Abstract
Background: There have been several pathologic data that support an association between postural instability (PI) and autonomic dysfunction in Parkinson’s disease (PD). The purpose of this study was to investigate the correlation of PI and autonomic deficits in early PD. Methods: We collected 17 patients with a diagnosis of early PD. PI was assessed by computerized dynamic posturography (CDP). Standardized autonomic function test (AFT) and time and frequency domain spectral analysis of heart rate variability (HRV) were performed. CDP data obtained from the 21 patients were compared to that from age- and sex-matched healthy controls. We collected HRV data from 18 other age- and sex-matched controls. All patients were evaluated in the “OFF” state. We used Mann–Whitney U-test to compare parameters of CDP between the early PD and control groups. Spearman correlation was used for correlation analysis between parameters of CDP and autonomic function test in PD patients. Results: Most patients (76.5%) showed mild or moderate autonomic dysfunction in the standardized AFT. In CDP, sensory ratios of equilibrium score (e.g., visual and vestibular) and composite scores were significantly lower in PD patients than in controls. In HRV, the low-frequency/high-frequency ratio during the tilt and the gap of low- frequency/high-frequency ratio from supine to tilt were significantly different in both groups. The parameters of time and frequency domains of HRV reflecting parasympathetic function were correlated with equilibrium scores for somatosensory organization test in CDP. Discussion: PI was associated with parasympathetic autonomic dysfunction in early PD. This result was in accordance with a previous assumption that PI in PD is related to parasympathetic cholinergic neuron loss in the brainstem.
Highlights
Postural instability is one of the cardinal motor symptoms in Parkinson’s disease (PD), especially in the late stage
This result is in accordance with previous studies that postural instability in PD is associated with brainstem parasympathetic cholinergic neuronal loss [25,26]
Our key finding on a significant correlation between the sensory ratios of equilibrium score such as somatosensory, vestibular, visual preference, and composite score for sensory organization test (SOT), and parasympathetic autonomic abnormality as estimated with heart rate variability (HRV) supports the hypothesis that the parasympathetic cholinergic system in the brainstem such as dorsal glossopharyngeus–vagus complex and pedunculopontine nucleus (PPN) may be responsible for postural control in PD [27,28]
Summary
Postural instability is one of the cardinal motor symptoms in Parkinson’s disease (PD), especially in the late stage. According to previous studies [1,2,3,4,5,6,7], patients with early PD who showed a normal result at the pull test in the bedside examination revealed a mild postural instability in both static and dynamic posturography. We performed this study to investigate the correlation of postural instability assessed with computerized dynamic posturography (CDP) and autonomic deficits assessed with various autonomic function tests in patients with early PD. Because the degree of autonomic dysfunction in early PD estimated with a battery of standardized autonomic function test is known to be mild [17], we added time and frequency domains spectral analysis of heart rate variability (HRV), a powerful and reliable tool for assessing the fluctuations in the autonomic nervous system and balance of sympathetic and parasympathetic activities [18,19]. This result was in accordance with a previous assumption that PI in PD is related to parasympathetic cholinergic neuron loss in the brainstem
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