Transient effects of 80 Hz stimulation on gait in STN DBS treated PD patients: A 15 months follow-up study

Correlation between deep brain stimulation effects on freezing of gait and audio-spinal reflex

OBJECTIVE

A network of cortical, subcortical and brainstem structures might be involved in freezing of gait (FOG). Subthalamic nucleus (STN) deep brain stimulation (DBS) could modulate this network. The audio-spinal reflex (ASR), reduced in PD, but increased by treatment, can be used to further investigate that locomotor network. The aim of this study is to find whether a correlation exists between ASR and FOG in PD patients under DBS.

METHODS

In 14 PD patients with STN DBS and previous FOG, ASR was recorded, with DBS switched on and off. We also assessed FOG Questionnaire (FOGQ) and Unified Parkinson's Disease Rating Scale (UPDRS) Part III.

RESULTS

Switching "on" DBS increased ASR amplitude (+ 33.2% with DBS ON, p = 0.048). We also found a significant inverse correlation between FOGQ and modulation of ASR by DBS (r = -0.59, r² = 0.35, p < 0.05).

CONCLUSIONS

This study shows that the incremental effect of DBS on ASR is greater in PD patients with less severe FOG.

SIGNIFICANCE

This study shows a link between electrophysiological and clinical data about gait control. It might contribute to better understand why some DBS patients report heavy FOG and others do not. ASR might be used to evaluate or maybe predict the effect of stimulation parameters changes on FOG.

Challenges in PD Patient Management After DBS: A Pragmatic Review

BACKGROUND

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) or internal globus pallidus (GPi) represents an effective and universally applied therapy for Parkinson's disease (PD) motor complications. However, certain procedure-related problems and unrealistic patient expectations may detract specialists from indicating DBS more widely despite significant clinical effects.

METHODS

This review provides a pragmatic educational summary of the most conflicting postoperative management issues in patients undergoing DBS for PD.

RESULTS

DBS in PD has been associated with certain complications and post-procedural management issues, which can complicate surgical outcome interpretation. Many PD patients consider DBS outcomes negative due to unfulfilled expectations, even when significant motor symptom improvement is achieved. Speech, gait, postural stability, and cognition may worsen after DBS and body weight may increase. Although DBS may induce impulse control disorders in some cases, in others, it may actually improve them when dopamine agonist dosage is reduced after surgery. However, apathy may also arise, especially when dopaminergic medication tapering is rapid. Gradual loss of response with time suggests disease progression, rather than the wearing off of DBS effects. Furthermore, implantable pulse generator expiration is considered a movement disorder emergency, as it may worsen parkinsonian symptoms or cause life-threatening akinetic crises due to malignant DBS withdrawal syndrome.

CONCLUSION

Major unsolved issues occurring after DBS therapy preclude complete patient satisfaction. Multidisciplinary management at experienced centers, as well as careful and comprehensive delivery of information to patients, should contribute to make DBS outcome expectations more realistic and allow post procedural complications to be better accepted.

Managing Gait, Balance, and Posture in Parkinson's Disease

PURPOSE OF REVIEW

Postural instability and gait difficulties inexorably worsen with Parkinson's disease (PD) progression and become treatment resistant, with a severe impact on autonomy and quality of life. We review the main characteristics of balance instability, gait disabilities, and static postural alterations in advanced PD, and the available treatment strategies.

RECENT FINDINGS

It remains very difficult to satisfactorily alleviate gait and postural disturbances in advanced PD. Medical and surgical interventions often fail to provide satisfactory or durable alleviation of these axial symptoms, that may actually call for differential treatments. Exercise and adapted physical activity programs can contribute to improving the patients' condition. Gait, balance, and postural disabilities are often lumped together under the Postural Instability and Gait Difficulties umbrella term. This may lead to sub-optimal patients' management as data suggest that postural, balance, and gait problems might depend on distinct underlying mechanisms. We advocate for a multidisciplinary approach from the day of diagnosis.

Deep Brain Stimulation of the Subthalamic Nucleus Parameter Optimization for Vowel Acoustics and Speech Intelligibility in Parkinson's Disease

PURPOSE

The settings of 3 electrical stimulation parameters were adjusted in 12 speakers with Parkinson's disease (PD) with deep brain stimulation of the subthalamic nucleus (STN-DBS) to examine their effects on vowel acoustics and speech intelligibility.

METHOD

Participants were tested under permutations of low, mid, and high STN-DBS frequency, voltage, and pulse width settings. At each session, participants recited a sentence. Acoustic characteristics of vowel production were extracted, and naive listeners provided estimates of speech intelligibility.

