Modeling freezing of gait in Parkinson's disease with a virtual reality paradigm.

Freezing of gait is a paroxysmal and disabling symptom that commonly affects patients in the latter stages of Parkinson's disease, however the intermittent nature of this symptom makes it difficult to study in the clinical setting. Our research group has previously reported a correlation between self-reported freezing of gait symptoms and performance on a seated virtual reality gait task. In this study, we sought to determine whether behavioral measures recorded on this task were correlated with actual clinical measures of freezing of gait recorded in a cohort of 38 Parkinson's disease patients whilst in their clinically defined 'off' state. Firstly, patients with freezing of gait had a significantly larger frequency of spontaneous motor arrests recorded on the virtual reality gait task than 'non-freezers'. In addition, in those 24 patients with clinically proven freezing of gait, the number and percentage of time spent with freezing on the virtual reality task were both moderately correlated with the duration of freezing of gait recorded on the timed up-and-go tasks. These findings suggest that the freezing behavior observed during a virtual reality gait task may share similar neural substrates to freezing of gait. Such a relationship could offer a potential avenue for modeling the phenomenon of freezing of gait in Parkinson's disease, allowing for the exploration of the neural correlates of freezing.

Assessing the utility of Freezing of Gait Questionnaires in Parkinson's Disease.

There are currently two validated questionnaires, the Freezing of Gait Questionnaire and the New Freezing of Gait Questionnaire, that are intended to assess the degree of freezing of gait in patients with Parkinson's disease. However, to date no study has attempted to determine whether ratings on these questionnaires accurately reflect the severity (frequency and duration) of actual freezing episodes experienced by patients. We studied twenty-four patients with Parkinson's disease who self-reported significant freezing while in their practically-defined 'off' state. Prior to clinical assessment they completed both freezing of gait questionnaires before being video-recorded while performing a series of timed up-and-go tasks, which incorporated turning, rotating and passing through narrow gaps. The rating of video recordings by two independent observers identified a total of 530 freezing events. The frequency and duration of freezing episodes for each patient were calculated and correlated with questionnaire ratings. Scores on either questionnaire did not correlate with either the frequency or duration of freezing episodes experienced by patients during objective assessment. These results suggest the need to re-evaluate the utility of questionnaires in the assessment of freezing of gait. Furthermore, these results highlight the need for accurate objective methods of identifying freezing events when assessing future clinical interventions aimed at reducing this potentially disabling symptom of Parkinson's disease.