Objective: 1. To evaluate the presence of RBD in patients with SAOA
2. To follow up patients of SAOA with RBD whether they develop multiple system atrophy-cerebellar subtype (MSA-C)
3. To follow the natural history of patients with SAOA

Background: SAOA are a group of disorders which present as slowly progressive ataxias with median survival of 21 years[1].Being a diagnosis of exclusion with no pathological hallmark or clinical criteria, the prevalence is not clearly known.These patients have additional non- cerebellar signs like spasticity, hyporeflexia in ankles, reduced vibration sense and mild urinary symptoms not fulfilling criteria for severe autonomic failure.Various studies suggest that a proportion of patients (3.8% to 24%) with SAOA can convert into MSA-C within 4-5 years[2].
MSA- C is a rapidly progressive degenerative ataxia with autonomic failure.Patients with MSA-C have more severe ataxia at presentation and also more rapid increase in annual scale for assessment and rating of ataxia (SARA) score[3].Nowhere in the diagnostic criteria of MSA, there is mention of RBD when it has been seen that 81-90% patients of spontaneous RBD will ultimately develop a synucleinopathy[4].RBD generally precedes parkinsonian disorders ( which includes MSA) by a decade. RBD detection by polysomnography in a case of sporadic ataxia, may infact predict the future development of probable MSA-C.

Method: Patients of SAOA will be subjected to autonomic function tests and polysomnography. RBD screening questionnaire, Composite Autonomic Symptom Score-31, SARA  and Montreal Cognitive Assessment scale will be done at baseline and every 6 months to look for progression of disease severity and other non-motor manifestations (cognitive, psychiatric, autonomic and sleep disorders) in SAOA.

Results: Since RBD precedes development of neurodegenerative synucleinopathies by a decade, there is a possibility that MSA-C patients of the SAOA group (if detected early by RBD) may become a subject of any trial of developing and testing disease-modifying therapies. If a sizeable proportion of patients of RBD with SAOA develop MSA-C in the long run, we plan to propose addition of RBD in the diagnostic criteria for probable/possible MSA-C.

Conclusion: The study has been undergoing at All India Institute of Medical Sciences, New Delhi since 30^th September, 2021.

References: References:
[1]. Klockgether T. Sporadic adult-onset ataxia. Handb Clin Neurol. 2018;155:217-225.
[2]. Gilman S, Little R, Johanns J, Heumann M, Kluin KJ, Junck L, Koeppe RA, An H. Evolution of sporadic olivopontocerebellar atrophy into multiple system atrophy. Neurology. 2000;55(4):527-32.
[3]. Giordano I, Harmuth F, Jacobi H, et al. Clinical and genetic characteristics of sporadic adult-onset degenerative ataxia. Neurology. 2017;89(10):1043-1049.
[4]. Howell MJ, Schenck CH. Rapid Eye Movement Sleep Behavior Disorder and Neurodegenerative Disease. JAMA Neurol. 2015 ;72(6):707-12.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/evaluation-of-rapid-eye-movement-behavioral-disorder-rbd-in-sporadic-adult-onset-ataxia-saoa-a-prospective-observational-study/