The static stabilometry patterns associated with Parkinson's disease (PD, n = 15) and spinocerebellar ataxia (SCA, n = 15) were compared with those of normal control (n = 15) by measuring the fractal dimensions. Fractal dimensions were estimated using the modified pixel dilation (mPD) method. The fractal dimensions with closed eyes showed a significant correlation with Environmental area for SCA group (p
Keywords: Fractal dimension; static stabilometry; Parkinson's disease; spinocerebellar ataxia
Parkinson's disease (PD) and spinocerebellar ataxia (SCA) are neurodegenerative diseases of later life. A clinical hallmark of advanced PD and SCA is postural instability, which results in significant morbidity due to falls, associated injury and functional impairment1. To evaluate the postural dyscontrol, we measured fractal dimension of stabilometry pattern. Fractal dimension is a geometry advocated by Mandelbrot2, which was established as a method expressing an image of self-similarity. The value of the fractal dimension reflects the complexity of the image, the higher being the more complex. The usefulness of the fractal dimension has been reported in analysis of the sulcus in the brain 3, electroencephalograms4, bacterial colonies5, neurons 6,7, and heart rate8-10.
In this study, we utilized fractal dimension analysis to yield useful parameter to evaluate the postural dyscontrol associated with PD and SCA.
PATIENTS AND METHODS
The PD group consisted of 15 patients (7 males and 8 females) with a mean age of 65.0 +/- 10.0 (mean +/- SD) years. The disease duration was 2.9 +/- 2.4 years. PD patients were divided into three groups according to Hoehn-Yahr stage (Table 1). The SCA group consisted of 15 patients (8 males and 7 females) with a mean age of 59.5 +/- 11.9 years. The disease duration was 4.5 +/- 3.2 years. SCA patients could be divided into three groups according to the SCA disability grade of Japan national research group of ataxic disorders11 (Table 2).
A group of normal controls, 8 males and 7 females, mean age 59.5 +/- 10.5 years, without a history of head injury or physical or neurological illness, were also tested. Informed consent was obtained from all patients and control subjects prior to testing.
Each subject assumed a relaxed standing posture in bare feet, with feet shoulder-width apart and arms folded across the chest, on a force platform. Subjects performed for each 60-sec trial with eyes open and closed. Environment and Longitude/Environmental areas were calculated by this system. Environmental area indicates sway area. Longitude/Environmental area indicates sway path per unit sway area.
The traced image was input into the image-analyzer through a television camera, and a fractal dimension of the stabilometry pattern was measured by a modified pixel dilation as described below (see Measurement of the fractal dimension section). When the image was input through the television camera, the stage position was fixed so that the magnifying factor was constant.
Statistical analysis was carried out using means and SDs, analysis of variance (ANOVA) and Student's t-test. Statistical significance was defined as p
The fractal dimensions with closed eyes showed no significant correlation with the parameter of Environmental area for normal and PD group (correlation coefficient r=0.055, 0.109, respectively), and significant correlation with that for SCA group (Figure 3A, r=0.730, p
As shown in Figure 3, the fractal dimensions were 1.61 +/- 0.04 (mean +/- SD) and 1.63 +/- 0.04 with open or closed eyes, respectively, for the normal group. Those were 1.63 +/- 0.05 and 1.66 +/- 0.04 for PD group, and 1.63 +/- 0.06 and 1.69 +/- 0.06 for SCA group. The fractal dimension for SCA group was significantly higher with closed eyes than that with open eyes (Figure 4, SCA, p
In contrast, no significant correlation was found between Environmental (Figure 5A,B) and Longitude/ Environmental (Figure 6A,B) areas, and the clinical stages for PD and SCA groups. The fractal dimension with closed eyes was higher when the clinical stage was more severe with PD and SCA group (Figure 7AB). The fractal dimension with closed eyes for Hoehn-Yahr III stage of PD was significantly higher than that for stage I (Figure 7, PD, p
Postural control involves appropriate integration of the visual, vestibular, and somatosensory systems . When this interaction is disrupted, the normal weighing of sensory cues is altered and the remaining cues may alternatively provide adequate information for proper maintenance of balance. These changes can be assessed by static stabilometry 15,16. However, traditional parameters of stabilometer were not well correlated to the severity of diseases, and quantitative analysis of the stabilometry pattern using gravity movements has not been fully investigated. Therefore, we have attempted to estimate the stabilometry pattern more quantitatively by measuring the fractal dimension. A fractal dimension in a two-dimensional picture ranges from 0 to 2, with 0 for the point, 1 for the straight line, and 2 for the plane. This dimension is higher when the picture is more complex (Figure 2). This study examined a possible usefulness of the fractal dimension in an evaluation of postural instability in PD and SCA.
The fractal dimensions with closed eyes showed a significant correlation with parameter of Environmental area for SCA group (Figure 3A, p
The fractal dimension for SCA group was significantly higher with closed eyes than that with open eyes (Figure 4, SCA, p
It is often difficult to determine the clinical stages by means of quantitative scale. In fact, no significant correlation was found between Environmental (Figure SA,B) and Longitude/Environmental (Figure 6A,B) areas, and the clinical stages for PD and SCA groups. However, the fractal dimension with closed eyes showed a good correlation to the clinical stage with PD and SCA (Figure 7A,B). The fractal dimension with closed eyes for Hoehn-Yahr III stage of PD was significantly higher than that for stage I (Figure 7, PD, p
We wish to thank Okayama Kyokuto Hospital for paving the cases.
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Yasuhiro Manabe, Eiichi Honda*, Yoshihiko Shiro, Kenichi Sakai, Ichiro Kohira, Kenichi Kashihara, Toshikiyo Shohmori and Koji Abe
Department of Neurology, Okayama University Medical School, Okayama
*Department of Dental Radiology and Radiation Research, Faculty of Dentistry, Tokyo Medical and Dental University, Tokyo, Japan
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