This study provides temporal-spatial gait data for people with PSP and compares their gait with PD and HOA. Preferred speed walks showed decreased nSL to be the main contributor to slowed walking speed in both PD and PSP. PSP also had lower cadence than ‘normal’ at preferred speed. People with PSP had reduced nSL for their cadences across all the self-selected speeds (reduced intercept) indicating an alteration in the gain of the normal stride length - cadence relationship.
Comparison of ‘walks’ at similar stride length showed that people with PSP have significantly higher cadences for the stride length than HOA and more ‘abnormal’ DS% and step width than PD. The significantly increased DS% and step width may be manifestations of unsteadiness or compensations to enhance postural stability
]. Falls are a cardinal feature of PSP and the occurrence of falls has been linked to the presence of gaze problems, axial rigidity, cognitive decline
]. Increased DS% and step width may be an indication that dynamic instability is also a contributing factor to fall frequency in PSP. However, as DS% was also significantly greater for the PD group when compared with HOA, the finding may be a result of greater overall severity of gait abnormality, despite no difference in disease duration, among the PSP group than for PD, rather than an additional gait abnormality. This is consistent with the clinical finding of more rapid disease progression for people with PSP.
There are features of PSP that are likely to contribute to gait abnormalities. Motor causes include weakness and spasticity, which along with bradykinesia is thought to explain the ‘lurching’ style gait
]. Axial (more so than appendicular) rigidity and dystonia are often present. The visual problems including vertical movement and convergence difficulties, reduced blinking and involuntary eyelid closing, may also lead to gait alterations as well as directly contributing to fall frequency
]. Finally, many of the cognitive problems that are features of PSP may contribute to gait instability, including apathy and decline of executive function, reduced processing speed, impaired attention, and diminished working memory.
Callisaya et al.
] found that the speed of the walk explained most of the variation in the temporal variability found among older people. This, they presume, is because walking at slower speeds disrupts the temporal automaticity of gait. In this study, we controlled for speed by selecting a self-paced walk at a target stride length. The selected walk was a slow or very slow walk for all the HOA, but was a fast or very fast walk for most (84%) of the PSP. All participants may have been influenced by the effect of non-preferred speed on variability, however stance time variability for all groups in this study were comparable to that reported for older adults, mean 0.02s (SD 0.01)
This study showed that while the stride length versus cadence relationship was intact in our PSP participants, it had a lower intercept, that is, a smaller stride length was associated with a higher cadence. This was also characteristic of the PD group in this and previous studies
], although the lower intercept in our PSP group was more severe. This suggests that people with PSP share the defective scaling of stride length that underlies gait disturbance in PD, but to a more severe extent. These findings are consistent with the concept of a mismatch in stride length selection associated with basal ganglia malfunction in both disease states. Given the upper brain stem involvement in PSP we might have expected some additional disturbance of cadence control
]. While the PSP group had lower cadence at preferred speed and higher cadence when walks with similar stride lengths were compared, no disruption to the linkage between stride length and cadence manifest in the SLCrel. This may be expected to break down with progressive involvement of the lower brain stem, and may be present in the PSP patients who did not satisfy inclusion criteria for the present study.
The findings from this study indicate that some treatment modalities that are successful in improving function for people with PD, such as the use of cueing when walking to maintain stride length, may also be appropriate for people with PSP. However, the instability-related gait abnormalities found in this PSP group support the inclusion of additional treatment techniques to optimize their gait and maintain independent functioning for as long as possible.
The study findings need to be considered in the context of several methodological limitations. There were differences in the groups which may have an impact on the data and the conclusions that can be drawn. While disease duration was similar, it was not possible to directly compare disease severity between the two patient groups as two different scales were used. Differences in disease severity may explain some of the differences in gait between the patient groups.
The difficulty in recruiting participants with PSP who meet the inclusion/exclusion criteria for this study has resulted in low participant numbers. The testing was carried out without withholding of levodopa medication. All PD participants and half of the PSP participants were prescribed levodopa medication. Levodopa medication is known to normalize stride length and the stride length versus cadence relationship intercept for people with PD
]. It is not known whether it achieves a similar effect on gait in PSP and some of the gait abnormalities may be underrated particularly among the PD group. While this may be seen as a limitation, the data reflects the presentation of gait abnormalities seen in clinical settings. Given that gait within patients with advanced PD fluctuates extensively and often does not follow a predictable pattern related to medication timing
], and the clinical presentation among our small cohort of PSP patients was considerably heterogeneous, we were not able to carry out a comparison of gait between the PSP patients prescribed versus not prescribed levodopa medication. However, we recommend such a study for future research.
That there were more females in the HOA group may have impacted on the results. Gender differences are most apparent for the variables of speed and stride length where females have lower speed and shorter stride length than males
]. That we never-the-less found significant differences between the groups in these two variables indicates that the group gender differences are unlikely to have impacted on our conclusions. Weight was previously not found to be associated with similar gait variables in a population based study of older people