Objective: To determine the inter-rater and test-retest reliability of the Ziegler test to measure freezing of gait (FOG) severity in people with Parkinson’s disease (PwPD). Secondary aims were to determine test validity, explore test duration as a proxy FOG severity measure, and evaluate test usability.

Background: Current tools to measure FOG severity are largely inadequate for use in clinical settings. Self-report questionnaires may not be sufficiently responsive to detect changes in FOG, and use of video annotations or wearable sensors to measure FOG are resource intensive. The Ziegler test may be suitable for quantifying FOG in clinical practice, but its clinical utility remains unknown.

Method: Twenty-four physical therapists (PTs) watched 36 videos of PwPD and FOG perform the Ziegler test and rated FOG severity via video analyses in real-time using the Ziegler rating scale. Two of these PTs rated an additional 12 videos and repeated the ratings at least one week later. All PTs also completed a test usability survey after the ratings. Inter-rater and test-retest reliability were calculated using intra-class correlation coefficients (ICCs). Correlations between the Ziegler scores, duration, and percentage of time frozen (based on expert video annotations) were determined using Pearson’s r.

Results: The Ziegler test showed good inter-rater reliability (Table 1) and excellent test-retest reliability (Table 2). There were little differences in reliability when considering therapists’ level of experience. The Ziegler test was a valid FOG severity measure, with a high correlation (r=0.72) between the scores and percentage of time frozen. Test duration was moderately correlated (r=0.67) to percentage of time frozen and may be considered as a proxy FOG severity measure. Overall, the PTs found the Ziegler test easy to use but several PTs reported it was difficult to interpret test instructions, identify the presence or type of FOG, and felt the scores were likely underestimating FOG severity in people with worse FOG.

Conclusion: The Ziegler test is a reliable and valid tool to measure FOG when used by PTs in real-time. Test duration may be used as a proxy for FOG severity. A more detailed rating scale that clarifies test instructions and accounts for frequency and duration of FOG episodes may improve its clinical utility.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-reliability-and-validity-of-the-ziegler-test-for-measuring-freezing-of-gait-in-people-with-parkinsons-disease/