A Quality of Life Issue
The cardinal symptoms of vestibular schwannoma are unilateral hearing loss, tinnitus, vertigo, and unsteadiness. Most patients present with unilateral hearing loss (94%) and tinnitus (83%). Vestibular symptoms such as spinning vertigo, nausea, disequilibrium and imbalance have often been reported as mild, but are nevertheless present in 40 to 75% of patients. There is however remarkable variability in vertigo symptom severity and impact among patients. Several factors could explain this variability including the size of the tumour, the rate of growth, the rate of vestibular loss and the patients’ overall premorbid functioning level.
Recent studies focusing on quality of life associated with vestibular schwannoma have shown that when present, vertigo is the most debilitating and distressing symptom with respect to health-related quality of life. It also constitutes a risk factor for future work disability. While the subjective extent of impairment by vertigo is quite low initially, it could change considerably after intervention (surgery or radiation).
Why is there vertigo?
As humans, we orient ourselves in space with the input of our senses (vision, proprioception and vestibular function) integrated at the level of our central nervous system. The differential diagnosis of dizziness is therefore very broad.
The general complaint of «dizziness» is divided into four subtypes with different underlying etiologies: vertigo, disequilibrium, presyncope and psychological dizziness. Vertigo is a false sensation of movement of oneself or the environment. Disequilibrium is a sense of postural imbalance associated with a loss of balance that can relate to issues with the musculoskeletal system and proprioception. Presyncope is a feeling of faintness while psychological dizziness is typically related to anxiety or mood disorders. Vertigo can originate from a peripheral or central unilateral, asymmetric impairment of the vestibular system that causes an illusory sensation of movement.
The peripheral vestibular apparatus includes three semicircular canals, the utricle, saccule and the vestibular nerves. The central vestibular system comprises the vestibular nuclei, the brainstem, spinal cord, vestibular cortex and the cerebellum.
The role of the vestibular system is to help us maintain stable vision when the head is moving (through the vestibulocular reflex (VOR)) and to contribute to maintaining posture (through the vestibulospinal (VSR) and vestibulocolic reflexes (VCR)).
In the context of vestibular schwannoma, the tumour growth on one of the vestibular nerves affects the function of that nerve thus generating the asymmetry. It means that the vestibular reflexes (VOR, VSR and VCR) are impaired. Although acute changes of vestibular function can occur with vestibular schwannoma thus generating vertigo attacks with nausea, vomiting, lateropulsion to the lesioned side, and nystagmus to the contralesional side, the clear majority evolve so slowly that the changes of vestibular function are very subtle, and most patients do not experience severe a acks of vertigo. Vertigo is the presenting symptoms of only 10-15% of all vestibular schwannoma. More commonly, the patients with vestibular schwannoma might report symptoms of blurry vision for a split second when moving their head quickly toward the side of the lesion which is a sign of impaired VOR. They can also report a vague sense of imbalance and dizziness. Reports suggest that up to 75% of patients with vestibular schwannoma have some degree of vestibular symptoms.
As the tumor grows, it can put pressure on the brainstem and cerebellum thus generating more significant symptoms of dizziness and balance problems.
How does the approach to the management of vestibular schwannoma impact on vertigo?
The three commonly accepted treatment modalities for vestibular schwannoma include radiation therapy, microsurgery, and observation. Most studies comparing the different treatment approaches focus on comparing neurologic morbidity, hearing preservation and facial nerve function outcomes, all of which can be objectively assessed. Given that vertigo and dizziness are very subjective symptoms, the impact of treatment modalities on vertigo control is much more di cult to assess. A variety of scales and questionnaires have been designed to assess the extent and impact of vertigo (Dizziness Handicap Inventory (DHI, Vertigo Symptoms Scale (VSS), Short Form 36 Survey, Glasgow Benefit Inventory, etc.). None of these assessment tools is perfect as they all have their advantages and limitations. At the present time, while there is significant heterogeneity among small studies, there are no large-scale studies assessing vertigo symptoms systematically. It is therefore difficult to draw firm conclusions as to the impact of various treatment modalities on vertigo symptoms.
