Introduction
Vertigo and dizziness are common complaints of patients at all ages with a lifetime prevalence of around 15–35% in the general population [
1]. They are a multisensory and sensorimotor syndrome with perceptual, postural, ocular motor and autonomic manifestations that is usually caused by a mismatch of information between vestibular, visual, and somatosensory systems. The relevant structures of the vestibular system run bilaterally from the inner ear, via the vestibular nerve, brainstem and cerebellum upward to temporo-parietal multisensory cortical network areas.
In addition to marked functional impairment, vertigo and dizziness significantly impact psychological health [
2]. The various vertigo syndromes differed significantly in terms of psychological distress in the acute phase and even more so at repeated follow-up examinations over a year [
3‐
6], irrespective of vestibular function [
7]. The assessment of a manifest psychiatric comorbidity revealed a significantly higher prevalence in patients presenting to specialised vertigo centres (40–60%), than that expressed in the general population (20–30%) [
3,
6,
8]. Again, large differences were seen between different vestibular syndromes, e.g. manifest anxiety disorders were found in almost 50% of patients with vestibular migraine (VM), but in only in 24% with bilateral loss of peripheral vestibular function (bilateral vestibulopathy; BVP) [
3‐
6].
While general anxiety disorders are highly individual and complex in genesis [
9], in the past the question arose of how the symptom of vertigo and dizziness itself affects symptom-specific anxiety, independent of a manifest psychiatric disorder. This includes vertigo-related phobic avoidance, anxious beliefs and also social anxiety. For this purpose, various questionnaires have already been evaluated in previous studies [
10], whereby the Vertigo Handicap Questionnaire (VHQ) with its subgroups for anxiety and activity-related impairment appeared to be a promising tool [
11]. A study by Decker and colleagues assessing vertigo-related anxiety (VRA) in 7083 patients with the key symptoms of vertigo or dizziness by using the VHQ subscales found significantly lower scores in BVP patients despite their well-known high activity impairment and increased risk of falling compared to patients with preserved peripheral-vestibular function, e.g., VM or functional dizziness [
12‐
14]. From this, the current hypothesis was derived that an intact peripheral vestibular system is a prerequisite for the development of VRA thereby substantiating the close linkage between the vestibular and anxiety systems [
15].
There are several studies demonstrating the structural and functional relationships between the vestibular system and emotional, cognitive and visceral functions in humans and other animals [
16‐
20] comprising reciprocal connections of thalamocortical and limbic pathways [
16,
20], connections with the cerebellum [
20,
21] as well as noradrenergic and serotonergic projections [
21,
22]. In a recent MRI meta-analysis, the areas of overlap between the vestibular system and the anxiety system were demonstrated in the upper brainstem and cortex [
23].
While the influence of bilateral peripheral vestibular hypofunction on anxiety and especially on VRA is just starting to be understood, the influence of persistent central vestibular disorders on emotional processing is still largely unknown. A study on psychiatric comorbidity among patients with vestibular disorders reported generally increased comorbidity rates in “central vertigo” by about 42.1%, but the prevalence of anxiety disorders was comparably low to that of BVP (18.4% vs.17.8%) [
6]. However, the number of patients with “central vertigo” enrolled was relatively small, and their aetiology too heterogeneous to allow more precise statements. The aim of the current study therefore was to specifically evaluate vertigo and dizziness related anxiety and handicapped activity in different types of central vestibular disorders.
Discussion
The main findings of our study on subjective vertigo-related physical and psychological impairment based on the Vertigo Handicap Questionnaire (VHQ) in relation to objective stance function measured by posturography in different types of central vestibular dysfunction were as follows:
1.
The VHQ, which assesses impairment in daily life due to vertigo or dizziness, was generally increased in central vestibular disorders, even if compared to peripheral vestibular disorders, but showed marked differences depending on the distinct diagnoses.
2.
Patients with VM showed the lowest vestibular-related activity impairment. Patients with COD and BVP reported similarly low levels, although BVP patients suffer from relevant postural deficits. As expected, CA and APS reported significantly higher handicapped activity compared to BVP and VM.
3.
Patients with chronic central vestibular disorders reported vertigo-related anxiety, VRA, at comparably low levels as BVP patients. Only patients with VM showed significantly higher anxiety scores compared to the other central vestibular disorders.
4.
The multivariate linear regression analyses revealed an overall effect of age, sex and peripheral sensory impairment (polyneuropathy) on VRA. The subgroup analyses revealed that polyneuropathy increased the anxiety in BVP and COD, but not in the other groups. VM was the only subgroup with a positive correlation between anxiety and ageing. Gender had no effect on VRA in the subgroup analyses.
5.
Postural instability increased with higher demands of the stance conditions. Patient subgroups differed in their postural instability, and CA showed consistently higher instability than other patient groups, whereas VM showed consistently low sway variability over all conditions.
6.
Objective sway variability correlated with subjective activity impairment but did not correlate with subjective anxiety, VRA. This was especially true for VM, who showed the lowest sway variability and activity impairment, but the highest anxiety scores.
The starting point of our study was the previous finding that patients with a loss of peripheral vestibular function, such as unilateral (UVP) or bilateral vestibulopathy (BVP) show relatively low anxiety levels compared to other vestibular disorders in a specialised vertigo centre [
12]. This led to the hypothesis that an intact peripheral vestibular system is a prerequisite for the development of VRA [
15]. While UVP is a monophasic event that rarely causes ongoing disabilities after complete central compensation [
38], BVP leads to a persistent vestibular and postural impairment associated with an increased risk of recurrent and injurious falls [
13]. Surprisingly, the latter patients have only low to moderate fear of falls [
13]. Accordingly, BVP patients do not have an increased susceptibility to fear of heights, indicating a generally lowered perception of vestibular related anxiety in patients with BVP [
39].
