Diagnostic criteria for persistent postural-perceptual dizziness (PPPD): Consensus document of the committee for the Classification of Vestibular Disorders of the Bárány Society

4.1.1 Core vestibular symptoms

The primary symptoms of PPPD are dizziness, unsteadiness, and certain types of non-spinning vertigo [13, 75]. The dizziness of PPPD is a non-motion symptom [9] that patients may describe variously as cloudiness, fuzziness, fullness, heaviness, or lightness in the head, or a feeling that their spatial orientation is not sharp or visual focus is not clear. Unsteadiness is a sensation of instability or wobbling when upright, or a feeling of veering from side to side when walking without a directional preponderance [9]. Non-spinning vertigo encompasses feelings of swaying, rocking, bouncing, or bobbing that patients may describe as motion inside their heads, involving their entire heads or bodies, or occurring in the environment. Tilting and sliding sensations are included in the Bárány Society’s definition of non-spinning vertigo [9], but these are not typical symptoms of PPPD [12, 75]. Intermittent, momentary sensations of illusory movement that last no more than a few seconds (Note 3) may include both spinning and non-spinning vertigo [12, 13].

4.1.2 Temporal pattern of symptoms

PPV was defined by fluctuating postural symptoms and momentary illusions of movement [12, 13]. SMD was described as a situational phenomenon, occurring during exposures to provocative stimuli [39, 43]. The earliest reports of VV [15] also focused on situational symptoms, though recent investigations identified a link between persistent VV and chronic dizziness [22, 23]. Definitions of CSD [75, 79] emphasized chronic symptoms lasting throughout the day and exacerbated by motion stimuli. One study found that symptoms of CSD were absent or mildest for about an hour after patients awoke in the morning, but then increased as the day progressed [27]. These observations identified the two temporal patterns incorporated into PPPD. Patients experience a background of vestibular symptoms throughout the day, nearly every day [13, 75]. Symptom-free intervals tend to be brief (minutes to hours), though a distinct minority of patients may experience symptom-free periods lasting for days to weeks. Symptoms wax and wane spontaneously, but are aggravated by the three exacerbating factors of Criterion B. When free of these circumstances, patients’ symptoms may be innocuous, limited to non-motion dizziness with minimal unsteadiness or non-spinning vertigo. However, all symptoms are susceptible to exacerbation with upright posture, motion, and exposure to complex visual stimuli. On exposure to these situations, sensations of unsteadiness and non-spinning vertigo tend to dominate the clinical picture.

4.1.3 Exacerbating factors

The exacerbating factors included in Criterion B were described in all or most of the precursors of PPPD (Table 1). Upright posture, active or passive movement, and exposure to visually complex or moving stimuli aggravate the core symptoms of PPPD. There are no data to identify one of these factors as being consistently more troublesome than the others or to determine the sensitivities and specificities of requiring the presence of one, two, or all three factors to make a diagnosis of PPPD. Therefore, the consensus definition of Criterion B requires that affected individuals report at least some difficulty with all three factors, while recognizing that patients will not be equally sensitive to all of them, and that the most troublesome of these factors will vary from one patient with PPPD to another.

Symptoms may not increase immediately on standing, moving, or entering visually stimulating environments. Rather, they tend to build throughout continued exposure. Symptoms usually do not return to baseline immediately on cessation of exposures, but may last for hours or more thereafter. This pattern differs from that experienced by patients with structural vestibular deficits whose symptoms increase and decrease in close temporal relationship to motion. Patients with PPPD may express concerns about having to endure increases in their noxious symptoms on exposure to exacerbating factors, but this differs from individuals with anxiety disorders who focus more on fears of becoming incapacitated, injuring themselves or others, or attracting unwanted attention when exposed to situations that they fear.

4.1.3.1 Upright posture. Most patients with PPPD report more severe symptoms when standing or walking than when sitting or lying down [12, 75]. Individuals who are particularly sensitive to postural changes may experience increased symptoms when sitting upright or leaning backward in a seat without back or arm support. Patients may not have a complete resolution of symptoms when lying down, but recumbent postures are the least troublesome. Patients may minimize the adverse effects of upright posture by touching fixed objects, using gait aids, or holding onto other people. Patients do not have to hold tightly to support their weight. Rather, a light touch is sufficient to obtain the stabilizing effect of somatosensory input.