Smaller quality-of-life studies seem to suggest that surgery is associated with an increase in impairment of QOL by vertigo in the post-operative period. One study has shown that 31% of patients have disequilibrium lasting > 3 months after surgical removal of an acoustic neuroma. Worse outcomes were associated with age > 55.5 years, female gender, constant preoperative disequilibrium present for > 3.5 months, and central findings on electronystagmography.
Depending on the surgical approach, post-operative dizziness could be related to the extent of cerebellar retraction (retrosigmoid approach), and the loss of any residual vestibular function spared by the schwannoma. Because this change happens acutely at the time of surgery, vertigo is more readily perceived by the patient. Pre-operative vestibular function does impact the perceived dizziness after surgery. Therefore, someone who has had a slowly growing acoustic neuroma on one vestibular nerve and then has undergone surgical removal of the neuroma may exhibit almost no vestibular symptoms because the progressive and complete vestibular loss has already been compensated for progressively as the neuroma grew. By the time the surgery takes place, the patient has no effective vestibular function in the affected ear and the surgery could not worsen it further.
Because there is heterogeneity in the extent of vestibular function pre-operatively, there is a lot of variability among patients’ postoperative dizziness symptoms. Conversely, radiation therapy seems to be associated with lower rates of vestibular symptoms in the acute post-treatment period. Given that the impact of radiation can be felt for years after the treatment, some studies suggest an increase in dizziness in the years after treatment.
Treatment of Vertigo: What is vestibular physiotherapy and how does it work?
Regardless of the treatment approach to vestibular schwannoma, significant vertigo symptoms can be present and impact the patients’ quality of life. Specifically targeting these vertigo symptoms and overall balance is an important component of the care provided to patients with vestibular schwannoma. Given that regaining vestibular function on the tumor side is not possible, the therapeutic approach focuses mainly on optimizing compensation for this unilateral vestibular loss through vestibular physiotherapy.
Both animal and human studies emphasize the importance of early ambulation with head and neck mobilization in the first four post-operative days. Mobilization in this crucial period of recovery has a significant impact on the course of vestibular compensation. Encouragement and reassurance are needed at that time since patients might feel quite dizzy during this acute post-operative period and be very reluctant to move. Antiemetics and vestibular suppressants can be used to control nausea in this acute setting but should not be used long-term as they hinder the compensation process.
Vestibular compensation encompasses a variety of centrally mediated mechanisms that help us achieve vision and postural control despite the lack of vestibular input. At the level of the brainstem and cerebellum, the activity of the vestibular nuclei is modulated but the impact on maintaining the vestibular re exes is marginal. Compensation happens mainly through input substitution and learned anticipatory adjustments which can be trained.
The loss of vestibular function from one ear leads to increased reliance on vision and somatosensory information to perceive self-motion, orient the body, stabilize the head and control the center of mass. For instance, instead of the VOR, vision is stabilized though anticipated covert eye movements (saccades) that happen during the head movement.
Through a variety of exercises centered on stabilizing vision and maintaining balance while the head is moving, and the body is in motion, vestibular physiotherapy triggers the development of these alternative compensatory mechanisms. In the initial postoperative period, these exercises can feel as if they trigger the vertiginous symptoms because they bring out the vestibular deficit. This is the stimulus necessary for the brain to engage the compensatory mechanisms. With time and effort, desensitization to the symptoms and compensation occur while a more robust balance is achieved, all contributing to decreased vertigo and disequilibrium.
Tamara Mijovic MD CM FRCSC is an assistant professor of Otolaryngology-Head and Neck Surgery at McGill University.
As a fellowship trained Otologist and Neurotologist, she is the director of the McGill University Health Center (MUHC) Vestibular Laboratory and an active lateral skull base surgeon part of the multidisciplinary Skull Base Surgery Team at the Jewish General Hospital.