RESULTS

Overall, lower-frequency STN-DBS stimulation (60 Hz) was found to lead to improvements in intelligibility and acoustic vowel expansion. An interaction between speaker sex and STN-DBS stimulation was found for vowel measures. The combination of low frequency, mid to high voltage, and low to mid pulse width led to optimal speech outcomes; however, these settings did not demonstrate significant speech outcome differences compared with the standard clinical STN-DBS settings, likely due to substantial individual variability.

CONCLUSIONS

Although lower-frequency STN-DBS stimulation was found to yield consistent improvements in speech outcomes, it was not found to necessarily lead to the best speech outcomes for all participants. Nevertheless, frequency may serve as a starting point to explore settings that will optimize an individual's speech outcomes following STN-DBS surgery.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.5899228.

Neuromodulatory procedures for gait disorders in Parkinson's disease

The neurophysiology of gait is complex and involves numerous structures in the central nervous system. Gait disorders occur frequently in Parkinson's disease (PD), and their management may become cumbersome, especially in the more advanced stages. Neuromodulatory treatments, including deep brain stimulation, cortical stimulation and spinal cord stimulation, are reviewed with respect to their effectiveness to improve gait in PD patients. Although positive effects have been reported for all of these procedures, many issues remain in view of methodological heterogeneity, variability in outcome measures and sample size. Gait in PD remains a difficult issue with a tremendous impact on quality of life, for which future research is badly needed.

Subthalamic Nucleus Deep Brain Stimulation in Parkinson's Disease: The Effect of Varying Stimulation Parameters

Subthalamic Nucleus Deep Brain Stimulation (STN DBS) is a well-established and effective treatment modality for selected patients with Parkinson's disease (PD). Since its advent, systematic exploration of the effect of stimulation parameters including the stimulation intensity, frequency, and pulse width have been carried out to establish optimal therapeutic ranges. This review examines published data on these stimulation parameters in terms of efficacy of treatment and adverse effects. Altering stimulation intensity is the mainstay of titration in DBS programming via alterations in voltage or current settings, and is characterised by a lower efficacy threshold and a higher side effect threshold which define the therapeutic window. In addition, much work has been done in exploring the effects of frequency modulation, which may help patients with gait freezing and other axial symptoms. However, there is a paucity of data on the use of ultra-short pulse width settings which are now possible with technological advances. We also discuss current evidence for the use of novel programming techniques including directional and adaptive stimulation, and highlight areas for future research.

Advances in closed-loop deep brain stimulation devices

BACKGROUND

Millions of patients around the world are affected by neurological and psychiatric disorders. Deep brain stimulation (DBS) is a device-based therapy that could have fewer side-effects and higher efficiencies in drug-resistant patients compared to other therapeutic options such as pharmacological approaches. Thus far, several efforts have been made to incorporate a feedback loop into DBS devices to make them operate in a closed-loop manner.

METHODS

This paper presents a comprehensive investigation into the existing research-based and commercial closed-loop DBS devices. It describes a brief history of closed-loop DBS techniques, biomarkers and algorithms used for closing the feedback loop, components of the current research-based and commercial closed-loop DBS devices, and advancements and challenges in this field of research. This review also includes a comparison of the closed-loop DBS devices and provides the future directions of this area of research.

RESULTS

Although we are in the early stages of the closed-loop DBS approach, there have been fruitful efforts in design and development of closed-loop DBS devices. To date, only one commercial closed-loop DBS device has been manufactured. However, this system does not have an intelligent and patient dependent control algorithm. A closed-loop DBS device requires a control algorithm to learn and optimize the stimulation parameters according to the brain clinical state.

CONCLUSIONS

The promising clinical effects of open-loop DBS have been demonstrated, indicating DBS as a pioneer technology and treatment option to serve neurological patients. However, like other commercial devices, DBS needs to be automated and modernized.

Effect of low versus high frequency stimulation on freezing of gait and other axial symptoms in Parkinson patients with bilateral STN DBS: a mini-review

