CASE REPORT Year : 2022  |  Volume : 28  |  Issue : 3  |  Page : 249-251

Profiling vestibular evoked myogenic potentials findings in cerebellar disorders

Varsha Nattamai Satish Babu, Aishwarya Narayanan
Department of Audiology and Speech Language Pathology, SRM Medical College Hospital and Research Center, SRM Institute of Science and Technology, Chennai, Tamil Nadu, India

Date of Submission28-Jun-2021Date of Decision07-Jun-2022Date of Acceptance05-Aug-2022Date of Web Publication21-Nov-2022

Correspondence Address:
Ms. Aishwarya Narayanan
No. N-1, Sudarsan Gardens, 106, Velachery Road, Guindy, Chennai - 600 032, Tamil Nadu
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/indianjotol.indianjotol_93_21

Cerebellar dizziness is a common clinical sign in patients with cerebellar dysfunction with several multifaceted consequences in the life of an individual. The clinical diagnosis of this type of dizziness is delayed or overlooked as its frequency is underestimated. Inaccurate examination of the vestibular or ocular motor systems contributes to this effect. However, with expansion of use of ocular vestibular evoked myogenic potentials (oVEMPs) in the diagnosis of central disorders, makes it an important tool used in routine practice. The present study shows that oVEMP is majorly affected in various cerebellar disorders, making it a sensitive test to be used in suspected patients. Based on the vestibular evoked myogenic potential results and complete audiological profile in the patients with cerebellar demyelination and cerebellar atrophy, medical team was able to arrive at a diagnosis when the radiological findings were inconclusive. This study shows that oVEMPs are neurological responses, sensitive to cerebellar dysfunction.

Keywords: Cerebellar atrophy, cerebellar demyelination, cerebellar dizziness, differential diagnosis, ocular vestibular evoked myogenic potential

How to cite this article:
Babu VN, Narayanan A. Profiling vestibular evoked myogenic potentials findings in cerebellar disorders. Indian J Otol 2022;28:249-51
  Introduction 

Cerebellar dizziness is a classical neurologic sign seen in patients with cerebellar dysfunction. In one-third of the patients, it may be caused due to ocular motor dysfunction, and in one-fifth of the patients, it may be caused due to Down beating nystagmus (DBN) syndrome.[1] For this reason, a complete evaluation of the ocular motor and vestibular systems is warranted.

The findings summarized in this article suggest how ocular vestibular evoked myogenic potential (oVEMP) is beneficial in diagnosing cerebellar disorders when imaging results cannot detect functional abnormalities.

  Case Report 

Audiological findings of two patients with different cerebellar pathologies have been profiled below. The evaluations consisted of pure tone audiometry (PTA) that tested both air conduction threshold across 250 Hz, 500 HZ, 1000 Hz, 2000 Hz, 4000 Hz, and 8000 Hz and bone conduction threshold across 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz. The average of thresholds at 500 Hz, 1000 Hz, and 2000 Hz has been reported as the pure tone average. The pure tone thresholds were also correlated with the speech recognition thresholds (SRTs) and speech identification scores (SISs). The immittance testing included the tympanogram with reflex thresholds. Furthermore, auditory brainstem responses–site of lesion (ABR-SoL) testing was used to rule out the presence of any retrocochlear pathology. For vestibular evaluations, behavioral vestibular tests (Romberg, high-frequency head shake, head impulse test, and vestibular occular reflex suppression) to differentiate between peripheral and central lesions were used along with vestibular evoked myogenic potential (VEMP) (both cervical and ocular). Tone burst stimuli of 500 Hz was used to elicit the VEMP responses at 112 dB and with repetition rate of 5.1/s. Two runs for each ear was taken into consideration for analysis of replicability.

Case 1

A 36-year-old patient had reported to the department with a complaint of giddiness. She had been experiencing true vertigo for 1 month. Progressive giddiness was informed to be sudden in onset and worsened while standing or walking compared to sitting. Nausea was reported following each episode of giddiness which lasted for about 2–3 min while standing or walking alone. The patient had difficulty walking or standing due to dizziness and imbalance concerns. No other complaints were recorded. From her medical findings, it was known that she has been undergoing physiotherapy for cervical spondylosis. Magnetic resonance imaging (MRI) brain with contrast showed no significant abnormalities.

A series of audiological tests were done. PTA and speech audiometry showed normal findings. Immittance audiometry also revealed no indication of middle ear pathology, with all reflexes present. ABR-SoL showed no indication of retrocochlear pathology. Cervical VEMP (cVEMP) peaks, P13 and N23, were obtained within normal latency limits, with good replicability in both ears. These findings indicated normal functioning of the sacullocollic pathways. On the contrary, in the oVEMP testing, N10 and P15 peaks were not observed in both ears, indicating a dysfunction of the utriculo-ocular pathways. With the help of the clinical signs and symptoms and audiological findings, neurologist and otorhinolaryngologist suspected the patient to be a case of cerebellar demyelination.

Case 2

A female aged 58 years had complained of progressive dizziness. The concern increased when the disequilibrium caused the patient to fall. A feeling of imbalance and sway toward left was reported with the presence of reduced hearing sensitivity for 2 years that was progressive in nature. No other complaints were reported. MRI brain revealed diffuse cerebellar atrophy and asymmetry of vertebral arteries in the left vertebral artery.

