Hearing and balance problems in multiple sclerosis

Hearing

The auditory part of the audio-vestibular system comprises the outer ear, which receives sound and transmits it to the middle ear. In the middle ear, or more precisely at the back of the eardrum, there are three ossicles, the ossicular chain: the malleus, incus and stapes. When a noise or sound hits the eardrum in the form of a sound wave, it vibrates and transmits this to the ossicular chain. The ossicles serve to amplify and transmit the sound to the cochlea.

The cochlea is filled with fluid and contains sensory hair cells. These cells convert the sound waves into electrical signals, which are then transmitted via the auditory nerve to the brain, where they are perceived as sounds. The cochlea therefore converts the mechanical movements into an electrical nerve signal, which the person processes as hearing.

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Balance

The vestibular part of the system comprises the structures in the inner ear that are responsible for balance and spatial orientation. These include the semicircular canals, which register movements of the head and body, and the vestibular organs, which register linear acceleration and gravity. This information is transmitted to the brain to maintain balance and enable spatial orientation.

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Auditory nerves

The nerves from the organ of hearing and the organ of balance unite to form the auditory nerve. This enters the brain stem and is switched there in cranial nerve nuclei. From there, the signal is sent to the cerebral cortex. As it is important for the sense of hearing and balance that the signals are transmitted quickly, the nerve cells are insulated with myelin all the way from the inner ear to the cerebral cortex. You can think of the myelin as an insulating layer around the nerve. The myelin sheath is the basis for the rapid transmission of electrical signals.

Hearing problems in multiple sclerosis

Around one in a hundred MS patients report hearing impairment. In most cases, hearing problems occur in the form of sudden hearing loss, also known as sensorineural hearing loss or sensorineural hearing loss. “Sensorineural” here means that the cause of the hearing loss lies in the cochlea or the auditory pathway. As the nerve pathway is insulated with myelin on the way from the ear to the cerebrum, it is occasionally attacked and de-insulated as part of multiple sclerosis. This often occurs in the area of the cranial nerve nuclei, the 'switching stations' in the brain stem. However, it can also happen in the temporal lobe. This is the area of the brain where the sense of hearing is processed. But not only hearing loss, tinnitus and a feeling of pressure in the ear can also result.

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Balance problems & dizziness in multiple sclerosis

Dizziness describes a feeling of disorientation, swaying, lightheadedness, or the sensation of movement even though no actual movement is occurring. It can include a variety of sensations, including spinning vertigo (the feeling that the environment or one's own body is spinning or dizzy), swaying vertigo (the feeling as if one is swaying or staggering) or unsteadiness when walking or standing.Around one in three patients complain of dizziness at times during the course of their illness. Causes of dizziness include

• Vestibular causes (disorders of the organ of balance (vestibular organ))
• Causes in the central nervous system (CNS)
• Non-vestibular causes (e.g. cardiovascular diseases, muscle weaknesses or visual disorders)

Vestibular causes are divided into centrally vs. peripherally caused dizziness.

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Peripheral vestibular vertigo

Peripheral vestibular vertigo, also known as peripheral vertigo, is a disorder of the sense of balance that originates in the vestibular organ of the inner ear.

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Central vestibular vertigo

Central vestibular vertigo is a form of vertigo caused by disorders in the central nervous system, particularly in the brain. This form of vertigo can also be triggered by multiple sclerosis:The nerve fibers from the auditory as well as balance nerves are so-called peripheral nerves until they enter the brain stem. Just like the nerve tracts in the CNS, these peripheral nerves are surrounded by a myelin sheath, although this myelin sheath differs from that in the CNS. In MS, it is mainly the central nerve pathways that are affected, i.e. the pathways that transmit information from the peripheral nerves to the cerebral cortex. If an MS lesion occurs in the area of the nerve pathway for the sense of balance, the patient experiences dizziness.

Dizziness can be a symptom of multiple sclerosis, but can also be caused by other conditions. As the causes of dizziness determine the treatment, it is important to document symptoms and discuss them with the person treating you in order to initiate subsequent examinations if necessary.

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Diagnostic methods for hearing and balance disorders: MRI and evoked potentials

There are several options available for examining the sense of hearing and balance. The clinical examination is very important. MRI diagnostics and so-called evoked potentials can help to better classify the disorders.

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MRI examination for multiple sclerosis

An MRI scan (magnetic resonance imaging) is an imaging technique used to create detailed images of the internal structures of the body. It allows doctors to obtain detailed images of organs, tissues and anatomical structures such as the brain, spine, joints, muscles and internal organs. MRI examinations are routinely performed on MS patients.

The multiple sclerosis foci show up in the MRI as so-called “white matter hyperintensities (WMH)”, i.e. signal-intensive regions in the white matter of the brain. White matter is the part of the brain where the nerve pathways are located. Recent studies indicate that these WMHs have also been found in the cochlea and the auditory nerve in MS patients, which may indicate the involvement of these structures in MS. MS is traditionally seen as a disease of the CNS, which is why the involvement of peripheral structures sounds surprising at first. The fact that peripheral nerves can also be affected by MS is a relatively new finding and requires further research. Ear problems could therefore be a rare but important early symptom of MS.

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Evoked potentials

Evoked potentials can be used to display brain waves and measure transmission via the nerves and nerve pathways. To do this, electrodes are placed on the patient's skin and acoustic signals are played. These acoustic signals are then converted into electrical signals in the inner ear, as described above. In a healthy state, these signals are transmitted at a certain speed. If there is damage on the path between the ear and the cerebral cortex, this electrical signal is delayed. This delay can then be detected in the examination. In the case of damage to the auditory pathway, it is possible to determine where exactly on the path from the auditory organ to the brain the transmission is disturbed. Evoked potentials are also used to measure other sensory pathways, such as the visual pathway. The word 'evoked' refers to the fact that a stimulus is generated during this examination, for example a sound, which is then transmitted through the sensory organs into electrical signals to the brain.

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Treatment of auditory tract symptoms

In principle, it is important to discuss any symptoms that occur with those treating the patient, to clarify the causes and to develop an optimal treatment on this basis.Glucocorticoids are often used to treat symptoms of the auditory pathway, which are also used in higher doses in relapse therapy. The treatment of auditory pathway symptoms is merely symptomatic, i.e. a symptom is treated rather than the underlying condition or disease itself. The symptoms often subside on their own or only occur during relapses. If those affected still have problems with hearing despite drug therapy, hearing aids can be used.