4.1.3.2 Active or passive movement. Movements that exacerbate symptoms may occur in any direction or position. Most patients find that active and passive motions are troublesome in direct proportion to their intensity. Speed, duration, and repetition of movement appear to be more important than whether motion is actively or passively induced. High velocity movements that are prolonged or repeated are universally provocative whether encountered actively or passively. Responses to less intense movements vary among affected individuals. Most patients feel best when still, but others report that moving at a modest pace (e.g., walking or riding a bicycle) is more tolerable than remaining stationary when upright [24].

4.1.3.3 Visual stimuli. Visual stimuli that exacerbate symptoms may be moving or stationary. Environments that contain full field visual flow (e.g., passing traffic especially at high speed on a highway or motorway, large crowds of people milling about), large complex patterns (e.g., an expanse of busy carpeting, large store displays), or wide-open spaces with distant or indistinct visuospatial reference points (e.g., large fields, warehouses, atria) are most troublesome [15, 75]. Exposure to full field visual stimuli may exacerbate symptoms for hours, even after brief exposures. Smaller visual targets (e.g., books, mobile electronic devices) may be troublesome when held at a close distance. Performing tasks that require precision visual focus (e.g., using a computer, or watching television) may exacerbate symptoms even when patients are sitting still [75, 81]. The increasing need to view information on electronic screens in the modern world is a bane for many patients with PPPD.

4.1.4 Clinical course

In most cases, PPPD develops as the acute symptoms of precipitating conditions remit [24]. Patients do not experience symptom-free intervals. Instead, as their acute vertiginous symptoms fade, they develop the characteristic chronic symptoms of PPPD. In other cases, PPPD has a stuttering onset in which patients may experience PPPD-like symptoms lasting days to weeks, until recurrences settle into a persistent course. This stuttering course is more likely when precipitants are short-lived, recurrent events (e.g., attacks of BPPV, migraine, or panic). Least often, PPPD has a gradual onset. Precipitants such as generalized anxiety, autonomic disorders, and degenerative diseases of the peripheral vestibular apparatus or cerebellum are chronic conditions that may develop slowly. With these precipitants, symptoms of PPPD may appear gradually, almost imperceptibly at first, and then worsen slowly.

Specific precipitants of PPPD cannot be identified in all patients, especially those who have been symptomatic for many years and lack adequate documentation of their initial clinical presentations or cannot recall the details of their earliest symptoms. Even in these situations, however, most patients describe an acute, subacute, or stuttering onset of illness. Patients with clinical histories of gradually worsening chronic vestibular symptoms or balance problems that have no identifiable starting points, particularly those without generalized anxiety or autonomic problems, are less likely to have PPPD than those with more definitive onsets of illness. They warrant prospective observation over a period of several months to verify the diagnostic picture and properly screen for other diseases, especially slowly emerging degenerative disorders.

4.2.1 A single disorder or a group of related conditions?

The precipitating factors of PPV [13], SMD [39], VV [15], and CSD [79] span a variety of neuro-otologic, other medical, and psychological conditions. It is not known if these act through one pathophysiologic process to produce a single syndrome or via separate mechanisms that share enough of a final common pathway to generate symptoms and susceptibilities to exacerbating factors that closely resemble one another. The former situation would be akin to posttraumatic stress disorder in which a wide variety of traumatic experiences precipitate one syndrome with four clusters of symptoms that can be exacerbated by internal and external factors [3, 95]. The latter circumstance would be like hypertension in which chronically elevated blood pressure can arise from multiple diseases that produce sustained increases in intravascular pressure via different physiologic mechanisms.