Some studies have shown that low frequency stimulation (LFS, most commonly 60 Hz), compared to high frequency stimulation (HFS, most commonly 130 Hz), has beneficial effects, short-term or even long-term, on improving freezing of gait (FOG) and other axial symptoms, including speech and swallowing function, in Parkinson disease (PD) patients with bilateral subthalamic nucleus deep brain stimulation (STN DBS). However, other studies failed to confirm this. It seems not clear what determines the difference in response to LFS. Differences in study design, such as presence or absence of FOG, exact LFS used (60 Hz versus 80 Hz), study size, open label versus randomized double blind assessment, retrospective versus prospective evaluation, medication On or Off state, total electric energy delivered maintained or not with the change in frequency, and the location of active contacts could all potentially affect the results. This mini-review goes over the literature with the aforementioned factors in mind, focusing on the effect of LFS versus HFS on FOG and other axial symptoms in PD with bilateral STN DBS, in an effort to extract the essential data to guide our clinical management of axial symptoms and explore the potential underlying mechanisms as well. Overall, LFS of 60 Hz seems to be consistently effective in patients with FOG at the usual HFS in regards to improving FOG, speech, swallowing function and other axial symptoms, though LFS could reduce tremor control in some patients. Whether LFS simply addresses the axial symptoms in the context of HFS or has other beneficial effects requires further studies, along with the mechanism.

Stratifying Parkinson's Patients With STN-DBS Into High-Frequency or 60 Hz-Frequency Modulation Using a Computational Model

OBJECTIVE

High frequency stimulation (HFS) of the subthalamic nucleus (STN) is a well-established therapy for Parkinson's disease (PD), particularly the cardinal motor symptoms and levodopa induced motor complications. Recent studies have suggested the possible role of 60 Hz stimulation in STN-deep brain stimulation (DBS) for patients with gait disorder. The objective of this study was to develop a computational model, which stratifies patients a priori based on symptomatology into different frequency settings (i.e., high frequency or 60 Hz).

METHODS

We retrospectively analyzed preoperative MDS-Unified Parkinson's Disease Rating Scale III scores (32 indicators) collected from 20 PD patients implanted with STN-DBS at Mount Sinai Medical Center on either 60 Hz stimulation (ten patients) or HFS (130-185 Hz) (ten patients) for an average of 12 months. Predictive models using the Random Forest classification algorithm were built to associate patient/disease characteristics at surgery to the stimulation frequency. These models were evaluated objectively using leave-one-out cross-validation approach.

RESULTS

The computational models produced, stratified patients into 60 Hz or HFS (130-185 Hz) with 95% accuracy. The best models relied on two or three predictors out of the 32 analyzed for classification. Across all predictors, gait and rest tremor of the right hand were consistently the most important.

CONCLUSIONS

Computational models were developed using preoperative clinical indicators in PD patients treated with STN-DBS. These models were able to accurately stratify PD patients into 60 Hz stimulation or HFS (130-185 Hz) groups a priori, offering a unique potential to enhance the utilization of this therapy based on clinical subtypes.

Subthalamic nucleus stimulation and gait in Parkinson's Disease: a not always fruitful relationship

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) provides efficient treatment for the alleviation of motor signs in patients with advanced Parkinson's disease (PD), but its specific effects on gait is sometimes less successful as it may even lead to an aggravation of freezing of gait. To better understand when axial symptoms can be expected to improve and when they may worsen or be resistant to STN-DBS, we propose here a narrative review that considers the recent literature evidences based on instrumental gait analysis data. Our aim is to report about the efficacy of STN-DBS on PD gait, analyzing the clinical and procedural factors involved, and discussing the strategies for optimizing such effectiveness in patients with advanced PD.

Freezing of Gait in Parkinsonism and its Potential Drug Treatment

Freezing of gait (FOG) is a heterogeneous symptom. Studies of treatment for FOG are scarce. Levodopa and monoamine oxidase inhibitors (rasagiline and selegiline) have shown effective improvement for FOG. Other drugs, such as L-threo-3, 4-dihydroxyphenylserine, amantadine, and botulinum toxin have exhibited some beneficial effects. The present review summarizes the potential drug treatment for FOG in Parkinsonism.

Sixty-hertz stimulation improves bradykinesia and amplifies subthalamic low-frequency oscillations

BACKGROUND

The objective of this study was to investigate the hypothesis that attenuation of subthalamic nucleus (STN) alpha-/beta-band oscillations is causal to improvement in bradykinesia.

METHODS

STN local field potentials from a sensing neurostimulator (Activa^® PC+S; Medtronic, Inc.) and kinematics from wearable sensors were recorded simultaneously during 60- and 140-Hz deep brain stimulation (DBS) in 9 freely moving PD subjects (15 STNs) performing repetitive wrist flexion-extension. Kinematics were recorded during 20-Hz DBS in a subgroup.

