Hearing impairment classification

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Classification

Hearing losses can be classified according to:

1. Laterality,
2. Symmetry,
3. Clinical characteristic (syndromic or not),
4. Time of onset (congenital, perinatal, or postnatal),
5. Hereditary (genetic or not),
6. Time of manifestation (prelingual, perilingual, or post-lingual),
7. Intensity (mild, moderate, severe, and profound)

CLASSIFICATION BASED OF SEVERITY OF DISEASE

	MILD	MODERATE	SEVERE	DISABLING
HEARING LOSS	26–40 dB HL	41–60 dB HL	61–80 dB HL	>80 dB HL
DESCRIPTION	Patient hears fine	Hear with some difficulty. People Mumble.	Difficulty in hearing.	Patients relies on reading lips. The term deaf is often used by persons with profound hearing loss with >80 dB HL.
INTERVENTION	Communication strategies	Communication strategies Amplification	Communication strategies Hearing aids Cochlear implant	Communication strategies Hearing aids Cochlear implant Sign language Lip reading

CLASSIFICATION BASED ON ANATOMY OF EAR

CONDUCTIVE	SENSORINEURAL	MIXED
CHL occurs when sound is not conducted efficiently through the external ear canal to the middle ear.	SNHL occurs when there is damage to the inner ear or to the nerve pathways from the inner ear to the brain. So loss at the point of the cochlea or proximal to the cochlea is considered SNHL.	Mixed HL is defined as CHL and SNHL.
CHL accounts for 90%–95% of all childhood HL.	SNHL is far more common in adults
Common causes in adults include: Cerumen impaction Otosclerosis Cholesteatoma Otitis media with effusion.	If SNHL takes hours or days to develop it can be due to: Labyrinthitis Meniere disease If hearing loss develops in weeks: Drug-induced ototoxicity If happens in years: Noise-induced loss

CLASSIFICATION BASED ON CAUSE

CONGENITAL

ACQUIRED

Syndromes Dysplasia: Children with skeletal dysplasias were more likely to have abnormal tympanometry, reflecting the greater likelihood of middle ear disease. Infections: Cytomegalovirus (CMV), rubella virus, Toxoplasma gondii, herpes virus, and HIV Malformations

Infections: Bacterial meningitis, particularly from Streptococcus pneumoniae, has been reported to be one of the most common postnatal causes of hearing loss in children. Traumatic Autoimmune: Systemic diseases that cause hearing loss include systemic lupus erythematosus, rheumatoid arthritis, myasthenia gravis, and Hashimoto's thyroiditis Neoplastic: Direct compression of the cochlear nerve by the tumor, occlusion or vascular compression of the internal auditory artery, intratumor bleeding, internal auditory canal occlusion, and toxic substances produced by the tumor that causes degeneration of the inner ear.

Conductive

Conductive hearing loss occurs when sound is not normally conducted through the outer or middle ear (or both). Since sound can be picked up by a normally sensitive inner ear even if the ear canal, ear drum, and ear ossicles are not working, conductive hearing loss is often only mild and is never worse than a moderate impairment. Hearing thresholds will not rise above 55-60 dB from outer or middle ear problems alone. Generally, with pure conductive hearing loss, the quality of hearing (speech discrimination) is good, as long as the sound is amplified loud enough to be easily heard.

A conductive loss can be caused by any of the following:

• Ear canal obstruction
• Middle-ear abnormalities
  • Tympanic membrane
  • Ossicles

Sensorineural

Main article: Sensorineural hearing loss

A sensorineural hearing loss is due to insensitivity of the inner ear (the cochlea), or to impairment of function in the auditory nervous system. It can be mild, moderate, or severe, including total deafness. This is classified as a disability under the ADA and if unable to work is eligible for disability payments.

The great majority of human sensorineural hearing loss is caused by abnormalities in the hair cells of the organ of Corti in the cochlea. There are also very unusual sensorineural hearing impairments that involve the VIIIth cranial nerve (the Vestibulocochlear nerve) or the auditory portions of the brain. In the rarest of these sorts of hearing loss, only the auditory centers of the brain are affected. In this situation, central hearing loss, sounds may be heard at normal thresholds, but the quality of the sound perceived is so poor that speech can not be understood.

Most sensory hearing loss is due to poor hair cell function. The hair cells may be abnormal at birth, or damaged during the lifetime of an individual. There are both external causes of damage, like noise trauma and infection, and intrinsic abnormalities, like deafness genes.

Sensory hearing loss (also called sensorineural hearing loss) may also result from abnormalities of the VIII cranial nerve.

Sensory hearing loss that results from abnormalities of the central auditory system in the brain is called Central Hearing Impairment. Since the auditory pathways cross back and forth on both sides of the brain, deafness from a central cause is unusual.