4.2.2 Do subtypes exist?

Although PPV, SMD, VV, and CSD share a number of features, they also have different areas of emphasis (Table 1). Postural provocation is a distinguishing feature of PPV [12, 13]. It was not part of the original description of CSD [81], but was added later [75]. Difficulty with self-motion is part of PPV [12, 13], SMD [39], and CSD [75, 81]. Trouble with visual motion stimuli is the primary feature of VV [15, 29, 63] and is emphasized in SMD [39, 43] and CSD [75, 81]. Thus, PPV, SMD, VV, and CSD may reflect different perspectives on a single, multifaceted clinical entity or they may offer insights into potentially distinguishable subtypes of PPPD (e.g., posturally predominant subtype, visually predominant subtype). Mild anxiety and depressive symptoms and phobic behaviors were included in the descriptions of PPV [12, 13], but were considered comorbidities of CSD [24, 80]. This raises the possibility that PPV may be either a distinct phobic subtype of PPPD or encompass PPPD plus a specific phobia of dizziness-related experiences.

In the absence of definitive scientific data on these possible subtypes, the Behavioral Subcommittee chose to define only PPPD for the ICVD, but allow for clinical variability as reflected in Criterion B. The World Health Organization permits related terms to be listed in the ICD-11. Therefore, PPV, SMD, VV, and CSD were retained as index terms for cross-referencing in the ICD-11 beta draft definition of PPPD [97].

4.2.3 Probable (subthreshold) PPPD

Members of the subcommittee concluded that there were not enough published data to define a clinically meaningful probable or subthreshold version of PPPD. Clinical experience with PPV and CSD suggests caution in applying the diagnosis of PPPD to patients who do not fulfill all five of its diagnostic criteria.

4.4.1 Chronic sequelae of acute precipitants

Some precipitants of PPPD are acute disorders that have the potential for chronic symptomatic complications (e.g., vestibular neuritis or stroke leading to persistent uncompensated vestibulopathies). For these disorders, the diagnostic question is whether patients’ presenting symptoms are due to PPPD alone, chronic manifestations of its precipitants, or both [24]. This diagnostic dilemma is resolved by careful attention to the clinical history and assessment of patients’ compensation status. A history of persistent non-vertiginous dizziness and unsteadiness provoked by upright posture, patients’ own movements, and exposure to visual motion stimuli plus physical exam and laboratory evidence of good compensation (e.g., no spontaneous nystagmus or abnormal responses to head thrust, headshake, or stepping tests) indicates that PPPD is the only active diagnosis. In contrast, the presence of ongoing episodes of head motion-provoked vertigo or unsteadiness without persistent dizziness and exam findings of incomplete compensation argues against PPPD. A third possibility is the combination of persistent dizziness and motion sensitivity plus head motion-provoked symptoms and exam findings of incomplete compensation, which would indicate coexisting PPPD and uncompensated vestibulopathy.

4.4.2 Recurrent attacks of episodic precipitants

PPPD may be preceded by episodic vestibular disorders such as vestibular migraine [49], Menière’s disease [51], and BPPV [87] that cause distinct bouts of vestibular symptoms in contrast to the persistent, waxing and waning dizziness, unsteadiness and non-spinning vertigo that are hallmarks of PPPD. When PPPD co-exists with these disorders, proper diagnosis rest on identifying the characteristic symptoms of each active disorder. Episodic disorders add distinctive vestibular symptoms to the background of PPPD [58], such acute attacks of vertigo plus cephalalgia, photophobia and phonophobia, with or without visual aura for vestibular migraine [49], short-lived positional vertigo for BPPV [87], or attacks of vertigo, tinnitus, and fluctuating hearing for Menière’s disease [51].

4.4.3 Ongoing manifestations of chronic precipitants

Some precipitants of PPPD are chronic conditions themselves (e.g., anxiety and depressive disorders, post-concussive syndrome, autonomic disorders, and heart diseases). They may cause persistent unsteadiness or dizziness with or without precipitating PPPD. When these disorders are present alone, patients are not as greatly affected by the motion provocations of Criterion B as when PPPD exists. The strategy for differential diagnosis in these cases is to determine if Criteria A-D for PPPD are present and evaluate key elements of clinical histories, physical examinations, and laboratory testing to determine which conditions explain the patients’ symptoms best (i.e., PPPD alone, precipitating events alone, or both) (Criterion E).

