The ear and balance
The inner ear contains the sensory organs for hearing - the cochlea, and balance - the vestibular system (see picture).
These organs consist of fluid-filled chambers containing cells that can detect movement. In the cochlea, sound waves passing through the fluids are detected by hair cells and converted into electrical signals which are sent to the brain and perceived as sound. In the vestibular system, the speed and direction of movement of the fluid is detected by a different type of sensory cell, which sends balance signals to the brain.
Your brain uses the combined information from the vestibular system of each ear to understand the position of your head in three-dimensional space; and the direction and speed of movement of your body. This information is then used to control movements of the eye and the skeletal muscles so that adjustments can be made to keep the body balanced and orientated.
These interacting brain signals occur very rapidly and, when the vestibular system is working properly, muscle adjustments are made continuously without us even thinking about it. But, when the vestibular system is not working properly, these brain signals go out of sync, leading to symptoms such as dizziness and loss of balance.
What is Ménière’s disease?
Ménière’s disease is a condition of the inner ear that causes vertigo (severe dizziness), tinnitus, a feeling of fullness or congestion in the ear, and hearing loss. The symptoms, caused by the build-up of fluid in the compartments of the inner ear, usually only affect one ear.
The most dramatic effect of this fluid build-up is that it alters the signals from the vestibular system. As a result, the brain receives conflicting information from the affected and unaffected ear. This means it can’t determine the position of the head in space, leading to vertigo and loss of balance. Signals from the cochlea can also be altered, resulting in tinnitus and, in some cases, fluctuating hearing loss.
Causes and treatments
Research into the reasons behind the fluid build-up in Ménière’s disease is ongoing, but we don’t yet know the exact cause. There is some evidence that it could be due to changes in blood flow to the inner ear – or a consequence of viral infections, allergies, or autoimmune reactions. 7-10% of affected people have a family history of the condition so there may also be a genetic component. Ménière’s disease can develop at any age, but it is more likely to occur in adults aged between 40 and 60.
There is no cure for Ménière’s disease, but there are ways to relieve and manage the symptoms. GPs may recommend reducing salt intake or prescribe a diuretic to reduce the fluid levels in your inner ear and salt levels in your body. Steroids can help – especially if your symptoms include a sudden decrease in hearing. In severe cases that do not respond to treatment, surgery may be required.
A new steroid therapy?
Steroids are thought to help treat the symptoms of Ménière’s disease by reducing inflammation caused by viral infections or allergic reactions. They may also play a role in regulating the levels of sodium and potassium in the fluids of the inner ear. Steroids can be given orally, but this can have unwanted side effects, especially if high doses are needed. To avoid these side effects, steroids can be given by injection through the eardrum directly into the middle ear. The disadvantage of this approach is that much of the steroid dose can be lost from the middle ear through the Eustachian tube and swallowed before it has a chance to diffuse into the inner ear.
A new experimental medicine, OTO-104, aims to address this problem and is currently being tested in clinical trials, both here and in the USA. OTO-104 is a long-acting gel containing the steroid dexamethasone, which is injected through the eardrum into the middle ear where it slowly releases the steroid. In a previous clinical trial in the USA with a small group of Ménière’s disease patients, a single dose of OTO-104 was shown to be safe and well-tolerated – and appeared to reduce vertigo frequency, and improve the patients’ tinnitus symptoms.
Now, a larger clinical study is investigating the safety of multiple doses of OTO-104, and its effectiveness compared to placebo (dummy) treatment in reducing the frequency of extreme vertigo. The UK part of the study is being conducted at several hospitals across the country: 125 people with Meniere's disease are needed to take part, for around 12 months.
Rigorous clinical trials like these are essential to test whether an experimental medicine is safe and effective. If a new medicine successfully completes all the phases of clinical testing, health regulators, doctors, and the public can be confident that it is safe and proven to help the people who need it.