Autocorrelated Rhythmic Auditory Stimulations as the Best Way to Use a Metronome for Parkinson's Disease Patients: a Prospective Cohort Study

BACKGROUND

Basal Ganglia dysfunction in Parkinson's Disease (PD) induces gait impairment such as shorter stride length, reduced gait speed, reduced arm swing and an increased randomness in stride duration variability of gait cycles. This increased randomness in gait variability is a typical symptom which can lead to falls, autonomy loss and reduced quality of life. Recently, the Long-Range Autocorrelations (LRA) assessment allowed to emphasize the deterioration of the temporal organization of PD patients' gait variability and demonstrated correlations with disease severity and balance status. These LRA involve a long-memory process which means that every stride depends on the duration of the previous near and far strides. Gait variability should be balanced and should stay in an optimal framework between randomness and over-regularity. This means that LRA should be balanced to keep the healthy adaptive capabilities of the system, to be in the "Optimal Movement Variability" which allows the person to move in a stable but still adaptive way. LRA measurement would therefore be the first quantitative biomarker of gait instability and risk of falling, which is of particular clinical interest.

It is now well known that PD patients have a greater gait variability with a decrease of the LRA. That means that PD patients are more likely to fall which lowers the quality of life. It is also well known that gait disorders do not respond well to dopaminergic pharmacological treatments. Therefore, it seems important to develop non-pharmacological treatments to improve LRA. Rhythmic Auditory Stimulation (RAS), by mean of a metronome, has been studied for years to improve PD patients' gait. Authors showed that the use of a fixed-tempo isochronic RAS reduced the stride duration variability, acting like an external rhythm generator and bypassing the basal ganglia that act like an impaired internal rhythm generator in PD patients. It is then suggested that a broader use of a isochronic RAS, by the mean of a metronome, should be beneficial in gait rehabilitation for PD patients' gait parameters, such as gait speed, stride length, stride duration variability and quality of life.

However, it has been demonstrated that the use of a isochronic RAS decreases LRA in healthy persons and also PD patient. Authors suggested that the cognitive load required by a isochronic RAS would be too elevated for PD patients, creating a dual tasking and diminishing its applicability in a cueing device. This RAS would compel patients to a stereotyped gait instead of an adaptive autocorrelated gait. Then the question is: Should clinicians continue to use an isochronic RAS by the mean of a metronome for PD patients' gait rehabilitation ? Or should clinicians use autocorrelated RAS to avoid loss of adaptivity but still get the beneficial effects of the metronome ? The objective of this study was to analyze the effects of 3 different RAS (isochronic metronome, autocorrelated metronome and random metronome) on PD patients' gait parameters and stride duration variability (magnitude and temporal organization).

METHODS