What Is Vestibulocerebellar Syndrome?
The vestibulocerebellar syndrome is also known as vestibulocerebellar ataxia. It is a hereditary condition primarily affecting the eyes, ears, and posture. It causes symptoms like abnormal eye movements, poor sense of sound, vertigo, etc. So far, only three families in the world have been affected by this condition and have had multiple generations afflicted by this condition, which characterizes the condition as autosomally dominant.
What Causes Vestibulocerebellar Syndrome?
Abnormalities in the genes responsible for the development of the central nervous system, specifically the ones creating and maintaining the flocculonodular lobe present in the cerebellum of the brain, are considered the potential cause for the development of this syndrome.
Researchers have not found any anatomical deformities that may cause abnormal eye movements in the affected individuals, which concludes that the resultant symptoms are due to failure in the floccular function.
What Is Cerebellum?
The cerebellum, also known as the little brain, is located at the back of the brain. It is primarily responsible for the following:
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Maintaining Posture and Balance - The cerebellum does not contain the neurons responsible for initiating motor commands. However, it is responsible for coordination, movements, balancing, and motor skills.
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Coordination of Voluntary Movements - The cerebellum coordinates the timing and force of different muscle groups to produce fluid limb and other body movements.
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Motor Learning - The cerebellum is important in learning to adapt and fine-tune motor movements through a trial-and-error process, for example, learning to hit a baseball.
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Cognitive Functions - Although the exact mechanism is not understood, the cerebellum is believed to be involved in certain cognitive functions, such as language.
Based on the functions mentioned above, the cerebellum is divided into three parts:
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Cerebrocerebellum - It is involved in planning movements and motor learning, regulates muscle activation coordination, and is important for visually guided movements.
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Spinocerebellum - Also involved in regulating body movements by allowing for error correction.
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Vestibulocerebellum - It is the functional equivalent to the flocculonodular lobe (when the cerebellum is divided based on anatomy). It controls balance and ocular reflexes, mainly the fixation of a target.
It is the malformations in this vestibulocerebellum that leads to the vestibulocerebellar syndrome.
Who Are Affected by Vestibulocerebellar Syndrome?
It is a familial disorder discovered in several generations of three families first observed by T.W. Farmer and his research associates in 1963 in rural North Carolina, USA. Apart from these families, there has been no record of individuals affected by this condition.
Not everyone in the family suffered from the condition. To be considered affected, the individual had to exhibit at least one of the primary and secondary criteria of symptoms.
What Are the Symptoms of Vestibulocerebellar Syndrome?
Symptoms of vestibulocerebellar ataxia are similar to episodic ataxia, but unlike the latter, the former does not completely lose control of the arms and legs. The following are the symptoms of vestibulocerebellar ataxia:
1. Nystagmus - It is a condition in which the eyes make rapid, repetitive, and uncontrolled eye movements. Of the many different types of nystagmus, the following two are commonly seen in vestibulocerebellar ataxia and they are:
- Gaze-Paretic Nystagmus - The individual cannot hold the gaze for a sufficient time due to neuron integrator dysfunction.
- Rebound Nystagmus - It is a transient nystagmus that appears on returning to a straight-ahead gaze after a long eccentric look.
2. Strabismus - A disorder in which both eyes do not line up in the same direction. Also known as crossed eyes.
3. Oscillopsia - A condition in which the visual object appears to be moving. The visual disturbance could be mild to frequent, rapid jumping.
4. Diplopia - Also known as double vision, it is defined as seeing two images of a single object.
5. Absence of Smooth Pursuit - The eyes cannot follow a moving object.
6. Abnormal Vestibulo-Ocular Reflex - It is a condition where the normal reflex eye adjustment to stabilize gaze during head movement does not occur.
Along with the eye abnormalities, periodic attacks of vertigo (spinning of the surroundings), cerebellar hemorrhage, tinnitus (perception of sound when no corresponding external sound is present), and ataxia (lack of voluntary coordination of muscle movement) were also seen in patients with the vestibulocerebellar syndrome.
The age for onset of attacks varies from 23 to 42 years, and duration ranges from a few minutes to two months in different individuals. The attacks can happen daily and, at times, may not happen for years, with a higher frequency in the morning.
How Is Vestibulocerebellar Syndrome Diagnosed?
The molecular basis for vestibular ataxia has not been identified yet, although possible genes like SOX21, ZIC2, and TYRP2 are currently being researched to investigate their possibility of causing the condition. Because of the undetermined gene and locus, it is impossible to perform genetic testing in the symptomatic individuals. However, a thorough family history, neurologic examination, and tests like nystagmogram are helpful in diagnosing vestibulocerebellar syndrome.
Apart from these, a CT (computed tomography) scan is also helpful in diagnosing vestibular symptoms. Patients with vestibulocerebellar syndrome will have small and discrete hemorrhages in or around the vestibulocerebellum. These findings may not be apparent in the initial stages of the condition, but it is important to perform one before making the final diagnosis.
What Is the Treatment for Vestibulocerebellar Syndrome?
As of now, there is no known cure for vestibulocerebellar ataxia. However, avoiding movements that exacerbate the attack has shown to be helpful. For example, lying down with eyes closed during an ataxic attack stabilizes the head in a fixed position and removes the unstable sensory input responsible for vertigo.
Medication is also an effective option to manage the symptoms and duration of attacks in these patients; for example, Acetazolamide has effectively treated episodic vertigo. In contrast, Dramamine and other antihistamine drugs have been shown to reduce the number and severity of ataxic attacks. Patients with cerebellar hemorrhage must be treated surgically through surgical evacuation.
Conclusion
The vestibulocerebellar syndrome is a progressive genetic condition affecting eye movements and the individual's orientation perception. Affected individuals experience symptoms early on, and as time progresses, they may find it difficult to perform daily tasks due to progressive ataxia. Family history plays an important role in diagnosing the conditions, and treatment mostly focuses on relieving the symptoms.
