Deafness

Definition

Partial or total loss of hearing in one or both ears.

Types

Conductive
Sensorineural
Mixed
Deafness

Causes

1- Congenital
a- Genetic : Syndromal (part of syndrome as down s., Treacher Collin s. , achondroplasia) or
Non-syndromal (deafness is the only complain), either autosomal dominant, recessive or x-linked.
b- Non-genetic:
i- intrauterine infection
ii- maternal DM or hypertension
iii- ototoxic drugs during pregnancy
iv- perinatal anoxia, hyperbilirubinemia or birth trauma.


2- Acquired (postnatal):
Conductive:
a- external ear
b- tympanic membrane
c- middle ear

Sensorineural:

a- sensory : damage to the sensory cell of the inner ear due to:
Trauma (Head injury or surgical trauma)
Noise induced
Blast injury
Endolymphatic hydrops
Presbyacusis
Autoimmune disease
Ototoxic drugs
b- neural: damage to cochlear nerve or auditory centers in the brain due to:
Trauma
Infection
Tumours
Vascular
Multiple sclerosis


1- History
Age of presentation
Progression
Events during pregnancy
Birth trauma
Neonatal infections
Other ear symptoms
Loud noise exposure
Drug history
Past medical and surgical history
Family history

Approach

2- Examination:

Ear , nose and throat : thorough exam.

General examination :stigmata of congenital anomaly.
Examination of other systems : including CNS, Cranial nerves, CVS .

Investigations

Should be selected in logical manner
1- auditory tests: allow qualitative and quantitative hearing assessment. Could be subjective or objective. Include :
A-pure tone audiometry (PTA)
Adults and children above 4 years
Both air and bone conduction tested using pure tones applied using special headphone and the results represented graphically. The pure tones are of different frequencies (Hz) and intensities (dB). Normal persons can hear pure tones at 20-25 dB or less. Greater than this is considered as hearing impairment which could be mild, mild-moderate, moderate, sever or profound.
B- speech audiometry: phonetically balanced words presented to the patient at different intensities and the patient asked to repeat these words. Normally 100% of the words can be repeated at 40 dB and 50% at 25%. This is called speech discrimination score.


C- Tympanometry :graphical representation of the middle ear pressure and compliance. Could be:
1- normal called type A. in which there is a peak of 0.4-1.3 ml with ME pressure between -100 to +50 mmH2o.
2- type B: flat curve with no peak. Occurs in patient with otitis media with effusion or tympanic membrane perforation.
3- type C : the point of maximum compliance below -100 mmH2o ( negative ME pressure). Occur in Eustachian tube dysfunction.
4- hypercompliant : greatly increased peak more than 3.5 ml as in ossicular disconnection.

D- Electric response audiometry:

Hearing generates action potentials along the auditory nerve and central connections. These potentials can be picked up using special electrodes placed externally on the skull or through the tympanic membrane from the cochlea and represented graphically.
These tests allow estimation of hearing threshold and localizing of the site of the lesion, and are mainly useful in young children and mentally handicapped patients and can be done under local or general anesthesia.

2- Blood tests : full blood count, ESR, bleeding profile

3- Biochemistry: sugar, urea, ceatinine, electrolytes, thyroid hormones.
4- Serological : for syphilis. TORCH (toxoplasmosis, rubella, cytomegalovirus, herpes virus).
5- Autoimmune profile: rheumatoid factor, antinuclear factor.
6- Urine analysis
7- Radiological : skull, mastoids, and sinuses as indicated using plain, CTS, and MRI.

Treatment

1- treat the underlying cause
2- general measures:
a- avoid exposure to loud noise
b- vasodilators : as betahistine, Ca channel blockers, low molecular weight dextran.
c- steroids
3- hearing aids : provide help in most types of deafness whether conductive or sensorineural .
Hearing aids is an electronic, sound amplifying device. It consists of the following parts:
a- microphone: transduce sound or acoustic energy into electricity.
b- amplifier: increases the electrical signal.
c- receiver or ear phone (loud speaker): transduce the electrical signal back into acoustic energy.


Types of hearing aids

1- body worn HA : the device attached to the clothes and connected to the ear phone by flexible wire. It is big sized and conspicuous.
2- ear level HA : or called behind the ear HA. The most widely used in which the whole device fits behind the auricle. It is more comfortable and less conspicuous than body worn but its amplifying power is less.
Both body worn and ear level hearing aids are air conduction HA.
3- bone conduction HA : the transducer press against the mastoid bone. It is useful in patient with atresia of the external auditory canal or chronically discharging ear. In both cases air conduction HA can not be used.

4- cochlear implantation

One of the new advances in the management of hearing loss. It is indicated in patients with bilateral sever or profound hearing loss in whom a trial of at least 6 months period with a hearing aid show no benefit.
The device consists :
a- external part : consists of a microphone( picks up sound from environment) , speech processor( filters sound into channel according to the frequency) and a transmitter (coil which transmits the processed sound signals into the internal device by electromagnetic induction.
b- internal part : implanted surgically in the mastoid bone and consists of a receiver and stimulator which converts the signals into electrical impulses and send them into the cochlea(scala tympani)through electrodes.