Hearing loss in one ear

A condition in which a person stops perceiving sounds in one of the ears is defined as hearing loss in one ear - unilateral, unilateral, or asymmetrical, with the opposite ear hearing normally. Hearing loss can be mild, moderate or severe (commonly referred to as hypoacusis - hearing loss), or profound or complete (with a threshold for perceived sounds greater than 90 dB), which is referred to as deafness.

Epidemiology

According to some estimates, globally, up to 10% of the population suffers from unilateral deafness or hearing loss, and each year in the United States alone, nearly 60,000 people suffer from partial or complete hearing loss in one ear. [1]

Causes of the hearing loss in one ear

Among the causes of this hearing impairment experts include:

• earwax buildup - presence of a wax plug;
• a foreign body lodged in the ear;
• otitis media (exudative, purulent, tuberculous, etc.) and labyrinthitis (inflammation of the inner ear); [2]
• infections such as influenza, epidparatitis, bacterial and cryptococcal meningitis, tick-borreliosis, syphilis, tuberculosis, shingles with herpes virus VZV ear lesions. Unilateral deafness in adults - hearing loss in one ear after coronavirus is one of the neurologic manifestations of COVID-19 (SARS-CoV-2) infection, which has been found to be able to impair the function of the cochlea of the inner ear. [3], [4], [5]

Asymmetrical hearing loss can be caused by:

• Eardrum perforation; [6]
• acute acoustic trauma, as well as inner ear barotrauma; [7]
• bone overgrowth in the inner ear - otosclerosish and sclerosis of the tympanic membrane (membrana tympani) - tympanosclerosis; [8]
• inflammation of the eustachian (auditory) tube - tubo-otitis (tubotympanitis), as well as its obstruction due to hypertrophy of the tubal tonsil; [9]
• Endolymphatic hydrocele or Meniere's disease; [10]
• disorders associated with benign masses such as cholesteatoma in the middle ear, [11] paraganglioma glomus tympanicum or glomus tympanicum middle ear tumor, [12] as well as vestibular schwannoma, acoustic neurinoma or auditory nerve neurinoma; [13]
• ototoxic effect of drugs leading to the development of degenerative labyrinthotoxicosis.

Due to a rupture of the middle ear ossicle chain in a traumatic brain injury, as well as in inner ear injuries with labyrinth trauma syndrome - in a severe concussion with damage to the ear labyrinth or its contusion in a temporal bone contusion - there can be an abrupt loss of hearing in one ear. It can also be caused by the formation of a perilymphatic or labyrinthine fistula (an abnormal connection between the middle and inner ear) in head trauma or the so-called sudden deafness syndrome. [14]

In addition, unilateral hearing loss can be congenital, and its etiology is most often related to an anomaly of the ear canal, hypoplasia or absence of the cochlear (auditory) nerve, and damage by cytomegalovirus infection.

Also read:

• Causes of hearing loss
• Causes of hearing loss

Risk factors

Recognized risk factors for asymmetric hearing loss are: middle ear disease of infectious nature - with fluid accumulation in the ear; common viral infections; trauma to the ear or head (including damage to the temporal bone, in the thickness of which the bony labyrinth of the inner ear is located); exposure to noise, as well as diabetes, vascular disorders (carotid atherosclerosis), increased intracranial pressure, multiple sclerosis, use of ototoxic drugs.

Pathogenesis

In cases of unilateral hearing loss of varying degrees, the pathogenesis is determined by the type of hearing loss: conductive hearing loss (associated with problems of the outer and middle ear and its structures), [15] sensorineural or neurosensory hearing loss (resulting from damage to the inner ear and its sound-receptive apparatus) [16] or mixed (combining conductive and neurosensory disorders).

