- Movement and Neuroperformance Center of Colorado, 499 E Hampden Avenue, Suite 250, Englewood, Colorado, USA
Correspondence Address:
Sierra M. Farris
Movement and Neuroperformance Center of Colorado, 499 E Hampden Avenue, Suite 250, Englewood, Colorado, USA
DOI:10.4103/2152-7806.187532
Copyright: © 2016 Surgical Neurology International This is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.How to cite this article: Farris SM, Giroux ML. Rapid assessment of gait and speech after subthalamic deep brain stimulation. Surg Neurol Int 02-Aug-2016;7:
How to cite this URL: Farris SM, Giroux ML. Rapid assessment of gait and speech after subthalamic deep brain stimulation. Surg Neurol Int 02-Aug-2016;7:. Available from: http://surgicalneurologyint.com/surgicalint_articles/rapid-assessment-gait-speech-subthalamic-deep-brain-stimulation/
Abstract
Background:Describe a rapid assessment for patients with idiopathic Parkinson's disease (PD) and deep brain stimulation of the subthalamic nucleus reporting worsening speech and/or gait problems.
Methods:We retrospectively reviewed 29 patients that had improvement in gait and/or speech within 30 min after turning stimulation off. Clinical data analyzed include unified PD rating scale motor scores and stimulation parameters before and after adjusting stimulation. All patients received electrode efficacy and side effect threshold testing. Stimulation parameters were adjusted to maximize efficacy, avoid side effects, and maximize battery longevity.
Results:Turning stimulation off revealed reversible speech and/or gait stimulation side effects within 30 min. Focusing on six factors revealed stimulation modifications that improved motor symptoms, eliminated stimulation side effects, and reduced battery drain. Primary stimulation parameters modified were cathode selection and pulse width reduction.
Conclusions:Stimulation-induced side effects impacting gait and speech can be identified within 30 min. A systematic evaluation can distinguish disease progression from reversible stimulation side effects and improve motor outcomes over the long term.
Keywords: Deep brain stimulation, Parkinson's disease, side effects, subthalamic nucleus
INTRODUCTION
Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an effective treatment for idiopathic Parkinson's disease (IPD).[
METHODS
After retrospective review of 50 self-referred patients who underwent our DBS troubleshooting protocol in our movement disorders outpatient clinic, we identified 29 patients that had obvious speech and/or gait improvement on examination 30 min after turning off stimulation while in the medication off state. These patients are included in our analysis.
Unified PD rating scale motor (mUPDRS) examination off medicine/on stimulation (NOM/ONS). Medication off state was defined as at least 10 h since the last dose of dopaminergic medicine Stimulation is turned off for 30 min and the NOM/NOS mUPDRS is performed Impedance and battery analysis of the hardware system Our programing strategy mirrors recommendations provided by Krack et al.[ Stimulation parameters are further modified:
Electrode: The electrode providing the best motor response is selected Polarity: Monopolar[ Pulse width: 60 μs is the preferred pulse width (to maximize battery life and maximize the therapeutic window);[ Amplitude: The voltage associated with the onset of stimulation-induced side effect is noted, and the therapeutic voltage is calculated as 90% of the side effect threshold (i.e., side effects onset at 3.0 V therefore final voltage was 2.7)[ Frequency: Clinical efficacy is fine-tuned by testing a hertz range between 130 and 185 and selecting the lowest effective Hz[ Final stimulation settings are set, and an NOM/ONS mUPDRS is performed after 30 min Patients take their first-morning dose of PD medication A final ONM/ONS mUPDRS is completed, and voltage titrated down if dyskinesia is bothersome Patient home diaries are used to monitor dyskinesia, efficacy, and medication dosing between appointments. The rainbow passage,[ Medication is adjusted per change in off time or dyskinesia. Pre- and post-evaluation levodopa equivalent daily dose is calculated.[
RESULTS
Group characteristics are shown in
DISCUSSION
Our analysis finds gait and speech declines after STN DBS may be attributed to stimulation side effects and can be identified by clinical observation and examination within 30 min of turning off stimulation. Many of the referred patients reported a history of acute decline in gait and speech after a change in stimulation. Despite the history of an acute change, the patients’ dissatisfaction is what led to a second opinion. For each patient, we prioritized our time to investigate six factors that directly impact patient well-being with DBS.
First, we differentiated disease progression from stimulation-induced side effect by turning off stimulation. If gait, speech, or balance improves off stimulation, the time invested in adjusting stimulation can offer the patient a chance to be restored to their true disease stage. Even when disease progression is present, overstimulation can contribute to disease burden by worsening speech, swallowing, balance. and gait and is a modifiable factor impacting patient health and safety.
Second, each individual's levodopa response is their benchmark for optimal stimulation. Useful to set expectations before DBS surgery, levodopa-responsive symptoms remain responsive to stimulation and a reliable measure of DBS outcome. Motor examinations in the medication off and on state offer a greater understanding about speech and gait symptoms to establish clinical expectations for stimulation. This is illustrated in
Third, systematically mapping efficacy and side effects is a simple and proven method of testing stimulation parameters to find optimal therapy settings and essential to monitor for stimulation side effects at any time postsurgery.[
Fifth, stimulation outcome can be improved at any time postsurgery if the best stimulation settings have not been found. We chose the electrode that offered the most reduction in rigidity or bradykinesia and then adjusted the power using polarity, amplitude, and pulse width while being mindful of battery life. We used polarity and pulse width to make gross adjustments, whereas amplitude was used for fine adjustment. The amplitude that produced a very minor side effect was declared as the upper threshold of the therapeutic window (using 60 μs and 130 Hz) and provided guidance for polarity and pulse width. Our clinical protocol prioritizes amplitude to produce efficacy and pulse width, and polarity is minimized to avoid side effects. Our preference to conserve battery life is to increase pulse width >60 μs only if the maximal tolerated amplitude is >3.5 V. When pulse width is increased, less voltage is required to activate similar volumes of tissue but can coincide with an increase in stimulation side effects as described by Butson et al.[
The sixth factor we include is a focus on battery longevity to reduce the number of pulse generator replacements. Pulse generator longevity is influenced by power usage and programing attributes (interleaving can reduce longevity by 50%) and replacements carry a risk of morbidity.[
CONCLUSIONS
Our analysis focused on 29 patients with stimulation-induced gait and speech deficits that were rapidly detected and served to support the clinical time to conduct an in-depth review of factors that are known to directly impact clinical outcomes. Our findings suggest that disease progression may not be the only cause for a decline in speech and or gait after STN DBS and detection of stimulation side effects requires up to 30 min of time off stimulation. The minimal time to wash out gait and speech stimulation side effects remains unknown. Basic programing strategies continue to perform well in improving motor function and avoiding stimulation side effects. Although the electrode testing is easy to perform, the interpretation of efficacy and presence of stimulation side effects may pose a challenge as noted by the significant change in the stimulating electrode in our series. Our retrospective review is limited by an acute analysis of disease progression and change in stimulation parameters. Our assessment is further limited due to the absence of a formal gait or speech analysis which would enhance the mUPDRS and may offer additional clues to stimulation side effects.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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