The patient journey for vestibular assessment can be a lengthy process. A 2011 survey by the Vestibular Disorders Association (VEDA) states that, on average, patients consult four to five doctors before receiving a diagnosis. Furthermore, it takes an average of three to five years for a person with a vestibular disorder to receive a diagnosis (VEDA, 2011). By applying new testing techniques, clinicians can scale down their workflow and obtain an accurate diagnosis in less time. The article, “A Streamlined Approach to Assessing Patients with Peripheral Disorders,” featured in the September/October 2015 issue of Audiology Today, presented a comprehensive review of the assessment process for peripheral vestibular disorders. The authors proposed management modification through changes to the current, widely accepted, protocols for testing that center around videonystagmography and electronystagmography (VNG and ENG, respectively).
The effectiveness of vestibular assessment has been improved by technological developments such as the video head impulse test (vHIT) that can provide unique insights to differential diagnosis. The vHIT itself has been a major development in the area of vestibular development as it has allowed the evaluation of all six semicircular canals independently. The diagnostic utility of the vHIT has been further increased by technological advances allowing unique insight in the central vestibular function. Originally released in 2013 with only vHIT capability, the ICS Impulse® has since been enhanced with additional technological advances and made available to audiologists in the United States following Food and Drug Administration clearance of the ICS Impulse Oculomotor and Positional modules.
As recently as September 2016, the ICS Impulse was again updated to include the Suppression Head Impulse Paradigm (SHIMP), which was introduced at the Barany Society meeting in June, 2016. The SHIMP tracks the presence of anti-compensatory saccades after a head turn. These results can support residual vestibular function (MacDougall, et al, 2016). Initial reports of SHIMP results focuses on findings for those with normal vestibular function, unilateral vestibular loss, and bilateral vestibular loss (MacDougall, et al, 2016) where, “in all participants, SHIMP [and vHIT] resulted in a reversed saccadic pattern.” This means that healthy controls with normal vestibular function showed few catch-up saccades with vHIT, whereas testing with SHIMP demonstrated large negative saccades. Conversely, patients with bilateral vestibular loss showed frequent overt saccades during vHIT but few saccades during SHIMP. In comparison, patients with unilateral vestibular loss demonstrated covert saccades when vHIT was performed to the affected side, with large downward saccades to the healthy side during SHIMP. While more work needs to be done to better understand the clinical utility of SHIMP and its relation to the vHIT test, the initial results are indeed promising.
While peripheral vestibular disorders can commonly account for many causes of vertigo, as many as 23 percent of patients with dizziness in a recent study cohort had a central etiology to their vertigo (Mostafa et al, 2014). When considering the desired workflow for assessing a dizzy patient, the first step for many professionals is a thorough case history. Patients who likely have a central etiology to their vertigo may present with the following: nystagmus (most often purely vertical or torsional) that does not suppress with visual fixation, short latency of nystagmus after provocation and nystagmus that is less prone to fatigability, a longer history of symptoms, possible loss of consciousness, other neurological symptoms, and possibly the absence of other otological symptoms (Jacobson and Shepard, 2009; Shepard, 2009). However, as discussed later in this article, symptoms such as the rapid onset of vertigo, motion intolerance, horizontal nystagmus, and fluctuating hearing loss can be found in both central and peripheral disorders, and does not make an initial impression abundantly clear (Kattah et al, 2009; Shepard, 2009). This ambiguity can only be resolved by a judicious use of clinical judgement and the latest diagnostic tools. The reader is directed to Signs and Symptoms of Central Vestibular Disorders (Shepard, 2009) for further information about determining central versus peripheral etiology of vertigo. In the remainder of the article, we provide an in-depth review of the latest development in balance assessment technologies that are helping audiologists and other balance care professionals reduce the time it takes to test patients with Wernicke’s encephalopathy, Vestibular Schwannoma, and Vestibular Migraine, as examples of central pathology.
Often associated with alcohol abuse or malnutrition, Wernicke’s encephalopathy occurs when thiamine (vitamin B1) deficiency causes patients to experience oculomotor abnormalities (including nystagmus), ataxia, and altered mental status (Kattah et al, 2013; Szmulewicz et al, 2011). However, it is possible for at least one of these to be absent (Szmulewicz et al, 2011). Patients with thiamine deficiency may report loss of weight over the past year, poor nutrition with high carbohydrate intake, recurrent vomiting episodes over the past month, loss of appetite, fatigue, weakness, double vision, giddiness, insomnia, anxiety, difficulty concentrating, and memory loss (Kattah et al, 2013). It should be noted that in the referenced study, weight loss ranged from 120–157 pounds and was secondary to gastric bypass surgery for the three participants who had experienced weight loss, and the weight loss was not a symptom of its own or unrelated to a potential cause for malnutrition.
FIGURE 2 presents a modified workflow for Wernicke’s encephalopathy. Within each of these subtests, clinicians can expect the following findings:
- Gaze-Evoked/Spontaneous Nystagmus: A nystagmus pattern that supports central etiology (gaze-evoked nystagmus that is typically central positional horizontal nystagmus bilaterally, sometimes vertical nystagmus).
- VOR: Cerebellar damage will present as catch-up saccades to head movement at slow velocities and failure of VOR suppression (VORS).
- Impulse: vHIT will show catch-up saccades that may be present for all six semicircular canals, with abnormality more likely noted for the horizontal semicircular canals. However, if the patient has had thiamine repletion treatment, the abnormal vHIT may recover (Kattah et al, 2013).
