Freezing in Parkinson's May Be Linked to Perception of Space
By Allison Gandey
Medscape Medical News
October 2, 2009 — Patients with Parkinson's disease and problems with motor freezing may actually be struggling with sensory–perceptual issues, a new study suggests. The findings call into question current thinking that freezing is a motor impairment and propose instead that it is linked to problems with perception of space. The work is published in the Journal of Neurology, Neurosurgery and Psychiatry.
Because freezing frequently occurs in confined spaces, investigators questioned whether sensory–perceptual issues could be at play. They studied 15 patients with Parkinson's disease and freezing episodes, another 16 Parkinson's patients without freezing, and 16 healthy, age-matched control patients.
Researchers studied how doorway size influenced behavior. They evaluated changes in spatiotemporal aspects of gait while walking through 3 different-sized doorways. One was narrow, another normal, and a third wide.
They found that Parkinson's patients experiencing freezing were most affected by the narrow doorway. While approaching the door, these patients took shorter steps, had more gait variability, and tended to widen their base of support. Investigators found that patients with freezing demonstrated increased within-trial variability of step length and step time, which was exaggerated as doorway size decreased [F(4,88) = 2.99; P < .023].
Parkinson's patients with no freezing episodes were also affected by the narrow doorway and tended to widen their base of support.
"Perhaps the most important consideration for clinicians is that sometimes it is important to think outside the box," lead investigator Quincy Almeida, PhD, from Wilfrid Laurier University in Waterloo, Ontario, Canada, told Medscape Neurology. "In the case of the current study's findings, it suggests that when we detect clinical motor impairments, it is important to question what the underlying mechanism for these impairments might be."
Dr. Quincy Almeida
Shorter Steps, Gait Variability, and Wider Base of Support
Dr. Almeida suggests that because his team could identify changes to the normal walking pattern before the door, it is likely that there is a sensory-perceptual mechanism that contributes to — and potentially even causes — the observable freezing episodes identified clinically.
"Probably the most surprising finding is that even Parkinson's patients who do not have issues with freezing can be profoundly influenced by the perception of an upcoming narrow doorway," Dr. Almeida said.
"In other, normal-sized doorways, the typical Parkinson's patient behaves much more like a healthy older adult with no hint of a change in walking pattern prior to the doorway. Yet in the narrow doorway, there is a shift in behavior and the nonfreezer behaves more like a freezer," he said.
Other research teams such as the one led by Jeffrey Hausdorff, PhD, from Tel-Aviv University in Israel, have also observed impaired regulation of stride in Parkinson's patients with freezing (Exp Brain Res. 2003;149:187–194).
In contrast, Erwin Van Wegen, PhD, from the VU University Medical Center in Amsterdam, the Netherlands, found that small spaces in the form of a virtual corridor had no effect on gait in Parkinson's (Parkinsonism Relat Disord. 2006;12:21–27).
More Study Needed
"We are now focusing on trying to identify what it is about the doorway that influences the change in walking pattern," Dr. Alemeida said. "If this can be determined, then the potential to treat or even change doorway designs for freezers would be high."
Dr. Almeida points out that many questions remain as to whether this is a sensory problem in which the eyes inappropriately analyze characteristics of the doorway or whether it is perhaps a cognitive issue and a failure to perceive depth or doorway width.
The researchers point out that patients with Parkinson's appear to be unable to accurately evaluate self-motion in relation to upcoming obstacles. This may be an important perceptual factor to consider for other situations such as entering an elevator or any confined or crowded space.
The investigators suggest that an eye-tracking device might be useful in future research to monitor participant gaze on approach.
This study was supported by the Natural Sciences and Engineering Research Council of Canada. The researchers have disclosed no relevant financial relationships.
J Neurol Neurosurg Psychiatry. Published online September 15, 2009.
