What are the two types of vestibular hypofunction, and what are the signs and symptoms of each?
Types of Vestibular Hypofunction
There are two main types of vestibular hypofunction: unilateral and bilateral.
Unilateral vestibular loss (UVL). UVL, also referred to as unilateral vestibular hypofunction, involves a deficit or reduced function in the peripheral vestibular system on one side. The peripheral vestibular system begins at the point where the nerve exits the brainstem and extends into the ear, making it a peripheral problem.
Unilateral vestibular hypofunction accounts for up to 40% of all cases of dizziness and is the second most common vestibular issue after BPPV (Benign Paroxysmal Positional Vertigo). The condition is often associated with a viral infection of the vestibular nerve, but it can also occur without a clear cause, especially with age-related changes. In recent times, there seems to be a higher prevalence of dizziness associated with Covid infections, possibly contributing to an increase in vestibular hypofunction cases due to viral infections like Covid affecting the vestibular nerve.
This condition is often confused with BPPV because, in the initial stages of hypofunction, patients may experience spontaneous nystagmus, nausea, and similar symptoms. However, it's essential to rule out BPPV, and if present along with hypofunction, treat BPPV first before addressing the hypofunction.
The most common cause of Unilateral Vestibular Loss (UVL) is vestibular neuritis, and in 55 to 100% of cases, it involves the superior vestibular nerve, which supplies the utricle and is responsible for horizontal movements (horizontal and anterior semicircular canals). In some cases, inferior vestibular nerve involvement can occur (3.7 to 15% of the time), supplying the posterior canal and the saccule, which are responsible for vertical movements or labyrinthitis.
Signs and Symptoms of UVL. The signs and symptoms of UVL include an initial onset of dizziness that can last for hours and gradually improve over time, usually within one to three days. The nystagmus in hypofunction can last up to three days, but it tends to be more spontaneous and not triggered by positional changes, distinguishing it from BPPV.
After the initial onset, patients often describe a feeling of being off-balance, lightheaded, heavy, or foggy. They may experience discomfort while walking, driving, or in busy environments because their eyes are trying to compensate for the vestibular deficit. These symptoms may overlap with positional dizziness but without positional nystagmus, which is the key difference.
Bilateral Hypofunction. Bilateral vestibular loss (BVL) or hypofunction refers to a loss or reduction of function in the peripheral vestibular system on both sides. This condition is commonly caused by ototoxicity and aging, but in most cases, the exact cause is unknown (idiopathic).
The drugs commonly used to treat vertigo often worsen the symptoms because vestibular suppressants reduce the response of the vestibular system, which would otherwise help improve overall symptoms. However, if both sides of the vestibular system are not functioning normally and they are further suppressed, the symptoms tend to worsen, and individuals may feel more off-balance. Vertigo affects approximately 1.8 million people worldwide, and 88% of people with high bilateral loss report falling within a previous five-year period.
Signs and Symptoms of BVL. Oscillopsia, the sensation that the world is bouncing up and down, is a primary complaint among these individuals. They are unable to stabilize their eyes, leading to a bouncing sensation when walking or driving, which can severely impact daily activities. Many times, the dizziness is not as strong, but the chronic imbalance is the most challenging aspect to manage. People with bilateral loss often experience a sensation of falling and have chronic imbalance and postural instability. It becomes difficult to alleviate these symptoms as the functioning vestibular system is absent. Dizziness can occur in the acute stages, and some individuals have dizziness that persists all the time, while others may experience it intermittently or not at all.
In cases of bilateral loss, it's crucial to consider the impact on a person's daily life, especially when dealing with chronic imbalance and postural instability, as these can significantly affect their quality of life. Treatment approaches may need to focus on improving compensatory mechanisms and addressing specific challenges associated with this condition.
This Ask the Expert is an edited excerpt from the course Vestibular Hypofunction by Tonya Fuller, MSPT