Time To Navigate (TTN): A practical objective clinical measure for freezing of gait severity in people with Parkinson’s disease

Abstract

Abstract Objectives Existing objective assessments for freezing of gait (FOG) severity may be unwieldy for routine clinical practice. To provide an easy-to-use clinical measure, this cross-sectional study explored if time to complete the recently-validated FOG Severity Tool (or its components) could be used to reflect FOG severity. Methods People with Parkinson’s disease who could independently ambulate eight-metres, understand instructions, and without co-morbidities severely affecting gait were consecutively recruited from outpatient clinics. Participants were assessed with the FOG Severity Tool in a test-retest design, with time taken for each component recorded using a stopwatch during video-analysis. Validity of total FOG Severity Tool time, time taken to complete its turning and narrow-space components (i.e., Time To Navigate, TTN), and an adjusted-TTN were examined through correlations with the FOG Questionnaire, percentage of time spent with FOG, and FOG Severity Tool-Revised score. To facilitate clinical interpretation, TTN cutoff was determined using scatterplot smoothing (LOESS) regression whilst minimal important change (MIC) was calculated using predictive modelling. Results Thirty-five participants were included [82.9%(n=29)male; Median(IQR): age – 73.0(11.0)years; disease duration – 4.0(4.5)years]. The FOG Severity Tool time, TTN, and adjusted-TTN similarly demonstrated moderate correlations with the FOG Questionnaire and percentage-FOG, and very-high correlations with FOG Severity Tool-Revised. TTN was nonlinearly related to FOG severity such that a positive relationship was observed in the first 300-seconds, beyond which the association plateaued. MIC for TTN was 15.4-seconds reduction in timing (95%CI 3.2 to 28.7). Conclusions The TTN is a feasible, interpretable, and valid test of FOG severity, demonstrating strong convergent validity with the FOG Severity Tool-Revised. In busy clinical settings, TTN provides a viable alternative when use of existing objective FOG measures is (often) unfeasible. Impact statement Busy clinicians need easy-to-use measures. In under 300-seconds, TTN test offers this for FOG severity, with a 15.4-seconds decrease in TTN time considered minimal improvement.