RESULTS

Both 60- and 140-Hz DBS improved the angular velocity and frequency of movement (P = 0.002 and P = 0.029, respectively, for 60 Hz; P < 0.001 and P < 0.001, respectively, for 140 Hz), but 60-Hz DBS did not attenuate beta-band power (13-30 Hz). In fact, 60-Hz DBS amplified alpha/low-beta (11-15 Hz, P = 0.007) and attenuated high-beta power (19-27 Hz, P < 0.001), whereas 140-Hz DBS broadly attenuated beta power (15-30 Hz, P < 0.001). Only 60-Hz DBS improved the regularity of angular range (P = 0.046) and 20-Hz DBS did not worsen bradykinesia. There was no correlation between beta-power modulation and bradykinesia.

CONCLUSIONS

These novel results obtained from freely moving PD subjects demonstrated that both 140- and 60-Hz DBS improved bradykinesia and attenuated high beta oscillations; however, 60-Hz DBS amplified a subband of alpha/low-beta oscillations, and DBS at a beta-band frequency did not worsen bradykinesia. Based on recent literature, we suggest that both 140- and 60-Hz DBS decouple the cortico-STN hyperdirect pathway, whereas 60-Hz DBS increases coupling within striato-STN circuitry. These results inform future algorithms for closed-loop DBS in PD. © 2016 International Parkinson and Movement Disorder Society.

Current Topics in Deep Brain Stimulation for Parkinson Disease

There is a long history of surgical treatment for Parkinson disease (PD). After pioneering trials and errors, the current primary surgical treatment for PD is deep brain stimulation (DBS). DBS is a promising treatment option for patients with medically refractory PD. However, there are still many problems and controversies associated with DBS. In this review, we discuss current issues in DBS for PD, including patient selection, clinical outcomes, complications, target selection, long-term outcomes, management of axial symptoms, timing of surgery, surgical procedures, cost-effectiveness, and new technology.

Deep brain stimulation for Parkinson's disease: current status and future outlook

Parkinson's disease is a neurodegenerative condition secondary to loss of dopaminergic neurons in the substantia nigra pars compacta. Surgical therapy serves as an adjunct when unwanted medication side effects become apparent or additional therapy is needed. Deep brain stimulation emerged into the forefront in the 1990s. Studies have demonstrated improvement in all of the cardinal parkinsonian signs with stimulation. Frameless and ‘mini-frame’ stereotactic systems, improved MRI for anatomic visualization, and intraoperative MRI-guided placement are a few of the surgical advances in deep brain stimulation. Other advances include rechargeable pulse generators, voltage- or current-based stimulation, and enhanced abilities to ‘steer’ stimulation. Work is ongoing investigating closed-loop ‘smart’ stimulation in which stimulation is predicated on neuronal feedback.

Low-frequency deep brain stimulation for Parkinson's disease: Great expectation or false hope?

The long-term efficacy of subthalamic deep brain stimulation for Parkinson's disease is not always retained, and many patients lose the improvement achieved during the "second honeymoon" following surgery. Deep brain stimulation is a versatile tool, as stimulation parameters may undergo a fine-tuning depending on clinical needs. Among them, frequency is the parameter that leads to more complex scenarios because there is no generalizable relationship between its modulation and the overall clinical response, which also depends on the specific considered sign. High-frequency stimulation (>100 Hz) has shown to be effective in improving most parkinsonian signs, particularly the levodopa-responsive ones. However, its effect on axial signs (such as balance, gait, speech, or swallowing) may not be sustained, minimal, or even detrimental. For these reasons, several studies have explored the effectiveness of low-frequency stimulation (generally 60 or 80 Hz). Methods, results, and especially interpretations of these studies are quite variable. Although the use of low-frequency stimulation certainly opens new avenues in the field of deep brain stimulation, after having gathered all the available evidence in patients with subthalamic implants, our conclusion is that it might be clinically useful mainly when it lessens the detrimental effects of high-frequency stimulation. © 2016 International Parkinson and Movement Disorder Society.

Low-frequency Subthalamic Stimulation in Parkinson's Disease: Long-term Outcome and Predictors

BACKGROUND

Parkinson's disease patients undergoing subthalamic nucleus deep brain stimulation (STN DBS) at standard frequency (>100 Hz) often develop gait impairment, postural instability and speech difficulties. Low frequency stimulation (<100 Hz, LFS) can improve such axial symptoms, but there are concerns that improvement may be transient.

OBJECTIVE

To identify long-term outcome and predictors of low-frequency subthalamic stimulation in Parkinson's disease.

METHODS

Through a chart review we identified 85 out of 324 STN DBS patients who received a trial of LFS and describe their characteristics and outcome predictors.

