Parkinson’s Disease: Managing Freezing of Gait

FOG is a common symptom in PD and a major cause of falls. It is characterised by an episodic and disturbing gait disorder in parkinsonian patients characterised by the inability to initiate or continue locomotion. When a patient attempts to lift a foot to step forward, the foot is felt to be ‘stuck’ to the ground, sometimes with trembling of the legs. FOG occurs in 53% of PD patients who are in advanced stages of disease but can occur even in early stages. The freezing episodes usually last a few seconds to a minute, though longer durations are not uncommon. In general, freezers have difficulty in walking horizontally, but vertical leg movements such as climbing of stairs are preserved.

Whilst pharmacological treatment can be partially effective in reducing FOG, auditory or visual cues have been shown to be beneficial in triggering an individual’s ability to take a step. FOG can be broadly separated into three main groups: Dopaminergic sensitive, dopaminergic resistant and dopaminergic drug provoked. The first group, dopaminergic sensitive, can be alleviated by L-dopa, however, this can similarly lead to FOG during OFF-periods, where the effects of the drug treatment is wearing off. As such, there appears to be a significant interaction between medication state and manifestation of FOG, in terms of quantity of events and types of freezing. ON medication-FOG is not only less frequent but also characterised by a higher prevalence of leg trembling and small shuffling steps, or festination, and a reduced prevalence of akinesia compared to OFF medication-FOG. The events which elicited the highest prevalence of FOG-episodes have been identified as gait initiation and turning.

The underlying pathophysiology of FOG is not fully understood. Due to diversity in presentation of FOG, it is likely to involve diverse neural circuitry in addition to the characteristic loss of dopaminergic cells in the substantia nigra pars compacta. Structural changes as evidenced in neuropathological and imaging studies have associated FOG with various other regions in the brain, including grey matter areas such as visuospatial, thalamic regions, and areas involved in executive function, as well as various white matter tracts.

How FOG is dealt with currently

Drugs

FOG is a notoriously difficult problem to manage pharmacologically. The current drug therapies involve L-dopa, the gold standard for Parkinson’s Disease, and MAO-B inhibitors such as rasigiline or segeline. There are also other drugs for FOG, such as amantidine and methylphenidate, however, their clinical efficacy is limited, with varying effects depending on the form of FOG in question. These challenges with drugs have led clinicians to seek adjunctive treatment methods such as sensory cueing.

Cueing

It has been shown that attention processing, necessary during performance of a dual task, negatively affects gait. Deficits in executive function, including attention, are common in PD, and reduced basal ganglial activation further appears to be responsible for failure of gait initiation. Some non-pharmacological interventions involving sensory tricks and cues have therefore been developed to circumvent the problems by providing an external trigger to initiate movement. An example of such intervention is the use of visual cues on a walking surface, e.g. stationary lines placed at fixed distances, or laser lines projected onto the floor. These allow users to take steps guided by the external cue. The external cue activates the motor cortex, which remains intact, rather than the basal ganglia, or the supplementary motor area circuit which has become impaired.

In a review by Nieuwboer looking at a range of cueing methods, no impact was seen on gait initiation using auditory cues. Visual cues on the other hand, significantly improved movement amplitudes in both people with and without FOG. One specific study in the review, found that when turning, freezers were able to produce large turning arcs when using a cue, unlike non-freezers and controls. Another study completed by Dietz et al., saw a reduced number of FOG episodes when using cues that form parallel lines during a gait course with turns and doorways. In a separate review by Rocha et al., the use of cues led to an improvement in step length, cadence and stride length. Visual cues in particular, were useful in improve speed, cadence and step length. These promising findings in visual cueing have led us to develop a low cost, simple solution that promises to have significant improvements to the quality of life of patients.

Path Finder

Path Finder is a laser light cueing device which attaches to a shoe. It projects a green laser line in front of the opposing foot. The cueing is constant for every step, which removes the need for the user to activate the light during FOG. The device has been tested with local PD support groups, and has had positive feedback from users, with reports of “increased confidence” and improved ability to navigate hazards in environments in which they are prone to freezing.

An interesting phenomena described in the research has been the advantages of continuing versus on-demand cueing. In analysis by Velik et al. it was found that the duration of freezing episodes was reduced by 51% in continuous cueing and by 69% using “on-demand” cueing, however, the actual number of freezing episodes were reduced by 43% when using continuous cueing and by 9% when using “on-demand” cueing.16 This highlights the ability for continuous cueing, a feature of the Path Finder, to prevent freezing from occurring in the first place. However, Path Finder provides cues only when the opposite foot is in contact with the floor, and hence it may have further benefit from the ‘true’ continuous cues. It is thought that the intermittent cue may act better in reducing the time spent in FOG, due to it bringing more attention to the act of gait. Reducing the number of freezing episodes is particularly important to reduce the risk of falling, which is the highest during the first few seconds of a freezing episode.

External cues are thought to work by reducing the need to internally plan and prepare movements, taking on an executive role and decreasing cognitive load. Further, it may act to focus attention during the performance of what is considered a set of complex tasks and hence aid in gait prioritisation. The fact that visual cues were found to improve movement amplitudes in people with and without FOG, strongly suggests that Path Finder may be able to assist people with PD in a broader sense than only when they experience freezing.