Of note, Wernicke’s encephalopathy is one of three major differential diagnoses of cerebellar ataxia with neuropathy and bilateral vestibular areflexia syndrome (CANVAS). The clinical hallmark of this disorder would be impaired visual enhanced VOR (VVOR). These patients can also present with gaze-evoked horizontal or downbeat nystagmus, saccadic smooth pursuit, gait ataxia, dysarthria, and appendicular ataxia (Szmulewicz et al, 2011). A consideration for differentiating between Wernicke’s encephalopathy and CANVAS, based on the literature reviewed, is that all patients with CANVAS had catch-up saccades for both horizontal and vertical canal testing, whereas this was not as consistently presented with Wernicke’s encephalopathy (Kattah et al, 2013; Szmulewicz et al, 2011).
Vestibular schwannoma (VS) is a slow-growing and benign tumor that presents with unilateral progressive hearing loss, tinnitus, and dizziness, which can vary based on the size of the tumor. Furthermore, because the tumor is slow-growing, vestibular function diminishes but is often compensated for, and the perception of vertigo or vestibular dysfunction is more commonly seen in larger tumors (Batuecas-Caletrio et al, 2015). Patient symptoms will reflect the above clinical presentations (i.e., perception of asymmetric hearing loss).
FIGURE 3 illustrates the suggested workflow for vestibular schwannoma. One should expect the following findings:
- Audiogram: Unilateral sensorineural hearing loss to the side of the lesion.
- Gaze-Evoked/Spontaneous Nystagmus: Central nystagmus (gaze-evoked, upbeat, or downbeat nystagmus; or central positional horizontal nystagmus). Bruns nystagmus (slow and large amplitude nystagmus when looking toward the side of the lesion, and rapid, small-amplitude nystagmus when looking away from the side of the lesion). Hyperventilation nystagmus if present will beat toward the side of the VS (Minor et al, 1999). Paretic head-shaking nystagmus beating away from the side of the tumor.
- VOR: Catch-up saccades to head movement at slow velocities, if cerebellar damage has occurred.
- Impulse: Catch-up saccades during vHIT that can occur on the side of the VS, as well as some abnormal findings on the unaffected side. Gain is likely to be decreased on the side of the lesion and normal for the contralateral side. Patients may also undergo caloric testing, and are likely to present with unilateral weakness on the side where the tumor is growing. The amount of canal paresis measured, as well as the gain asymmetry noted on vHIT, are both directly related to the size of the tumor (Batuecas-Caletrio et al, 2015).
Interestingly, patients who have undergone surgery for VS may not follow the pattern of results described earlier. A recent study disclosed that patients who underwent unilateral vestibular deafferentiation surgery showed more covert saccades than overt saccades in their first week of recovery (Mantokoudis et al, 2013). This same study also showed that the intensity of the slow phase velocity of spontaneous nystagmus decreased within two days of the surgery, and that when present, vertical skew deviation that was present after surgery declined within the first five days after surgery. Another study has shown that patients who are younger (mean age of 47 years) and have more vestibular deficit before surgery have better post-surgical outcomes than those who are, on average, a decade older and had less vestibular deficit before surgery (Batuecas-Caletrio et al, 2013). This study also showed that for the younger patients, covert and overt saccades always occurred in an organized fashion, whereas the older patients would have more randomized findings.
The complex relationship between migraine and vertigo has been long recognized, and patients who have vertigo and migraine are prone to experiencing vertigo, BPPV, motion sickness, and Ménière's disease (Lempert and Neuhauser, 2009). A recent publication by the Barany Society in conjunction with the International Headache Society states that for patients to be diagnosed with vestibular migraine, they must meet certain criteria. These criteria include the following: at least five episodes with vestibular symptoms of moderate or severe intensity that can last from five minutes to 72 hours, current or previous history of migraine with or without aura, and one or more migraine features with at least 50 percent of the vestibular episodes (such as headache, photophobia, phonophobia); all of which are not accounted for by another vestibular or International Classification of Headaches Disorders (ICHD) diagnosis.
Similarly, patients with probable migraine experience at least five episodes with vestibular symptoms that are not accounted for by another vestibular or ICHD diagnosis, as well as either a history of migraine or migraine features during an episode (Lempert et al, 2012). For further information on vestibular migraine diagnosis, please refer to the aforementioned document.
Careful evaluation of the patient with vestibular migraine and monitoring over time can aid in differential diagnosis, as the potential for prolonged duration of vertigo as well as other symptoms including nausea, emesis, prostration, transient auditory symptoms, and susceptibility to motion sickness, can mimic Ménière’s disease. (Lempert et al, 2012; Cherian, 2013). FIGURE 4 demonstrates a modified workflow for assessing patients with suspected vestibular migraine.
Within each of these subtests, one should expect the following findings for a patient with vestibular migraine (Otometrics, 2015):
- Gaze-Evoked/Spontaneous Nystagmus: A central nystagmus, e.g., gaze-evoked, upbeat, or downbeat nystagmus, or a central positional nystagmus. Often saccadic pursuit is observed. See FIGURE 5.
- Impulse: Typically the response will be normal but peripheral vestibular deficits may be observed and result in the presence of catch-up saccades (covert or overt). See FIGURE 6.
- VEMP: Within normal limits. Note: Some literature has reported a reduction in amplitude. See FIGURE 7.
- Calorics: Lempert and Neuhauser (2009) have reported caloric findings to show unilateral hypofunction in 10 to 20 percent of VM patients.
By using new testing techniques, clinicians can now streamline their workflow and obtain an accurate diagnosis in a shorter period of time. A streamlined process can not only increase access to care, but also provide patients the answers they need to better understand their diagnosis. We have attempted to demonstrate specific cases where the otherwise powerful V/ENG tool can be enhanced by incorporating advancements in vestibular testing into the clinical workflow.