RESULTS

Patients were switched to LFS (<100 Hz) 3.8 ± 3.3 years after surgery. Most patients (64%) attained a subjective improvement of gait, speech or balance for 2.0 ± 1.9 years. Motor scores improved within the first year after the stimulation change and showed a slower progression over time when compared to patients switched back to high frequency stimulation. UPDRS III axial score on medication before surgery and the y-axis coordinate of the active contact were independent predictors of LFS retention.

CONCLUSIONS

This report provides evidence that the use of LFS yields an enduring benefit in a considerable percentage of patients who develop axial motor symptoms during conventional stimulation.

Effect of low-frequency deep brain stimulation on sensory thresholds in Parkinson's disease

OBJECTIVE Chronic pain is a major distressing symptom of Parkinson's disease (PD) that is often undertreated. Subthalamic nucleus (STN) deep brain stimulation (DBS) delivers high-frequency stimulation (HFS) to patients with PD and has been effective in pain relief in a subset of these patients. However, up to 74% of patients develop new pain concerns while receiving STN DBS. Here the authors explore whether altering the frequency of STN DBS changes pain perception as measured through quantitative sensory testing (QST). METHODS Using QST, the authors measured thermal and mechanical detection and pain thresholds in 19 patients undergoing DBS via HFS, low-frequency stimulation (LFS), and off conditions in a randomized order. Testing was performed in the region of the body with the most pain and in the lower back in patients without chronic pain. RESULTS In the patients with chronic pain, LFS significantly reduced heat detection thresholds as compared with thresholds following HFS (p = 0.029) and in the off state (p = 0.010). Moreover, LFS resulted in increased detection thresholds for mechanical pressure (p = 0.020) and vibration (p = 0.040) compared with these thresholds following HFS. Neither LFS nor HFS led to changes in other mechanical thresholds. In patients without chronic pain, LFS significantly increased mechanical pain thresholds in response to the 40-g pinprick compared with thresholds following HFS (p = 0.032). CONCLUSIONS Recent literature has suggested that STN LFS can be useful in treating nonmotor symptoms of PD. Here the authors demonstrated that LFS modulates thermal and mechanical detection to a greater extent than HFS. Low-frequency stimulation is an innovative means of modulating chronic pain in PD patients receiving STN DBS. The authors suggest that STN LFS may be a future option to consider when treating Parkinson's patients in whom pain remains the predominant complaint.

High Frequency Deep Brain Stimulation and Neural Rhythms in Parkinson's Disease

High frequency (HF) deep brain stimulation (DBS) is an established therapy for the treatment of Parkinson's disease (PD). It effectively treats the cardinal motor signs of PD, including tremor, bradykinesia, and rigidity. The most common neural target is the subthalamic nucleus, located within the basal ganglia, the region most acutely affected by PD pathology. Using chronically-implanted DBS electrodes, researchers have been able to record underlying neural rhythms from several nodes in the PD network as well as perturb it using DBS to measure the ensuing neural and behavioral effects, both acutely and over time. In this review, we provide an overview of the PD neural network, focusing on the pathophysiological signals that have been recorded from PD patients as well as the mechanisms underlying the therapeutic benefits of HF DBS. We then discuss evidence for the relationship between specific neural oscillations and symptoms of PD, including the aberrant relationships potentially underlying functional connectivity in PD as well as the use of different frequencies of stimulation to more specifically target certain symptoms. Finally, we briefly describe several current areas of investigation and how the ability to record neural data in ecologically-valid settings may allow researchers to explore the relationship between brain and behavior in an unprecedented manner, culminating in the future automation of neurostimulation therapy for the treatment of a variety of neuropsychiatric diseases.

When battery exhaustion lets the lame walk: a case report on the importance of long-term stimulator monitoring in deep brain stimulation

Background

Deep brain stimulation is increasingly used in the treatment of advanced Parkinson’s disease. While its short-term effectiveness is well documented, there are only few reports on long-term outcomes, and the need to repeatedly reprogram the stimulator is seldom reported.

Case presentation

We present a 74-year-old man with gait impairment, which had been mistaken for worsening of the disease and only remitted when the stimulator battery was exhausted indicating that the stimulator itself had been the cause.

Conclusion

This case highlights the need to repeatedly monitor not only battery capacity, but also stimulator-related side-effects for an extended period after implantation and, if necessary, to refer to centres capable of systematically reprogramming the device.

