Freezing of Gait in Parkinson's Disease: A Heterogeneous Phenomenon Across Assessment Tools.

Freezing of gait (FOG) is common in Parkinson's disease (PD), yet uncertainty remains regarding the optimal criterion for identifying freezers. Self-reported FOG and performance-based FOG assessments are widely used, but their relative value is unclear. This study compared four different tools for identifying freezing and how these classifications relate to simple functional tests feasible in home or clinical environments. The participants with PD completed four FOG-related assessments (two movement disorder society-unified Parkinson's disease rating scale [MDS-UPDRS] items and two observations during Parkinson's disease functional movement battery [PD-FUNC] items). Based on the outcomes, individuals were classified as freezers (positive on at least two tools), occasional freezers (nonzero score on one indicator), or nonfreezers (zero on all tools). Disease severity was recorded using Hoehn and Yahr (H&Y) staging. Groups were compared using the PD-FUNC test battery, which includes rotation, dexterity, balance, and locomotion tasks. Analyses were adjusted for disease severity. Additionally, a 5-year longitudinal case study illustrated fluctuations in FOG-related and functional performance over time. As expected, freezing was the most prevalent in advanced disease (H&Y Stage 3). However, up to 40% of those classified as freezers were in earlier stages (H&Y Stages 1 and 2). After adjustment for disease severity, only a small subset of PD-FUNC items differentiated groups. Post hoc analysis of these items showed that significant differences were limited to comparisons between freezers and nonfreezers. Freezers required more time to complete a 360° rotation. Unexpectedly, typing speed, a dexterity measure, also differed significantly between freezers and nonfreezers. Occasional freezers showed higher MDS-UPDRS Part III scores compared with nonfreezers, whereas Part II scores displayed a graded increase across groups. The longitudinal case study demonstrated recurrent periods of reported freezing and severe falls that coincided with prolonged rotation times, followed by recovery periods linked with return to physical activity. Combining multiple indicators improves the identification of FOG and reveals that freezing is present even in earlier PD stages. Simple PD-FUNC items, particularly rotation time and typing speed, distinguish freezers from nonfreezers after adjusting for disease severity. The case study highlights that reported freezing may occur in discrete periods, often associated with falls, but recovery is possible and appears related to resumption of physical activity. These findings support the clinical utility of PD-FUNC for monitoring FOG-related functional changes over time.