4.4.3.1 Chronic anxiety and depressive disorders. Chronic anxiety due to generalized anxiety disorder, agoraphobia, social phobia, obsessive compulsive disorders, and traumatic stress disorders may manifest with persistent dizziness [3, 95]. Depressive disorders also may cause dizziness [57]. These disorders are diagnosed according to the latest versions of the International Classification of Diseases [95] or Diagnostic and Statistical Manual of Mental Disorders [3]. However, in neurologic, otologic, and primary care settings where patients with vestibular symptoms are most commonly encountered, simple self-report questionnaires offer a valid and efficient means of detecting psychiatric morbidity. The 7-item Generalized Anxiety Disorders Scale (GAD-7) may be used to screen for pathological anxiety [73]. The 9-item Patient Health Questionnaire (PHQ-9) may be used to screen for depression [72]. The 14-item Hospital Anxiety and Depression Scale (HADS) covers both anxiety and depressive symptoms [102]. Positive results indicate that an anxiety or depressive disorder is likely, either as the sole cause of vestibular symptoms or co-existing with PPPD [12, 79]. As described in Note 5, patients may avoid circumstances that exacerbate PPPD because of the noxious nature of persistent vestibular symptoms. This may be considered a maladaptive means of managing the disorder and does not, in and of itself, merit another diagnosis. However, moderate to severe avoidance that is associated with ruminative worries about making the condition worse, becoming incapacitated, or drawing unwanted attention to oneself may be manifestations of a phobic disorder if they repeatedly disrupt desired activities. The diagnosis of PPPD alone, a phobic disorder alone (e.g., agoraphobia, social phobia, specific phobia of dizziness) or both depends on the extent to which patients’ symptoms fulfill criteria A-D for PPPD and criteria for the phobic disorder [3, 95].

A history of troubling life circumstances or recent stressful events cannot be used as evidence for or against the presence of functional or psychiatric diagnoses, including PPPD [24]. A recent study found that childhood and adulthood adversity were equally prevalent in patients with structural versus functional or psychiatric causes of vestibular symptoms [69]. Furthermore, panic disorder and generalized anxiety disorder frequently occur in the absence of identifiable stressors [3, 95]. Therefore, a diagnosis of PPPD rests on fulfillment of its diagnostic criteria, regardless of patients’ histories of adversity.

4.4.3.2 Postconcussive syndrome. Patients with postconcussive syndrome following a traumatic brain injury or whiplash often experience chronic dizziness in addition to headache, insomnia, cognitive symptoms, and mood lability [32]. Patients who fulfill all of the diagnostic criteria for PPPD after a traumatic brain injury or whiplash should receive the diagnosis. The presence or absence of other sequelae of injury will determine if additional diagnoses are warranted. On the other hand, patients who complain of chronic dizziness after head injury should not be given a diagnosis of PPPD if they do not manifest Criteria A-D.

4.4.3.3 Autonomic disorders. Autonomic disorders frequently cause dizziness. The autonomic disorders most likely to precipitate PPPD, based on research from CSD [77], are postural orthostatic tachycardia syndrome (POTS) and type 1 neurocardiogenic (vasovagal) syncope, which are most often encountered in adolescents and young adults. Orthostatic intolerance with or without hypotension from neurologic and cardiovascular illnesses (e.g., autonomic neuropathy) is more common in older adults, in whom it may be part of multi-factorial dizziness. Patients with POTS, neurocardiogenic syncope, and other autonomic disorders tend to have more pronounced orthostatic and exertional dizziness than those with PPPD [77]. However, symptoms overlap considerably, so the differential diagnosis depends on examination of autonomic integrity. PPPD does not cause abnormal changes in heart rate or blood pressure. Autonomic disorders do not create difficulties with complex or moving visual stimuli in patients who are sitting still. Thus, vital signs during autonomic challenges and sensitivity to visual stimuli when seated at rest best distinguish PPPD from autonomic disorders, recognizing the potential for the two problems to co-exist.

