Postural Sway In Early Parkinson’s Disease And Idiopathic Rapid Eye Movement Sleep Behavior Disorder

Part1Postural sway in patients with early Parkinson’s diseaseBackground and ObjectivePostural instability is one of the most common and debilitating problems for people with Parkinson’s disease (PD). Postural instability increases with disease progression, leading to an increased risk of falling, soft tissue injuries, fractures and psychological fear of falling, which often results in a significant reduction in quality of life and life expectancy. In most cases, levodopa treatment is ineffective in restoring normal postural control. Early identification of postural instability for individuals with PD is important in order to address fall prevention.Measures of postural control have not been considered viable candidates for measurement of progression in early-to-moderate, untreated PD because postural problems are not clinically apparent at this stage. Postural problems in patients with PD in clinical trials are usually measured with the PIGD. Although the PIGD is easy to use, does not require equipment, and is quick to administer, the results obtained are subjective and are not sensitive enough to detect early disease progression.Body-worn accelerometers (ACC) have been proposed as a portable, low-cost alternative to a force plate for measurements of postural sway.Many factors have been found to be associated with falling in PD patients. In particular, the attention was focused on the possible influence of dual task performance on postural stability. Morris and colleagues demonstrated that a concomitant verbal-cognitive task significantly deteriorated postural stability in PD. Similar findings were reported by Ashburn and coworkers showing that a greater postural sway was present in faller PD patients whilst completing a distracting cognitive task.Stereopsis, or binocular depth perception, depends on the disparity between the views perceived by each eye. The two images are fused in the cerebral cortex and experienced as a single three-dimensional representation under normal circumstances. Parkinson’s disease patients are known to have deficits in the perception of visual stimuli. However, it remains unclear whether these visual deficits could lead to dysfunction of stereopsis.In the current cross-sectional study, we investigated postural sway in patients with early PD, measured by wearable accelerometers, to test the hypothesis that the postural control system was affected already at a early stage of PD. Moreover, we identified cases of dysfunction of stereopsis in PD patients, and evaluated the relationship between stereopsis and sway parameters.MethodsWe examined23patients with early PD and23healthy, sex-and age-matched control subjects. Postural sway was measured with an accelerometer at the centre of mass at the lower spine. Subjects were asked to stand quietly for30seconds under two usual conditions (eyes open and eyes closed) and two dual tasks conditions (eyes open with dual task, eyes closed with dual task). Stereopsis was assessed using the Titmus fly test.ResultsFive (21.7%) subjects among the control group and14patients (60.9%) among the RBD group showed abnormal stereopsis results. Relative to controls, PD patients showed decreased stereopsis function on the Titmus fly test,In the usual conditions (EO and EC conditions), no differences were found between the control group and PD group. With increasing task difficulty, PD patients showed an increase of RMS values in total RMS, RMS(AP) and RMS(ML) of sway acceleration, compared to control subjects. These differences reached significance during cognitive task performance (EODT, ECDT). PD patients showed larger JERK values with increasing difficulty of the sway task which also reached significance during cognitive task performance.No significant correlation was found between acceleration parameters and UPDRS III Motor Summary Score. And, there were no statistically significant correlations between log seconds of arc of the Titmus test and JERK, even during cognitive task performance.ConclusionThis study suggests that the balance of patients with PD may deteriorate when their attention is diverted or reduced because of attempting to perform cognitive tasks. This finding has some important implications for the strategies to be used in reducing the risk of fall in PD. In addition, deficits of stereopsis are common in early PD patients. Stereopsis was not associated with postural control. Part2Postural sway in idiopathic rapid eye movement sleep behavior disorder:a potential marker of prodromal Parkinson’s disease Background and ObjectiveIdiopathic rapid eye movement (REM) sleep behavior disorder (RBD) is characterized by loss of the normal atonia of REM sleep. Affected patients have excessive motor activity such as punching, kicking, or crying out in association with dream content. Longitudinal studies estimate that over50%of