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EDITORIAL COMMENTARY
Year : 2021  |  Volume : 24  |  Issue : 2  |  Page : 128-129
 

Brainstem evoked potentials in the idiopathic parkinson's disease (PD)


Department of Neurology, Pacific Centre of Neurosciences, Pacific Medical College and Hospital, Rajasthan, India

Date of Submission11-Dec-2020
Date of Acceptance23-Dec-2020
Date of Web Publication05-Apr-2021

Correspondence Address:
Dr. Ajay Kumar Vats
Neurology Centre, 6-A, Block-B, Shikarbadi, Goverdhan Villas, Udaipur-313 001, Rajasthan
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/aian.AIAN_1254_20

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How to cite this article:
Vats AK. Brainstem evoked potentials in the idiopathic parkinson's disease (PD). Ann Indian Acad Neurol 2021;24:128-9

How to cite this URL:
Vats AK. Brainstem evoked potentials in the idiopathic parkinson's disease (PD). Ann Indian Acad Neurol [serial online] 2021 [cited 2021 Jun 19];24:128-9. Available from: https://www.annalsofian.org/text.asp?2021/24/2/128/313096




In this issue of the Journal, an original article, Mehra A et al., (AIAN 1022) have studied findings using cervical vestibular evoked myogenic potentials (cVEMPs) and brainstem auditory evoked potentials (BAEPs) in 25 patients with Parkinson's disease (PD), and compared the data with 25 age-matched controls, correlating the findings with the symptoms related to brainstem involvement. The authors found that PD is associated with cVEMPs and BAEPs abnormalities, suggesting the involvement of the auditory and vestibular pathways in PD. The abnormalities in the cVEMPs study appears to be a promising electrophysiological marker for the presence of REM sleep behavior disorder (RBD) and postural instability in patients with PD.

It has been recognized from the beginning that neuropathology in PD involves brain areas beyond the dopaminergic nigrostriatal system. Areas of the nervous system not directly involved in motor control like the dorsal nucleus of the vagus, brainstem raphe nucleus, hypothalamus, olfactory tubercle, limbic cortex, and neocortex are also found to have Lewy body (composed of mainly alpha-synuclein) on neuropathological examination. The pathology extends into the peripheral autonomic nervous system involving sympathetic ganglia, cardiac sympathetic afferents, and gut myenteric plexus.[1] The nonmotor symptoms of PD are attributable to the selective early alpha-synuclein accumulation in the extrastriatal regions of the brain.[2] In recent times, increasing recognition of nonmotor manifestations of PD has led to its incorporation in the current criteria proposed by the Movement Disorder Society (MDS), both for PD as well as prodromal PD and development of MDS Unified Parkinson's Disease Rating Scale (MDS-UPDRS).[3],[4],[5] Despite deposition of alpha-synuclein in the several brainstem regions in PD, there is a distinct paucity of electrophysiological markers to assess its impact, both in the motor as well as nonmotor symptoms of the disease. VEMPs and BAEPs are two potential electrophysiological tools that could provide useful insights into the brainstem dysfunction, which is ostensibly responsible for the many nonmotor symptoms of PD.

Although the ability of vestibular labyrinth (otolith organs) for getting stimulated by loud sounds is known for the past 85 years, it was Colebatch and Halmagyi in 1992, who were first to record muscular activity by stimulating the Otolith organs by an auditory stimulus[6] and since then VEMPs studies have become an integral part of the vestibular test battery. Initially, the VEMPs were recorded from the sternomastoid muscle ipsilateral to the ear subjected to an auditory stimulus, and this is called cervical VEMP (cVEMP). It was later found that a reliable myogenic potential is recordable from the inferior oblique muscle contralateral to the ear subjected to the auditory stimulus, and this is known as ocular VEMP (oVEMP). The VEMP studies (both oVEMP and cVEMP) are primarily used in the evaluation of peripheral vestibular disorders attributed to the dysfunction of otolith organs (utricle and saccule). However, in certain conditions involving the brainstem (e.g., infarction, demyelination), the abnormalities in VEMP are occasionally found if the reflex arc of the vestibulo-collic reflex is involved, and these include prolongation of latencies, reduced amplitude, and rarely complete absence of the response.[7]

The motor and non-motor symptoms (NMSs) of PD are attributed to the degeneration of several brainstem nuclei consequent to alpha-synuclein accumulation caudo-cranially, from the dorsal motor vagal nucleus in the medulla through brainstem to the neocortex.[8],[9] This results in a functional misconnection between the brainstem and higher structures involving mainly non-dopaminergic pathways even in the earliest phase of the disease. The abnormalities in VEMPs and BAEP's are potential biomarkers of brainstem dysfunction and its associated motor and NMSs. Therefore, VEMPs and BAEP might represent a valuable tool for the assessment of NMSs of the brainstem dysfunction such as neuropsychiatric disturbances, daytime sleepiness, dysautonomia, RBD, gastrointestinal disorders, and depression in PD. Since the NMSs in the PD antedates clinical manifestations of the motor symptoms of PD by years or even decades, their early recognition by electrophysiological markers may turn out to be a critical target for framing diagnostic paradigms and identifying the at-risk populations.



 
   References Top

1.
Kim HJ. Alpha-synuclein expression in patients with Parkinson's disease: A clinician's perspective. Exp Neurobiol 2013;22:77-83.  Back to cited text no. 1
    
2.
Poewe W. Non-motor symptoms in Parkinson's disease. Eur J Neurol 2008;15(Suppl 1):14-20.  Back to cited text no. 2
    
3.
Postuma RB, Berg D, Stern M, Poewe W, Olanow CW, Oertel W, et al. MDS clinical diagnostic criteria for Parkinson's disease. Mov Disord 2015;30:1591-601.  Back to cited text no. 3
    
4.
Fahn S, Elton RL, UPDRS program members. Unified Parkinsons disease rating scale. In: Fahn S, Marsden CD, Goldstein M, Calne DB, editors. Recent Developments in Parkinsons Disease, vol 2. Florham Park, NJ: Macmillan Healthcare Information; 1987. p. 153–63.  Back to cited text no. 4
    
5.
Goetz CG, Tilley BC, Shaftman SR, Stebbins GT, Fahn S, Martinez-Martin P, et al. Movement disorder society-sponsored revision of the unified Parkinson's disease rating scale (MDS-UPDRS): Scale presentation and clinimetric testing results. Mov Disord 2008;23:2129-70.  Back to cited text no. 5
    
6.
Colebatch JG, Halmagyi GM. Vestibular evoked potentials in human neck muscles before and after unilateral vestibular deafferentation. Neurology 1992;42:1635-6.  Back to cited text no. 6
    
7.
Biswas A. VEMP Vestibular evoked myogenic potentials and other tests to evaluate otolithic functions. Mumbai, Publishers Medilinks; 2015.  Back to cited text no. 7
    
8.
Braak H, Del Tredici K, Rüb U, de Vos RA, Jansen Steur EN, Braak E. Staging of brain pathology related to sporadic Parkinson's disease. Neurobiol Aging 2003;24:197-211.  Back to cited text no. 8
    
9.
Braak H, Rüb U, Gai WP, Del Tredici K. Idiopathic Parkinson's disease: Possible routes by which vulnerable neuronal types may be subject to neuroinvasion by an unknown pathogen. J Neural Transm (Vienna) 2003;110:517-36.  Back to cited text no. 9
    




 

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