Validity and reliability of a new clinician-rated tool for freezing of gait severity

Purpose: The Freezing of Gait Severity Tool (FOG Tool) was developed because of limitations in existing assessments. This cross-sectional study investigated its validity and reliability. Methods: People with Parkinson’s disease (PD) were recruited consecutively from clinics. Those who could not walk eight-metres independently (with or without an assistive device), comprehend instructions, or with co-morbidities affecting walking were excluded. Participants completed a set of assessments including the FOG Tool, Timed Up and Go (TUG), and Freezing of Gait Questionnaire. The FOG Tool was repeated and those reporting no medication state change evaluated for test-retest reliability. Validity and reliability were investigated through Spearman’s correlations and ICC (two-way, random). McNemar’s test was applied to compare the FOG Tool and TUG on the proportion of people with freezing. Results: Thirty-nine participants were recruited [79.5%(n=31) male; Median(IQR): age–73.0(9.0) years; disease duration–4.0(5.8) years]. Fifteen (38.5%) contributed to test-retest reliability analyses. The FOG Tool demonstrated strongest associations with the Freezing of Gait Questionnaire (ρ=0.67, 95%CI 0.43–0.83). Test-retest reliability was excellent (ICC = 0.96, 95%CI 0.88–0.99). The FOG Tool had 6.2 times the odds (95%CI 2.4–20.4, p<0.001) of triggering freezing compared to the TUG. Conclusions: The FOG Tool appeared adequately valid and reliable in this small sample of people with PD. It was more successful in triggering freezing than the TUG.