Identification of Clinically Relevant Markers of Deep Brain Stimulation Electrode Impedance

The study will look into the changes of Deep Brain Stimulation (DBS) measured impedances in patients of Parkinson disease (PD) as a function of their functional state (lying, sitting and walking) and dopaminergic medication intake (levodopa or dopamine agonists). The goal is to use DBS measured impedance as a surrogate of the functional and medication states of PD patients.

Subjects will be recruited from the population of patients who are already implanted with DBS for treatment of PD. At the patient's follow up visit they will be asked to come to the clinic in the "off medication" state. Off medication is defined as at least 8 hours since the last medication dosing. Data will be collected during three phases: "OFF" state, transitioning state, and "ON" state. Subjects will be asked to assume different functional states (lying, sitting or walking) for 1 minute each. During these functional states, multiple measures of impedance will be collected. "OFF" state data collection: The subject will be examined to assess his motor examination score using the UPDRS-III. Measurements of impedance will be collected multiple times in the lying down and sitting up states. Transition state data collection: The subject will be asked to take their dopamine medication. The medication will take approximately 1 hour to take full effect. Measurements of impedance will be collected every 10 minutes during this transition from the "OFF" state to the "ON" state. Patients will be asked to report at what point they felt the "ON: state (they can report the state as "OFF", "unsure", "transition" or "ON"). "ON" state data collection: The "ON" state examination will start after 1 hour from medication administration. Subjects will be examined using the UPDRS-III. Measurements of impedance will be collected in the lying down, sitting and walking states. Summary of the study protocol: "OFF" state Transition state "ON' state UPDRS-III x x Impedance Lying down x x Sitting up x x x Walking x UPDRS I and II x Hoehn and Yahr x x

Dopaminergic medications are defined as either levodopa containing or dopamine agonist containing medications. The state is defined as the "OFF" state (medication effect is not present) and "ON" state (medication effect noted).

Inclusion Criteria: Idiopathic Parkinson's patients with DBS (unilateral or bilateral) Must be taking dopamine agonist or levodopa regimen Medtronic Neurostimulator Activa SC, PC or PC+S (IPG) Exclusion Criteria: Hoehn and Yahr (H&Y) 4 and above History of DBS revision or lead replacement surgery Current or prior non-Medtronic Activa SC, PC or PC+S IPG Historical information of more than 1 hour delay to "ON" state as average

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