Speech Outcomes in Anodic Deep Brain Stimulation for Parkinson's Disease

This is a prospective, randomised, double-blinded, cross-over deep brain stimulation (DBS) programming trial involving participants with Parkinson’s disease implanted with a DBS system at least 4 months prior. After meeting inclusion criteria, enrolled participants will be randomised into one of the study arms below. They will be programmed with the pre-set programming protocol (described below) by a single unblinded DBS neurologist, using the Boston Scientific Vercise implantable generator. Participants will be randomised into one of two study arms and remain blinded throughout the duration of the study: - Arm 1: Participants will be initially programmed with an anodic program and cross-over to an optimised cathodic program after 10 days. They will remain on this program for a further 10 days. - Arm 2: Participants will be initially programmed with an optimised cathodic program and cross-over to an anodic program after 10 days. They will remain on this program for a further 10 days. Anodic programming protocol: Optimisation of current (increase or decrease) is permitted to allow for achieving the best on-state while limiting side effects. No change to contact location is permitted. Higher frequency settings are permitted in the instance of refractory tremor or should a patient prove difficult to sustain in the on-state. No change to pulse width is permitted. Optimised cathodic programming protocol: In addition to what is permitted for anodic programming, any change to frequency (increase or decrease) is permitted. This study intends to enrol 30 participants in total (15 for Arm 1 and 15 for Arm 2). Study personnel assessing the outcomes and analysing the results will be blinded to program settings. Randomisation will follow a block-design to ensure equal numbers of participants in each arm. Double-blinded assessments will be performed at baseline, day 10 and day 20. Participants will be assessed in an off-medication, on-stimulation state at a research facility with specific requirements for the following assessments: 1. Appendicular motor state assessment will occur in an anechoic clinical room with low ambient noise. This includes Parkinson’s disease motor and dexterity assessments (MDS-UPDRS III & 9-hole peg test), along with patient questionnaires. Assessments will be administered by the single unblinded DBS neurologist with separate scoring of assessments performed by blinded raters. 2. Speech assessment will occur in the same anechoic clinical room with low ambient noise, with a head-worn microphone placed at a fixed distance from the participant’s lips. Participants will perform standardised speech tasks. Speech tasks are recorded and subsequent acoustic analyses will be performed by blinded researchers. 3. Gait and balance assessment will then immediately occur in the adjacent physiotherapy lab with large open spaces. Participants will perform standardised gait and balance tasks while wearing inertial measurement units. The tasks will be administered by physiotherapists, blinded to the intervention. Gait and balance performance is recorded and subsequent analyses will be performed be blinded researchers. Specific timing of intervention: - After all three assessments, the DBS neurologist will deliver the intervention to the blinded participant by programming them based on the pre-set programming protocol, according to their randomised arm. This will occur over approximately a one-hour period, with the participant subsequently leaving the research facility and returning to their normal activities at home. - After a wash-in/wash-out period of 10 days (+/- 3 days to allow for scheduling) the patient will return for a repeat set of assessments in the above order. Similarly, at the end of all three assessments, the next programming intervention (crossover) occurs. - At each programming session, the DBS neurologist is able to monitor for adherence to the particular program through the clinician programmer and patient history, including documenting minor self-adjustments in amplitude made by each participant, if required. Study exit: Prior to study exit and unblinding, the participants’ impression of blinding will be assessed. Participants will exit the study after the final assessment at day 20 and have the option of choosing to remain on either program after unblinding.