CUSTOM-DBS: Current Steering to Optimize Deep Brain Stimulation

The therapeutic window refers to the range of stimulus amplitudes that provide a therapeutic effect without side effects. In other words, it is the amplitude difference between the first stimulation-induced side effect threshold (e.g., eye deviation, muscle contraction, and speech) and full rigidity control threshold at 60 µs and 30 µs pulse width DBS settings.

The Unified Parkinson's Disease Rating Scale (UPDRS) has four sections (I-IV) that ask patients to rate aspects of their mental state including mood (I), aspects of daily activities (II), aspects of motor function (III), and complications of treatment (IV). Here, we ask subjects to rate their motor function (UPDRS III) following interventions with 30 µs and 60 µs pulse width DBS settings.

The UPDRS III scale has 14 categories including speech, facial expression, tremor at rest, action tremor, rigidity, finger tapping ability, ability to open and close hands, ability to rapidly alternate hand movements, leg agility, ability to rise from a chair, posture, gait, response to postural displacement (e.g., push), and bradykinesia. Patients rate each of these categories from 0 to 4, with 0 being normal function and 4 being the worst. Categories assessing appendages are rated for both left and right sides, allowing a maximum score (worst outcome) of 108.

This endpoint determined how much current (mA) could be applied before side effects appeared when using 60 microsecond pulse widths. Values were obtained for when current was delivered through a single contact or divided between two contacts (steering).

Resting tremor was measured by a motion sensor system (Kinesia System) while either using a single contact or steering current between two contacts. Stimulation was at amplitudes defined as the therapeutic threshold for rigidity. The Kinesia System was worn by patients to measure motion parameters including linear acceleration and angular velocity during different tasks, then provided an output score on a scale of 0 (no symptoms) to 4 (severe symptoms).

Severity of finger-tapping bradykinesia was measured by a motion sensor system (Kinesia System) when either using a single contact or steering current between two contacts. Stimulation was at amplitudes defined as the therapeutic threshold for rigidity. The Kinesia System was worn by patients to measure motion parameters including linear acceleration and angular velocity during different tasks, then provided an output score on a scale of 0 (no symptoms) to 4 (severe symptoms).

The therapeutic window refers to the range of stimulus amplitudes that provide a therapeutic effect without side effects. In other words, this measure reports the stimulus amplitude difference between the full rigidity control threshold and the first stimulation induced side effect threshold at current steering settings (current divided 50% between adjacent electrodes).

Resting tremor was measured by a motion sensor system (Kinesia System) at 60 µs, 30 µs, and current steering settings, at amplitudes defined as the therapeutic threshold for rigidity. The Kinesia System was worn by patients to measure motion parameters including linear acceleration and angular velocity during different tasks, then provided an output score on a scale of 0 (no symptoms) to 4 (severe symptoms).

Severity of finger-tapping bradykinesia was measured by a motion sensor system (Kinesia System) at 60 µs, 30 µs, and dorsal and ventral current steering settings. Stimulation was at amplitudes defined as the therapeutic threshold for rigidity. The Kinesia System was worn by patients to measure motion parameters including linear acceleration and angular velocity during different tasks, then provided an output score on a scale of 0 (no symptoms) to 4 (severe symptoms).