4.4.4 Other chronic vestibular syndromes

Chronic vestibular syndromes in the differential diagnosis of PPPD include bilateral vestibulopathy [45], neurodegenerative disorders (e.g., downbeat nystagmus syndrome and other cerebellar diseases) [61, 89], and mal de debarquement syndrome (MdDS) [19].

4.4.4.1 Bilateral vestibulopathy. Bilateral vestibulopathy is best distinguished from PPPD by its characteristic findings on physical examination and laboratory testing [45], such as bilaterally positive head thrusts and diminished responses on head impulse testing, caloric irrigation, or sinusoidal stimulation in a rotary chair. Clinical history may offer additional clues, but these are not as definitive. For example, PPPD does not cause oscillopsia, but oscillopsia is present in only 30–40% of patients with bilateral vestibulopathy. Individuals with PPPD are susceptible to symptom exacerbations when exposed to complex visual stimuli even when sitting still, whereas patients with bilateral vestibulopathy have minimal symptoms when seated and stationary.

4.4.4.2 Chronic neurologic disorders. Neurodegenerative disorders that affect posture and gait such as Parkinson’s disease, cerebellar degeneration [61], including the downbeat nystagmus syndrome [89], and small vessel white matter disease [2, 66] may manifest with dizziness or unsteadiness when standing or walking before motor signs can be detected on physical examination. The gradual onset of these complaints in the relative absence of difficulties with complex or moving visual stimuli should arouse suspicion that PPPD is not the correct diagnosis. The best approach in this situation is a period of prospective monitoring (typically 6–12 months) with a symptom log kept by the patient and serial examinations performed by the clinician before making a definitive diagnosis.

Bilateral peripheral neuropathy and orthostatic tremor [16, 101] may cause or contribute to dizziness and unsteadiness when patients are upright, though neither one causes trouble with complex or moving visual stimuli. Peripheral neuropathy is much more likely to manifest with sensory loss and pain, or present as one part of a multi-factorial picture, than to be the sole cause of dizziness. Orthostatic tremor typically causes discomfort when standing still (e.g., standing in line at a supermarket). Symptoms are relieved by walking or sitting down. Orthostatic tremor is diagnosed by identifying its characteristic 13–18 Hz tremor in the lower legs on electromyographic or posturographic testing [16, 101].

4.4.4.3 Mal de debarquement syndrome. Mal de debarquement syndrome (MdDS) [19] is a condition of persistent unsteadiness triggered by traveling on boats, aircraft, or automobiles, usually for at least a few hours. Symptoms characteristically decrease during passive motion (e.g., riding in a car) and then increase again when motion ceases. That is opposite the pattern found in most patients with PPPD, though a minority of individuals with PPPD experience temporary decreases in symptoms during modest motion, such as walking at a medium pace or riding a bicycle on a smooth path. A “spontaneous onset” version of MdDS has been described, though most patients in those reports had migraine or anxiety disorders [19], which are known precipitants of PPPD. A major difference between MdDS and PPPD is the extent of treatment response. MdDS generally has a limited response to vestibular habituation exercises or medications, whereas treatment studies of PPV [86], SMD [42, 92], VV [62, 64], CSD [81], and PPPD, itself [84], showed significant improvements with vestibular habituation or serotonergic antidepressants.

4.4.5 Adverse effects of medications

Prescription medications, over the counter preparations, and dietary supplements may cause dizziness, unsteadiness, or vertigo. Vestibular symptoms caused by newly administered medications or changed doses of existing medications may precipitate PPPD.

4.4.6 Other functional forms of vestibular symptoms

Clinicians may encounter patients who describe persistent vestibular symptoms that do not fit the diagnostic criteria of either PPPD or other well-defined chronic vestibular syndromes [24]. Examples include constant, invariant vertigo, unsteadiness, or dizziness, complex body motions in multiple directions simultaneously, and kaleidoscopic swirling movements of large portions of the visual field. Patients with these complaints often report a lack of provoking or mitigating factors. These clinical presentations have not been studied systematically, but their continuous nature, unwavering intensity, and abnormal complexity distinguish them from the episodic or fluctuating symptoms reported by patients with structural deficits, PPPD, and anxiety or depressive disorders that cause vestibular symptoms [24]. In many patients, these functional forms of vestibular symptoms are accompanied by other chronic physical complaints such as fatigue and pain, raising the possibility that they are but one manifestation of a broader somatic symptom disorder [3] or bodily distress disorder [96].

