Deafness

Impaired perception of acoustic signals.

Diagnosis

Often the diagnosis is obvious or can be confirmed by a simple hearing test. More subtle hearing impairments can be measured audiometrically, which also allows to distinguish different types of deafness. Objective audiometry, which uses EEG signals to confirm acoustic signal perception, is available for small children, mentally disabled, and notorious liars.

Pathogenesis

Deafness may be hereditary or acquired. The latter is mostly due to a chronic noise trauma and called loud noise deafness. Congenital deafness, when results from malformation, often exists right from birth. However, hereditary deafness may also develop with age. Then it is often due to disturbed metabolism or regeneration and difficult to distinguish from acquired forms.

Classification

According to the site of damage deafness may be divided into conductive, sensorineural, and mixed. In conductive deafness the conduction of sonic waves onto the cochlea is blocked. Sensorineural deafness is either due to a cochlear or retrocochlear lesion. We further distinguish symmetrical and asymmetrical hearing loss. Audiometric measurement allows to distinguish high frequency deafness.

Diseases

Alport Syndrome
	Progressive sensorineural deafness occurs in about 75% of cases.
Branchiootic syndrome
	Branchiootic syndrome deafness is of a mixed (conductive and sensorineural) type because of malformations (atresia to stenosis) of the external auditory canal and nderdeveloped cochlea and semicircular canals, respectively.
Branchiootorenal dysplasia
	Branchiootorenal dysplasia deafness is of a mixed (conductive and sensorineural) type because of malformations (atresia to stenosis) of the external auditory canal and nderdeveloped cochlea and semicircular canals, respectively.
EAST syndrome
	Sensorineural deafness in EAST syndrome results from endolyphatic electrolyte dysbalance.
Hypoparathyroidism, sensorineural deafness, and renal dysplasia syndrome
	Sensorineural deafness may occur with GATA3 mutations.
Infantile Bartter syndrome with deafness type 4
	Sensorineural deafness in infantile Bartter syndrome results from endolyphatic electrolyte dysbalance.
Muckle-Wells syndrome
	A late-onset sensorineural deafness is typical of Muckle-Wells syndrome.
MYH9 related disorders
	Sensorineural deafness is typical of MYH9 mutations.
Distal renal tubular acidosis with deafness (autosomal recessive)
	Sensorineural deafness is typical of ATP6V1B1 mutations.
X-linked dominant hypophosphatemic rickets
	Hearing loss is not a symptom of X-linked hypophosphatemia in childhood. It may occur in adults with severe bone deformations.