Numerous connections at lower and higher brain levels exist between the vestibular and emotional systems, including various central areas concerned with anxiety perception, e.g., projections to the parabrachial nucleus and its reciprocal connections with amygdala, infralimbic and insular cortex, and hypothalamus [
16,
20,
40]. These connections indicate a close structural and functional connection between vestibular input and emotional processing, which is reflected in the rates of vestibular and affective comorbidities [
6]. However, the complex interplay between these two systems, in particular the role of central vestibular impairment in the development of VRA remains largely unknown.
In our study patients with chronic central vestibular disorders surprisingly reported comparably low levels of anxiety as patients with BVP and without significant differences within these patient groups. Even patients with CA, who demonstrated the highest subjective activity impairment and stance instability in posturography, showed relatively low VRA. Overall, postural instability correlated with self-reported activity impairment across all diagnoses, but not with VRA. This suggests that, in line with previous studies [
41,
42], VRA is not related to an objective physical impairment of stance and gait regulation. Rather, the proper function of the central as well as the peripheral vestibular system is relevant for the development of vertigo-related anxiety.
Compared to earlier data, it is important to note that Lahmann and co-workers reported manifest psychiatric comorbidity in dizzy patients [
6], whereas we evaluated specific vertigo-related anxiety in patients with vestibular disorders that do not fulfil the criteria for an associated psychiatric disorder. However, the results of the two studies fit nicely together, since manifest anxiety disorders were even rare comorbidities in their inhomogeneous group of central vertigo (18.4%) and BVP patients (17.8%) compared to the total patients’ average (28.9%) [
6].
Our study provides new insights into different subgroups of central vestibular disorders:
Increasing evidence indicates the cerebellum’s influential role in various higher cognitive and emotional processes, particularly for susceptibility to anxiety [
21,
43,
44]. In his internal model hypothesis, Hilber proposed that cerebellar or vestibular disorders induce an alteration of sensory information by altering the integration process of exteroceptive and proprioceptive information [
20]. This leads to false anticipation as well as motor and coordinative and subsequently also social interaction with the environment, resulting in stress and anxiety. In fact, Schlick and co-workers found an association between high levels of recurrent falls and high levels of specific fear of falling in cerebellar disorders [
13]. In contrast, in our study we did not find a relationship between the VRA and postural instability in patients with cerebellar disorders, not even in the considerably more activity-handicapped subgroup of CA.
Already at an early stage neurodegenerative disorders are often associated with balance disorders and spatial disorientation, assumed to result from a disturbed central processing of multisensory information with involvement of the vestibular, visual, somatosensory and motor systems [
45]. An autopsy-confirmed case series found that dizziness was indeed the first clinical symptom in 4.2 to 7.7% of the subgroup of patients with atypical Parkinson's syndromes (APS) [
46], who develop high postural instability with increased risk of falls during the course of the disease [
13]. In our study, however, VRA levels in APS were similar to those in BVP, although the subjective handicapped activity and objective postural instability of these patients were high. This further points towards a more complex interplay between vestibular function and the development of specific VRA.
VM patients stood out from the other central vestibular disorders showing an inverse pattern of high VRA despite low subjective handicapped activity and good postural performance. This is consistent with a prospective one-year follow-up study that reported ongoing high psychological distress with significantly elevated “vertigo-induced anxiety” levels in VM [
5]. A systematic review confirmed an overall strong and continuing positive relationship between migraine and anxiety [
47]. Potential pathophysiological mechanisms include altered signalling mechanisms in the brainstem and thalamus as well as trigeminovascular activation [
47] and disturbances in intracerebral GABAergic inhibition as in panic disorders [
5]. Notably, VM is the only central vestibular disorder of episodic type addressed in our study with vertigo attacks that typically do not cause significant vestibular deficits in the interictal interval. The acute and unpredictable occurrence of VM attacks could be a trigger for enhanced VRA [
3].
The majority of our patients, with the exception of VM patients, were above 60 years of age. Age is a relevant factor for dizziness and balance disorders due to increasing comorbidity [
48]. No overall impact of age, sex or sensory impairment (polyneuropathy) was found on vertigo-related handicap and activity impairment. However, a significantly increased VRA was evident in the presence of polyneuropathy in BVP and COD. It is well-known that proprioceptive and visual feedback is of particular relevance for BVP, which is reflected by posturography under visual and sensory perturbation [
14]. Notably, only the subgroup of VM showed an increase of VRA with higher age, although the incidence of VM typically decreases with advanced age and persistent relevant vestibular or ocular motor dysfunction in the attack-free interval is rare [
49,
50]. This further points towards the special entity of VM and its interplay with the anxiety system.
In summary, subjective and objective vestibular-related impairment is not necessarily correlated with vestibular-related anxiety in central vestibular disorders. Rather, our findings support the view, that in addition to an intact peripheral system, also an intact central vestibular system might also serve as a prerequisite for the development specific VRA.
The main limitation of our study was its retrospective approach with a potential selection bias due to referral to a tertiary vertigo centre. Consequently, patients included might be more severely burdened, and the data cannot be easily transferred to the general population. Retrospectively, we were not able to perform a wider range of standardised psychiatric questionnaires, but a careful evaluation of current complaints and patient history including psychiatric comorbidities was routinely performed during the presentation. Further studies are needed to investigate the complex interplay between the vestibular system, anxiety, vestibular-related anxiety, and psychiatric comorbidities as well as their influences on daily living and quality of life in more detail.