Gait dynamics in Parkinson's disease: relationship to Parkinsonian features, falls and response to levodopa
Introduction
One of the hallmarks of Parkinson's disease (PD) is its effect on gait. Patients with PD often walk with a reduced gait speed, shorter stride length, stooped posture, and reduced arm swing [1], [2], [3], [4], [5]. Control of cadence (more specifically, the average step rate) is generally intact, but some patients may increase the stepping frequency to compensate for a reduced stride length [6]. Gait disturbances may also include gait instability and arrhythmicity, as manifest by increased stride-to-stride variability in walking [7], [8].
Gait disturbances and instability may predispose to falls in PD. Many subjects with PD have a high risk of falling, even compared to age-matched controls. In a community-based sample of 63 patients with PD, Ashburn et al. [9] found that 40% had experienced one or more falls in the previous 12 months. In a 6-month, prospective study, Bloem at al. [10] observed that 51% of PD subjects with moderately advanced disease fell at least once while only 15% of age-matched control subjects fell. Gray and Hildebrand [11] observed that 59% of PD subjects fell during a 3-month period. In a 1-year prospective study, Wood et al. [12] recently reported that 68% of the PD subjects had at least one fall. Falls may lead to injuries, hip fractures, fear of falling, and restriction of activities that in turn contribute to institutionalization, loss of independence and increased mortality [9], [11], [13], [14], [15], [16], [17]. Despite detailed testing of gait and balance in fallers and non-fallers, the specific factors that are critical to falls and fall prediction in PD remain elusive [10], [17].
In other populations, stride-to-stride variability, the inability to regulate gait on a stride-to-stride basis, has been shown to be predictive of future falls. In older adults, for example, increased stride-to-stride variability of the spatial–temporal measures of gait has been associated with future falls in prospective studies [18], [19]. Stride time variability, the magnitude of the fluctuations of the gait cycle duration, was associated with multiple factors including strength, balance, gait speed, functional status, and even mental health. These other measures, however, did not discriminate future fallers from non-fallers [19]. For example, reduced gait speed was related to fear of falling, but not to falls [18]. Similarly, among patients with Alzheimer's disease, stride length variability appeared to be an effective predictor of falling, whereas (average) gait speed and (average) stride length were not [20]. Evidently, stride-to-stride variability is more closely linked to falls than other changes in gait, at least in certain populations. The increased variability of gait may be a manifestation of a decline in motor control and dynamic balance, deficits that apparently heighten the risk of falling.
Little is known about the stride-to-stride regulation of gait dynamics in PD. A few studies have observed increased variability in patients with PD compared to controls, noting that this variability tends to increase with disease severity [7], [8], [21]. However, the relationships between gait variability, fall risk, and other parkinsonian features have not been well studied. The effects of levodopa on falls and gait variability are also largely unknown. To better understand the effects of PD on walking, especially gait instability, and the factors that contribute to gait variability and fall risk in PD, we studied: (1) the relationship between gait variability, fall history and other parkinsonian features; and (2) the effect of levodopa on gait variability, fall frequency, and these relationships in subjects with Parkinson's disease.
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Subjects and protocol
Subjects with idiopathic PD, as defined by the UK Brain Bank criteria [22], were recruited from the outpatient clinic of the Movement Disorders Unit of the Tel Aviv Sourasky Medical Center. Subjects were invited to participate if they were between the ages of 50 and 80 years, were on levodopa treatment, experienced motor response fluctuations, and were able to ambulate independently while in an “off” state (i.e., at least 12 h off anti-parkinsonian medications). Subjects were excluded if their
Subject characteristics
Thirty-two subjects (23 men) were studied. Subjects were 62±7.5 years old. Table 1 summarizes the demographics and clinical characteristics of the study populations. Measures of gait dynamics are summarized in Table 2.
Relationship between gait dynamics and other PD symptoms
In the “off” state, the average stride time was not associated with age, gender, MMSE score, disease duration, any UPDRS measure, any measure of the CAPIT, fall frequency, or stride time variability. In contrast, the stride time variability was significantly associated with fall
Discussion
Previous studies have reported increased stride-to-stride variability among patients with PD [7], [8], [21]. Our results are consistent with these earlier findings. Here, we extend these results in a number of important ways. We demonstrate that the locomotor control system's ability to regulate the stride-to-stride variations in gait timing is especially impaired among PD subjects with a history of falls. We find that fall frequency and stride-to-stride variability are not related to tremor,
Acknowledgements
This work was supported in part by NIH grants AG-14100, RR-13622, HD-39838 and AG-08812. We thank E. Shabtai and D. Comanshter for their assistance with statistical analysis and the subjects for their time and effort.
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