A range of subjective and objective audiological tests was conducted. PTA results showed mild sensorineural hearing loss in the right ear and moderately severe sensorineural hearing loss in the left ear. Immittance audiometry indicated the absence of middle ear pathology. ABR-SoL findings showed no retrocochlear pathology. cVEMP indicated normal sacullocollic pathway functioning in both ears, while oVEMP showed bilateral dysfunction of utriculo-ocular pathway.

  Discussion 

Cerebellum plays an active role in otolith signal modulation, and the most traditional vestibular tests only check the inhibitory responses of the cerebellum on vestibular nuclei. However, the oVEMP evaluates the excitatory crossed Vestibulo-ocular reflex (VOR) pathway with the responses primarily originating from the otolith organs. The presence of strong direct projections from the utricular afferent pathway to vestibular nuclei, cerebellar nodulus, and ventral uvula accounts for why the lesion in these areas impair the VOR and hence, the oVEMP.[2] Thus, abnormalities in VEMP can be associated to impaired modulation of cerebellum in otolith functioning. This article describes two case reports that highlight the usefulness of including VEMP in the test battery.

Case 1

Cerebellar demyelinations cause damage of myelin sheath in the cerebellum causing balance impairments. Such patients present with severe giddiness and disequilibrium issues that are progressive in nature. It is not detected by MRI or advanced imaging. On the contrary, cVEMP and oVEMP have been found to be more sensitive because of the involvement of vestibulo-collicular and vestibulo-occular pathways in cerebellar demyelination.[3] In relation to cVEMP, prolonged peak latencies and reduced amplitudes have been reported in some patients due to the presence of axonal damage that causes reduction in signal conduction.[4] It was noted to improve over time with treatment.[5] In the present article, however, the latencies and amplitudes were within the normal limits. On the other hand, the absence of oVEMP responses was noted, indicating the presence of cerebellar involvement. Similar findings were present in other patients with demyelinating diseases of CNS.[5]

Among both VEMPs, oVEMP shows more abnormal results because it involves responses of the utricle through which the vestibulo-cerebellum receives and sends signal. Any disinhibition in this part of the cerebellum causes disruption in the modulation of the otolith-ocular response.[2] In addition, hearing and behavioral vestibular evaluation helped in diagnosing this condition. Hearing remains unaffected in these patients, which was observed in this case as well. The information gathered during the case history interview and the inability to perform the central behavioral vestibular tests were other indicators of a possible cerebellar disorder. These findings aided in directing medical team toward the diagnosis of cerebellar demyelination.

Case 2

Diffuse cerebellar atrophy causes a reduction in the volume of cerebellum which usually occurs due to hereditary ataxia, ageing, drugs, multiple system atrophy, cerebellitis, Gordon Holmes syndrome, Fahr disease, Marinesco-Sjogren syndrome, and various other disorders. Cerebellar atrophy is often confused with global cerebellar hypoplasia as both disorders share similar symptoms such as the presence of sensorineural hearing loss. However, latter is a congenital disorder and is often accompanied with cerebral palsy and intellectual disability. In this case, atrophy has been attributed to aging-related changes as no other significant cause was identified clinically and because it was progressive in nature. Although these patients experience giddiness and disequilibrium, very few studies were done using VEMP and the findings showed that responses remain unaffected as the peripheral otolith organs function normally.[6] However, an effect on oVEMP is seen in later stages as it begins to affect the vestibulo-cerebellar pathways. The progressive nature of symptoms can also be identified during case history interview (as seen in the present case) and follow-up audiological and behavioral balance assessments along with VEMP testing.

In this article, both patients had difficulties while performing behavioral vestibular assessment, indicating a central pathology involvement. It hinted the probability of cerebellar lesion when correlated with other clinical findings and careful interpretation of audiological findings. Abnormalities were detected in cVEMP and oVEMP responses. This can again be attributed to the effect of cerebellar dysfunction, relating to regulation of the otolith and occular signals. Although imaging studies can help in confirming a diagnosis, in cases such as cerebellar demyelination and neurotoxicity, significant abnormalities are not detected. It instigates a delay in appropriate treatment.

In such situations, VEMP not only helps in differential diagnosis, it is also a stress-free outpatient procedure. Easy accessibility of the testing equipment and better tolerance by patients with dizziness add to the merit. Conventional tests such as caloric test and videonystagmography (VNG) may be time-consuming and require set-up curated to specifications. Moreover, responses on caloric test will vary depending on the following factors; ear canal size, efficiency of thermal energy transfer and tolerance levels of the individuals. Rotational chairs are further gaining popularity but are not widely available due to the expense. The sensitivity of this test to detect chronic unilateral vestibular hypofunction has also been under the radar.

While this study highlights the role of VEMP, mainly oVEMP findings, in identifying disorders related to the cerebellar circuitry, it has to be replicated in larger population to arrive at a conclusion. VEMP can also be affected by factors such as the ability of the patient to maintain muscle tension, calibration of equipment, electrode placement, and interclinician variability in identifying responses. oVEMP may particularly be affected by pathological eye movements such as congenital nystagmus or opsoclonus. In such conditions, oVEMP is done immediately after a vertigo attack, which may not be possible in every situation. Careful consideration of these factors is a must when performing the test.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 

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