Freezing of gait: a practical approach to management

Freezing of gait is a common and disabling symptom in patients with parkinsonism, characterised by sudden and brief episodes of inability to produce effective forward stepping. These episodes typically occur during gait initiation or turning. Treatment is important because freezing of gait is a major risk factor for falls in parkinsonism, and a source of disability to patients. Various treatment approaches exist, including pharmacological and surgical options, as well as physiotherapy and occupational therapy, but evidence is inconclusive for many approaches, and clear treatment protocols are not available. To address this gap, we review medical and non-medical treatment strategies for freezing of gait and present a practical algorithm for the management of this disorder, based on a combination of evidence, when available, and clinical experience of the authors. Further research is needed to formally establish the merits of our proposed treatment protocol.

Early Use of 60 Hz Frequency Subthalamic Stimulation in Parkinson's Disease: A Case Series and Review

BACKGROUND

Deep brain stimulation (DBS) is effective in treating the segmental symptoms of Parkinson's disease (PD) as well as axial symptoms that are levodopa responsive. PD patients on chronic DBS who develop axial symptoms and gait disturbances several years later oftentimes are refractory to high frequency stimulation (HFS). Several studies report benefit produced by low frequency subthalamic nucleus (STN) stimulation in such patients, though the sustainability of the effects has been mixed.

OBJECTIVE

To report the clinical outcomes of a series of patients with Parkinson's disease and levodopa responsive axial and gait disturbances who were switched to 60 Hz stimulation within one year of their DBS surgery.

METHODS

A retrospective review of 5 patients, whose severe pre-DBS, levodopa responsive gait disorders worsened on HFS STN-DBS and were subsequently switched to 60 Hz stimulation within 1 year of their surgery.

RESULTS

The median age of this cohort was 66 years with median disease duration of 14 years. Four of 5 patients' experienced acute worsening of their axial and gait UPDRS III scores on HFS. All patients' gait disorder improved with 60 Hz along with amelioration of their segmental symptoms and reduction of their levodopa induced dyskinesia. The median time on HFS prior to switching to 60 Hz was two months. Stimulation through the ventral contacts was utilized in all patients with relatively modest changes achieved in levodopa equivalent daily dose.

CONCLUSION

This case series demonstrates the clinical efficacy of utilizing low frequency (60 Hz) STN stimulation early in the DBS programming course in more advanced PD patients with levodopa responsive gait disturbance and freezing of gait. Activation of a broader stimulation field likely contributed to both axial and segmental symptom improvement while possibly aiding in the reduction of dyskinesia.

Axial disability and deep brain stimulation in patients with Parkinson disease

Axial motor signs-including gait impairment, postural instability and postural abnormalities-are common and debilitating symptoms in patients with advanced Parkinson disease. Dopamine replacement therapy and physiotherapy provide, at best, partial relief from axial motor symptoms. In carefully selected candidates, deep brain stimulation (DBS) of the subthalamic nucleus or globus pallidus internus is an established treatment for 'appendicular' motor signs (limb tremor, bradykinesia and rigidity). However, the effects of DBS on axial signs are much less clear, presumably because motor control of axial and appendicular functions is mediated by different anatomical-functional pathways. Here, we discuss the successes and failures of DBS in managing axial motor signs. We systematically address a series of common clinical questions associated with the preoperative phase, during which patients presenting with prominent axial signs are considered for DBS implantation surgery, and the postoperative phase, in particular, the management of axial motor signs that newly develop as postoperative complications, either acutely or with a delay. We also address the possible merits of new targets-including the pedunculopontine nucleus area, zona incerta and substantia nigra pars reticulata-to specifically alleviate axial symptoms. Supported by a rapidly growing body of evidence, this practically oriented Review aims to support decision-making in the management of axial symptoms.

Axial disability and deep brain stimulation in patients with Parkinson disease

Axial motor signs-including gait impairment, postural instability and postural abnormalities-are common and debilitating symptoms in patients with advanced Parkinson disease. Dopamine replacement therapy and physiotherapy provide, at best, partial relief from axial motor symptoms. In carefully selected candidates, deep brain stimulation (DBS) of the subthalamic nucleus or globus pallidus internus is an established treatment for 'appendicular' motor signs (limb tremor, bradykinesia and rigidity). However, the effects of DBS on axial signs are much less clear, presumably because motor control of axial and appendicular functions is mediated by different anatomical-functional pathways. Here, we discuss the successes and failures of DBS in managing axial motor signs. We systematically address a series of common clinical questions associated with the preoperative phase, during which patients presenting with prominent axial signs are considered for DBS implantation surgery, and the postoperative phase, in particular, the management of axial motor signs that newly develop as postoperative complications, either acutely or with a delay. We also address the possible merits of new targets-including the pedunculopontine nucleus area, zona incerta and substantia nigra pars reticulata-to specifically alleviate axial symptoms. Supported by a rapidly growing body of evidence, this practically oriented Review aims to support decision-making in the management of axial symptoms.