Thus, the mechanism of hearing loss due to middle ear inflammation is caused by the formation of scar tissue, which negatively affects the auditory ossicles, limiting their mobility. In otosclerosis, the function of the auditory ossicles is also impaired, leading to their stiffness; in cases of sclerosis of the tympanic membrane separating the middle and inner ear (whose vibrations should actuate the auditory ossicles), its thickening and decreased elasticity have a negative impact on hearing. [17]

Labyrinth damage in infectious diseases explains unilateral hearing loss after viral and bacterial infections, such as the development of influenza labyrinthitis after influenza.

More information in the material - Peripheral vascular destructive labyrinthine syndrome

Unilateral sensorineural hearing loss is the result of atrophy, degeneration and dysfunction of the sensory-epithelial hair cells of the receptor section of the auditory analyzer (organ of Cortium) of the inner ear, which convert perceived sound vibrations into electrical impulses.

And at the neurinoma of the auditory nerve are affected schwann cells of the myelin sheath of the VIII pair of cranial nerves, which transmit nerve impulses to the auditory zones of the temporal lobes of the cerebral cortex.

Symptoms of the hearing loss in one ear

The first signs of unilateral hearing loss may be ear stuffiness and difficulty hearing soft sounds - in cases of mild hearing loss. In more severe cases, it may be difficult to hear sounds of normal volume in the affected ear. Severe hearing loss occurs when one ear can barely hear sounds.

There are usually associated symptoms such as pressure in the ear, constant tinnitus and ringing in the ears of varying intensity.

In inflammatory processes as well as rupture of the eardrum, patients have ear pain and hearing loss.

When sudden hearing loss occurs, dizziness is common (indicating problems with the inner ear).

There may be hearing loss in the right ear (e.g. Left-sided paralysis after a stroke), defined as right-sided hearing loss or deafness. There may be left-sided hearing loss or deafness - hearing loss in the left ear - for a variety of reasons.

Asymmetric or unilateral deafness is defined as complete hearing loss in one ear, while partial loss is diagnosed as unilateral hearing loss

Complications and consequences

Hearing loss is a progressive pathological process, and its complications and consequences include a gradual increase in the frequency of perceived sounds - up to complete deafness.

Diagnostics of the hearing loss in one ear

To detect hearing loss, a hearing test and an otoscopic examination of the ear.

Instrumental diagnostics are used: tone audiometry, [18] acoustic impedanceometry - tympanometry, [19] otoacoustic emission, [20] electrocochleography, [21] X-ray or CT scan of the temporal bone, MRI of the head.

Differential diagnosis is aimed at determining the cause of hearing loss.

Treatment of the hearing loss in one ear

Treatment for unilateral hearing loss depends on the cause: it is easiest to remove a wax plug or a foreign body trapped in the ear.

Medication and physiotherapeutic treatment of otitis media and tubo-otitis is mandatory; there is treatment of Meniere's disease etc. [22]

Surgical treatment includes:

• removal of cholesteatoma and glomus tumor of the middle ear;
• hearing aid prosthetics - ossiculoplasty; [23]
• restoration of the integrity of the damaged tympanic membrane - tympanoplasty; [24]
• stapedotomy [25] and stapedoplasty [26] (middle ear stapes operations in cases of otosclerosis).

Neurosurgical surgery to remove an auditory neuroma may also be performed, [27] but in most cases of sensorineural hearing loss, hearing aids are needed. [28] For more information, see Treatment of sensorineural hearing loss.

Prevention

To prevent the development of hearing loss in one ear, it is necessary to treat its inflammation, keep water out of it, avoid loud noises and the use of drugs with toxic side effects on the ears.

Disability for hearing loss refers to a hearing loss of more than 35 dB in the better hearing ear. In Ukraine, children up to 16 years of age are eligible for state social assistance for mixed and sensorineural unilateral hearing loss (in the speech frequency zone of more than 90 dB) - with normal hearing in the opposite ear.

Forecast

The prognosis for hearing loss in one ear is influenced by many factors, most notably its cause and the degree of impairment of the auditory system, as many hearing impairments are irreversible.