ABSTRACT & COMMENTARY
The Relationship Between REM Sleep Behavioral Events and Parkinson’s Disease
By Matthew R. Ebben, PhD
Assistant Professor of Psychology in Clinical Neurology, Center for Sleep Medicine, Weill Medical College of Cornell University
Dr. Ebben reports no financial relationships relevant to this field of study.
This large-scale polysomnographic study demonstrated that the prevalence of REM sleep behavioral events in unmedicated patients with newly diagnosed Parkinson’s disease is higher than in healthy controls.
Sixel-Doring F, et al. Rapid eye movement sleep behavioral events: A new marker for neurodegeneration in early Parkinson disease? Sleep 2014;37:431-438.
REM sleep behavior disorder (RBD) was first proposed as a clinical sleep disorder in the mid-1980s by Schenck, who described patients acting out dreams in the context of REM sleep. This condition is most common in males over the age of 50, particularly in the sixth and seventh decade of life. It is now well known that α-synucleinopathies, such as multiple systems atrophy, Lewy body dementia, and Parkinson’s disease (PD), have a strong association with RDB. In fact, 50-80% of idiopathic RBD patients will develop an α-synucleinopathy within 10-15 years. However, few large-scale polysomnographic (PSG) studies have investigated the prevalence of RBD in newly diagnosed and unmedicated PD cases, which is the focus of this study. Moreover, most previous investigations have concentrated on violent dream enactment, whereas the Sixel-Doring study includes subtle purposeful movements in REM sleep as well as REM sleep without atonia (RWA) in their investigation.
Subjects included men and women between the ages of 40-85 years with a diagnosis of PD based on the UK Brain Bank Criteria. PD subjects were compared to neurologically healthy controls (HC) matched by age, sex, and educational level. Exclusion from the PD group included severe vascular encephalopathy or normal pressure hydrocephalus on MRI, multiple system atrophy, progressive supranuclear palsy, medication-induced PD, and/or past treatment with antipsychotic drugs. Exclusion from the HC group included a history of a central nervous system disorder in self or a close relative, evidence of cognitive decline (Mini-Mental State Examination [MMSE] < 26), and/or a current sleep disorder.
Both HC and PD groups were given two PSGs; when possible, the second recording was used for analysis. Investigators reviewed and documented videos from the subjects for visible movements and vocalizations. All purposeful movements and noises were classified as REM sleep behavioral events (RBE). Surface electrodes on the mentalis muscle quantified RWA. The number of 3-second groups with elevated muscle tone within a 30-second epoch of sleep was used to gauge the degree of RWA in each subject. An RBD screening questionnaire was used to assess history of RBD.
In addition to PSG, each subject also had a neuropsychological assessment that included tests of executive function, attention, speech, verbal fluency, memory, and visual spatial function.
A total of 159 subjects with PD and 110 HC were used for analysis. In the PD group, 25% had purposeful movements and/or vocalizations as well as increased mentalis activity in REM sleep qualifying them as definite RBD, compared to 2% of HC. This finding was not statistically significant. In subjects without behaviors during REM sleep, 4% in the PD group and 2% of the HC showed RWA (not significant). On the measure of RBE, 51% of PD subjects and 15% of HC were found to be positive (P < 0.001). REM latency was significantly longer in the PD vs HC groups (P = 0.003). However, no other sleep parameters were significantly different between groups.
MMSE, clock drawing, and odor identification scores were significantly worse in the PD with RBE vs PD without RBE groups. Tremor, UPDRS (subscale 3), postural instability/gait disorder, and Hoehn and Yahr stage were not significantly different between groups.
Neuropsychological assessments revealed that PD + RBE group had significantly worse verbal fluency (both semantic and lexical) and memory, as well as spatial ability, similarity discrimination, and Stroop interference compared to the HC-RBE group.
COMMENTARY
This study found that a higher number of PD subjects had RBE events (51%) compared to definite RBD (25%). Neuropsychological assessment of the PD with RBE group showed a broad decrement in function over the HC without RBE group. However, a higher number of HC subjects were also found to have RBE (15%) compared to definite RBD (2%). The authors of this paper had no explanation for the high percentage of normal controls with RBE. It will be important to follow these subjects prospectively to see if they convert to PD. Nonetheless, this suggests that RBE events can be used as part of an assessment for PD, but should not be used independently as a diagnostic tool for PD. More importantly, this study suggests that patients found during polysomnographic testing to have purposeful movements during REM sleep, not quite rising to the level of definite RBD, should be evaluated for PD.