4.4.7 Gait disorders, falls, and near falls

Patients with PPPD may report sensations of veering from side-to-side when walking. On exam, they may exhibit a mildly slow or cautious gait. One study of walking mechanics found that patients with PPV walked slower, had reduced stride length, and spent a greater fraction of time with both feet on the ground than healthy subjects [71]. These changes correlated with reduced balance confidence. A case study distinguished gait and posture symptoms of CSD from those of functional gait disorders [34]. Falls and near falls have never been a part of PPV or CSD [24]. Therefore, clinical evidence of significant changes in gait or recurrent falls or near falls indicates the presence of a structural or functional gait disorder. PPPD may co-exist with these disorders.

4.5.1 Estimates of the prevalence of PPPD

Clinical epidemiologic data from tertiary care centers with special interest in PPV [13] and CSD [79] showed their prevalence to be 15–20% among all patients presenting for evaluation of vestibular symptoms, making them the most common diagnoses among young adults and the second most common among all adults, trailing only BPPV. The average duration of illness at the time of tertiary consultation was 4.5 years with some patients experiencing symptoms for decades [13, 79]. Disability varied widely from individuals who had few limitations in daily functioning to those who were severely impaired and unable to work. The average age of patients presenting for evaluation of PPV, CSD, and PPPD is the mid-40 s, with a range from adolescence to late adulthood [10, 100]. A female predominance has been reported in the first clinical reports on PPPD [10, 100].

4.5.2 Estimates of the incidence of PPPD

The incidence of PPPD following neuro-otologic precipitants may be estimated from studies that followed patients prospectively after bouts of acute or episodic vestibular disorders (e.g., vestibular neuritis, BPPV, vestibular migraine, Menière’s disease) [7, 30]. These investigations found PPPD-like chronic dizziness [7, 30] or persistent VV [23] in about 25% of patients after 3–12 months of follow-up, despite otherwise adequate compensation or recovery from the initial illnesses. These results indicate that PPPD is likely to develop in a significant proportion of patients afflicted with acute or episodic vestibular syndromes. Similar prospective studies of clinical outcomes following other medical and psychological precipitants of PPPD have not been conducted. However, retrospective investigations found that the course [80] and treatment response [78] of patients with CSD precipitated by anxiety disorders mirrored that of patients with CSD precipitated by acute vestibular conditions, suggesting that the clinical course of PPPD may be similar regardless of precipitant. A long-term follow-up study of patients with PPV found that only a minority experienced spontaneous resolution of symptoms [36]. Most had a chronic waxing and waning course and three-quarters developed anxiety or depressive comorbidity. Thus, the majority of patients with PPPD are likely to remain symptomatic without treatment, regardless of initial precipitant.

The incidence and prevalence of PPPD in primary care practices and the general population are not known as detailed epidemiologic studies of PPV, SMD, VV, and CSD have not been conducted in those settings.

4.6.1 Possible risk factors

In their original paper, Brandt and Dieterich made the clinical observation that patients with PPV were likely to have obsessive compulsive personality traits [13]. Subsequent studies using formal psychometric measures found that individuals with the anxiety-related personality traits of neuroticism and introversion [76] had an increased risk for CSD. High neuroticism also was identified in a report on PPPD [100]. In contrast, persons demonstrating resilience, optimism, and beliefs that life is meaningful and manageable had a reduced risk of persistent dizziness after acute vestibular events [85]. Patients with family or personal histories of anxiety disorders pre-dating the onset of vestibular symptoms had an increased risk of developing persistent dizziness [7] or CSD [80] after precipitating events. In patients with anxiety disorders, a history of previous vestibular deficits was associated with SMD [38, 41]. These studies suggest that anxiety-related personality traits or a personal or family history of anxiety disorders may be risk factors for developing PPPD following relevant precipitants.

