The effects of dopaminergic medication and task load on trembling and akinetic freezing of gait in Parkinson’s disease

Background In people with Parkinson's disease (PD), freezing of gait (FOG) can manifest as an absence of leg movement (akinetic) or a presence of high-frequency leg trembling. FOG is triggered most often during turning or dual-tasking when OFF-medication, but it is unclear whether the same holds true for akinetic and trembling FOG. Objectives To investigate the effects of dopaminergic medication and cognitive and motor tasks on trembling and akinetic FOG. Method Sixty-three PD patients with daily FOG performed a home-based FOG-provoking protocol OFF and ON-dopaminergic medication. FOG was video-annotated based on pre-specified definitions. We compared the % time in trembling and in akinetic FOG between OFF and ON. We also analyzed these outcomes during various motor tasks and with- and without a cognitive dual task. To identify subgroups, an exploratory k-means cluster analysis was performed. Results Trembling and akinetic FOG co-occurred in most patients (82.5%), although trembling was observed most frequently. Both manifestations were ameliorated by medication, but we identified four different patterns: a responsive mild group (n = 32), an unresponsive akinetic-dominant group (n = 8), and two trembling-dominant groups with (n = 12) and without (n = 11) a response to medication. Task load also affected the manifestations differentially, as dual-tasking and gait initiation induced more akinetic FOG compared to other conditions. Conclusions Trembling and akinetic FOG respond similarly to dopaminergic medication (except for a specific trembling subgroup), yet they are differentially influenced by FOG triggers. Altogether, we suggest that "trembling" may represent a milder form of FOG, although "trembling" as a distinct FOG-variant cannot be rule out.