN hearing loss may be due to inner ear anomaly or pre-natal/perinatal damage to hearing apparatus.

 

TABLE: Syndromes associated with SNHL (Congenital)

Acquired causes of SNHL. It develops later in life. It can be genetic type or non-genetic type. The genetic type may affect only hearing part (non-syndromic), or be a part of a syndrome affecting other systems of the body as well (syndromic).

Types of Hearing Loss Types of Hearing Loss Types of Hearing Loss Types of Hearing Loss Types of Hearing Loss Types of Hearing Loss Types of Hearing Loss Types of Hearing Loss Types of Hearing Loss Types of Hearing Loss Types of Hearing Loss Types of Hearing Loss Types of Hearing Loss Types of Hearing Loss Types of Hearing Loss Types of Hearing Loss Types of Hearing Loss Types of Hearing Loss Types of Hearing Loss

Common causes of acquired SNHL include:

1. Infections of labyrinth—viral, bacterial or spirochaetal
2. Noise-induced hearing loss
3. Ototoxic drugs
4. Presbycusis
5. Sudden hearing loss
6. Meniere’s disease Refer to page no.
7. Acoustic neuroma Refer to page no.
8. Trauma to labyrinth or VIIIth nerve.
9. Familial progressive SNHL
10. Systemic disorders, e.g. diabetes, hypothyroidism, kidney disease, autoimmune disorders, multiple sclerosis, blood dyscrasias.

S No.	Causes of Bilateral SNHL	Causes of Unilateral SNHL
1.	Presbycusis	CSOM
2.	Meniere’s disease	Mumps
3.	Otosclerosis	Herpes zoster oticus
4.	Noise-induced hearing loss	Acoustic neuroma

———— End of the chapter ————

Learning resources.

• Scott-Brown, Textbook of Otorhinolaryngology Head and Neck Surgery.
• Glasscock-Shambaugh, Textbook of  Surgery of the Ear.
• Logan Turner, Textbook of Diseases of The Nose, Throat and Ear Head And Neck Surgery.
• Rob and smith, Textbook of Operative surgery.
• P L Dhingra, Textbook of Diseases of Ear, Nose and Throat.
• Hazarika P, Textbook of Ear Nose Throat And Head Neck Surgery Clinical Practical.
• Mohan Bansal, Textbook of Diseases of Ear, Nose and Throat Head and Neck surgery.
• Anirban Biswas, Textbook of Clinical Audio-vestibulometry.
• W. Arnold, U. Ganzer, Textbook of  Otorhinolaryngology, Head and Neck Surgery.
• Salah Mansour, Textbook of Comprehensive and Clinical Anatomy of the Middle Ear.

Author:

Dr. Rahul Bagla

MBBS (MAMC, Delhi) MS ENT (UCMS, Delhi)
Fellow Rhinoplasty & Facial Plastic Surgery.
Renowned Teaching Faculty
Mail: msrahulbagla@gmail.com
India

Please read. Glomus Tumour. https://www.entlecture.com/glomus-tumour/

Follow our Facebook page: https://www.facebook.com/Dr.Rahul.Bagla.UCMS

Join our Facebook group: https://www.facebook.com/groups/628414274439500