patients with idiopathic REM sleep behavior disorder will develop neurodegenerative parkinsonism (almost exclusively Parkinson’s disease, multiple system atrophy or dementia with Lewy bodies) with a mean latency from REM sleep behavior disorder onset to disease diagnosis of13years. This high conversion rate to neurodegenerative disease provides a unique opportunity to observe directly the development of clinical parkinsonism.PD is thought to have a long prodromal phase. Powerful compensatory mechanisms may mask these clinical symptoms and make them difficult to identify and evaluate in the earliest stages of the illness. Years before PD can be diagnosed clinically, motor signs such as slowing of fine hand movements, reduced arm swing, changes in walking patterns, stiffness, tremor, and imbalance may be detected. A recent study found altered gait parameters in LRRK2G2019S mutation carriers without a clinical diagnosis of PD. This mutation leads to a Parkinsonian syndrome with relatively high probability. In a longitudinal study of idiopathic RBD patients, among the subjects developing clinically overt PD, abnormal Unified PD Rating Scale (UPDRS) motor scores were observed4.5years before the diagnosis could be made, whereas impaired motor performance was detected6-9years before diagnosis using the Purdue Pegboard, alternate-tap and timed up-and-go test. Since many patients with idiopathic RBD are at risk of developing PD, we hypothesized that sway parameters may be changed in patients with idiopathic RBD, even in those who were free of parkinsonism.Stereopsis, or binocular depth perception, depends on the disparity between the views perceived by each eye. The two images are fused in the cerebral cortex and experienced as a single three-dimensional representation under normal circumstances. A recent study found deficits of stereopsis are common in drug-naive Parkinson’s disease patients and associated with nondominant extrastriate cortical atrophy, we hypothesized that dysfunction of stereopsis was also in idiopathic RBD.In the current study, we investigated postural sway in patients with idiopathic RBD, measured by wearable accelerometers, to test the hypothesis that the postural control system was affected already at a prodromal stage of PD. Moreover, we identified cases of dysfunction of stereopsis in RBD patients, and evaluated the relationship between stereopsis and sway parameters.Methods:We examined24patients with polysomnography-confirrned RBD and23healthy, sex-and age-matched control subjects. Postural sway was measured with an accelerometer at the centre of mass at the lower spine. Subjects were asked to stand quietly for30seconds under two usual conditions (eyes open and eyes closed) and three challenging conditions (eyes open with dual task, eyes closed with dual task, and tandem standing). Stereopsis was assessed using the Titmus fly test.ResultsFive (21.7%) subjects among the control group and13patients (54.2%) among the RBD group showed abnormal stereopsis results. Relative to controls, RBD patients showed decreased stereopsis function on the Titmus fly test.The sway parameters of the subjects are shown in Table2and Fig.1. In the usual conditions (EO and EC conditions), no differences were found between the control group and RBD group. With increasing task difficulty, RBD patients showed an increase of RMS values in total RMS, RMS(AP) and RMS(ML) of sway acceleration, compared to control subjects. These differences reached significance in the challenging conditions (EODT, ECDT, and TEO conditions), except for RMS(ML) in the EODT and ECDT conditions. RBD patients showed larger JERK values with increasing difficulty of the sway task which also reached significance in the challenging condition, except for JERK(ML) in the EODT condition.Within the RBD group, but not the control group, there were statistically significant correlations between log seconds of arc of the Titmus test and JERK in the challenging conditions (Fig.2). Furthermore, the RBD patients were divided into RBD patients with normal stereopsis (RBDNrS, n=11) and with abnormal stereopsis (RBDAbS, n=13), in which age and gender were matched, and differences in sway parameters were examined. In the challenging conditions, there were significant differences in JERK values between the RBDNrS group and RBDAbS group, and RBD patients with abnormal stereopsis showed an increase of JERK values compared to those with normal stereopsis. ConclusionThis preliminary finding provides the evidence of the possibility of detecting postural sway changes in patients with idiopathic RBD. Idiopathic RBD patients, especially with abnormal stereopsis, have subtle signs of a balance deficit under challenging stance condition, e.g. with cognitive dual task or tandem standing. The findings also support the intriguing possibility that balance dynamics during challenging conditions may serve as a new, sensitive biological marker of prodromal PD.