A critical reflection on the technological development of deep brain stimulation (DBS)

Since the translational research findings of Benabid and colleagues which partly led to their seminal paper regarding the treatment of mainly tremor-dominant Parkinson patients through thalamic high-frequency-stimulation (HFS) in 1987, we still struggle with identifying a satisfactory mechanistic explanation of the underlying principles of deep brain stimulation (DBS). Furthermore, the technological advance of DBS devices (electrodes and implantable pulse generators, IPG’s) has shown a distinct lack of dynamic progression. In light of this we argue that it is time to leave the paleolithic age and enter hellenistic times: the device-manufacturing industry and the medical community together should put more emphasis on advancing the technology rather than resting on their laurels.

Effects of deep brain stimulation of the subthalamic nucleus on freezing of gait in Parkinson's disease: a prospective controlled study

BACKGROUND

Freezing of gait (FOG) is a debilitating gait disorder in Parkinson's disease (PD) with partial responsiveness to dopaminergic medication. To date, notions about the effects of subthalamic deep brain stimulation (STN-DBS) on FOG remain controversial.

OBJECTIVES

To compare the effects of bilateral STN-DBS and continued best medical treatment (BMT) on FOG occurrence, FOG severity and clinical outcomes in PD patients at 6 and 12 months follow-up.

METHODS

In this prospective, controlled study, 41 PD patients with at least 5 years disease duration participated. Twenty-four subjects (20 with FOG) were treated with STN-DBS and seventeen (15 with FOG) continued BMT. The primary outcome was the New Freezing of Gait Questionnaire (NFOGQ) at 6 months postsurgery. Other outcomes were the NFOGQ at 12 months and clinical outcomes (Unified Parkinson's Disease Rating Scale III (UPDRS III), timed gait, falls and quality of life) at both time points.

RESULTS

STN-DBS increased the likelihood to convert from being a freezer to a non-freezer at 6 and 12 months follow-up (relative risk reduction=0.4). However, 45% of baseline freezers still experienced FOG 6 and 12 months postsurgery although with reduced severity. Three baseline non-freezers (1/2 BMT-treated, 2/4 STN-DBS-treated) developed FOG during follow-up. STN-DBS-induced benefits on FOG were mostly mediated by baseline levodopa equivalent dose, altered medication-intake and reduced motor fluctuations.

CONCLUSIONS

In contrast to continued BMT, STN-DBS reduced FOG occurrence and severity at 6 months postsurgery with largely sustained effects at 12 months follow-up. Longer follow-up periods are needed to test whether FOG improvements after STN-DBS persist with disease progression.

A neurochemical closed-loop controller for deep brain stimulation: toward individualized smart neuromodulation therapies

Current strategies for optimizing deep brain stimulation (DBS) therapy involve multiple postoperative visits. During each visit, stimulation parameters are adjusted until desired therapeutic effects are achieved and adverse effects are minimized. However, the efficacy of these therapeutic parameters may decline with time due at least in part to disease progression, interactions between the host environment and the electrode, and lead migration. As such, development of closed-loop control systems that can respond to changing neurochemical environments, tailoring DBS therapy to individual patients, is paramount for improving the therapeutic efficacy of DBS. Evidence obtained using electrophysiology and imaging techniques in both animals and humans suggests that DBS works by modulating neural network activity. Recently, animal studies have shown that stimulation-evoked changes in neurotransmitter release that mirror normal physiology are associated with the therapeutic benefits of DBS. Therefore, to fully understand the neurophysiology of DBS and optimize its efficacy, it may be necessary to look beyond conventional electrophysiological analyses and characterize the neurochemical effects of therapeutic and non-therapeutic stimulation. By combining electrochemical monitoring and mathematical modeling techniques, we can potentially replace the trial-and-error process used in clinical programming with deterministic approaches that help attain optimal and stable neurochemical profiles. In this manuscript, we summarize the current understanding of electrophysiological and electrochemical processing for control of neuromodulation therapies. Additionally, we describe a proof-of-principle closed-loop controller that characterizes DBS-evoked dopamine changes to adjust stimulation parameters in a rodent model of DBS. The work described herein represents the initial steps toward achieving a “smart” neuroprosthetic system for treatment of neurologic and psychiatric disorders.

Low-frequency subthalamic nucleus stimulation in Parkinson's disease: a randomized clinical trial

BACKGROUND

Low-frequency, bilateral stimulation of the subthalamic nucleus can improve axial symptoms of advanced Parkinson's disease (PD), but it is not particularly effective for segmental symptoms.