4.6.2 Initial reactions

Three prospective studies found that high anxiety about dizziness during and after bouts of acute vestibular neuritis or BPPV predicted continued dizziness three [30], six [23], and twelve [28] months later. These initial psychological responses had far greater effects on long-term outcomes than the initial or subsequent states of patients’ peripheral vestibular functioning or vestibulo-ocular reflexes. Furthermore, patients with emerging symptoms of CSD who were treated with three sessions of cognitive behavioral therapy started within 8 weeks of precipitating events had marked reductions in dizziness and avoidance of provocative circumstances [26], benefits that endured at follow-up six months later [52]. Collectively, these data raise the possibility that a highly anxious response to precipitating events may be the pivotal initial pathophysiologic process in the development of PPPD, and that early symptom-specific interventions might counter this effect.

4.6.3 Possible alterations in postural control

Several investigations showed that patients with PPV manifested an alteration in postural control characterized by high frequency, low amplitude postural sway related to co-contraction of lower leg muscles when standing at rest [46, 98]. One study of patients with CSD demonstrated similar results [59]. Investigations conducted in normal, healthy people found that they used this high demand postural control strategy only in challenging balance situations such as standing at heights [1, 18]. Patients with PPV adopted this strategy during less demanding tasks than normal individuals [33, 71], possibly related to a lower threshold for engaging closed loop feedback mechanisms to adjust posture [98]. Brandt et al. [14] reported the case of a patient who was followed prospectively from a bout of acute vestibular neuritis to the development of PPV. The transition to chronic symptoms coincided with emergence of the high frequency, low amplitude sway pattern of PPV. Future studies will have to measure the prevalence of this postural control strategy among patients with PPPD and determine its association with clinical characteristics of the disorder, particularly postural symptoms.

4.6.4 Possible association with visual dependence

Bronstein and colleagues [15, 63] showed that people with VV manifested visual dependence, a trait-like tendency to rely on visual information for spatial orientation. In a prospective study, Cousins et al., [23] found that patients who had persistent dizziness for at least six months following bouts of acute vestibular neuritis had greater visual dependence than those who recovered without chronic symptoms. Redfern et al. [70] found that patients with anxiety disorders and SMD had greater body sway in response to moving visual surrounds than patients with anxiety disorders but no SMD and also than normal controls. Future studies will have to measure the prevalence and severity of visual dependence in patients with PPPD and determine its association with clinical features of the disorder, particularly visual symptoms.

4.6.5 Possible changes in activity and connectivity of crucial brain regions

The first neuroimaging studies of patients with CSD [37] and PPPD [88] were completed recently. The first study [37] measured the activity and connectivity of vestibular, visual, and anxiety-related regions of the brain using functional magnetic resonance imaging (fMRI) in response to sound-evoked vestibular stimulation in patients with CSD versus normal control subjects matched for anxiety-related personality traits. Patients with CSD showed reduced stimulus-related activity in the parieto-insular vestibular cortex (PIVC), anterior insula, inferior frontal gyrus, hippocampus, and anterior cingulate cortex compared to normal individuals. They also had more negative connectivity between the PIVC and the anterior insula, anterior cingulate cortex, and hippocampus, as well as between the anterior insula and middle occipital cortex. The second study [88] compared women with PPPD to women who had recovered without sequelae from illnesses that caused acute vestibular symptoms (i.e., typical precipitants of PPPD). Using fMRI, the authors found that women with PPPD had less activation of the anterior cingulate cortex, which was related to state anxiety, and less activation of the precuneus, which remained after controlling for psychological variables, in response to a non-motion stimulus of standardized pictures designed to elicit negative emotions. These early results suggest that brain areas responsible for high level spatial orientation, multi-sensory integration, and threat assessment may not be as active or well connected in patients with PPPD as in normal people, potentially leaving lower level posture and gaze control mechanisms poorly integrated with one another. These findings await confirmation in larger studies with sufficient power to control for potential confounds and measure associations with clinical aspects of PPPD.