METHODS

The optimal contacts for low-frequency (60 Hz) and high-frequency (130 Hz) single monopolar stimulation were determined. Then, in a randomized, double-blind, prospective crossover manner, 60-Hz and 130-Hz stimulations via the respective optimal contacts were compared for immediate efficacy in improving the motor function of patients with PD.

RESULTS

The optimal contacts for 60-Hz stimulation were situated more ventrally than those for 130-Hz stimulation (P = 0.038). Under the respective optimal, single monopolar stimulation, 60 Hz provided superior efficacy over 130 Hz in improving the total Unified Parkinson's Disease Rating Scale motor score (P < 0.001) and the akinesia (P = 0.011) and axial motor signs (P = 0.012) subscores without compromising the therapeutic effect on tremor and rigidity.

CONCLUSIONS

Low-frequency stimulation via the optimal contacts is effective in improving overall motor function of patients with PD.

60-Hz frequency effect on gait in Parkinson's disease with subthalamic nucleus deep brain stimulation

OBJECTIVE

Gait dysfunction is common in advancing Parkinson's disease and has a disappointing response to dopamine replacement and subthalamic nucleus deep brain stimulation programming parameters. Low-frequency stimulation, less than 130 Hz in combination with increased voltage, has been shown to decrease freezing episodes and number of steps with little impact on overall performance measured by the Unified Parkinson's Disease Rating Scale. This was in the setting of delivering the same total energy, which required both a change in voltage and frequency. We wanted to determine if the benefit came from low frequency alone.

MATERIALS AND METHODS

We enrolled 20 Parkinson's patients who were at least three months in postbilateral subthalamic deep brain stimulation and reported gait changes. Subjects held their Parkinson's medications overnight, and following a baseline evaluation, they were randomly assigned to both 60 and 130 Hz stimulation in a blinded fashion with all other parameters held constant. Each subject was set at each frequency twice during the study, with a 60-min stimulation interval prior to each gait evaluation.

RESULTS

There was no significant difference between the two frequencies, with the primary outcome measure of stride length. Two of the 20 patients reported a significant subjective improvement in their gait with no statistical difference in their outcomes. There also was less tremor control at 60 Hz.

CONCLUSION

We were unable to demonstrate improved gait with lower frequency stimulation as suggested by prior studies. This may have been because of the decreased energy delivered from the lower frequency and unchanged voltage.

Nigral stimulation for resistant axial motor impairment in Parkinson's disease? A randomized controlled trial

Gait and balance disturbances typically emerge in advanced Parkinson’s disease with generally limited response to dopaminergic medication and subthalamic nucleus deep brain stimulation. Therefore, advanced programming with interleaved pulses was put forward to introduce concomittant nigral stimulation on caudal contacts of a subthalamic lead. Here, we hypothesized that the combined stimulation of subthalamic nucleus and substantia nigra pars reticulata improves axial symptoms compared with standard subthalamic nucleus stimulation. Twelve patients were enrolled in this 2 × 2 cross-over double-blind randomized controlled clinical trial and both the safety and efficacy of combined subthalamic nucleus and substantia nigra pars reticulata stimulation were evaluated compared with standard subthalamic nucleus stimulation. The primary outcome measure was the change of a broad-scaled cumulative axial Unified Parkinson’s Disease Rating Scale score (Scale II items 13–15, Scale III items 27–31) at ‘3-week follow-up’. Secondary outcome measures specifically addressed freezing of gait, balance, quality of life, non-motor symptoms and neuropsychiatric symptoms. For the primary outcome measure no statistically significant improvement was observed for combined subthalamic nucleus and substantia nigra pars reticulata stimulation at the ‘3-week follow-up’. The secondary endpoints, however, revealed that the combined stimulation of subthalamic nucleus and substantia nigra pars reticulata might specifically improve freezing of gait, whereas balance impairment remained unchanged. The combined stimulation of subthalamic nucleus and substantia nigra pars reticulata was safe, and of note, no clinically relevant neuropsychiatric adverse effect was observed. Patients treated with subthalamic nucleus and substantia nigra pars reticulata stimulation revealed no ‘global’ effect on axial motor domains. However, this study opens the perspective that concomittant stimulation of the substantia nigra pars reticulata possibly improves otherwise resistant freezing of gait and, therefore, highly warrants a subsequent phase III randomized controlled trial.

Surgical treatment of Parkinson disease: past, present, and future

Advances in functional neurosurgery have expanded the treatment of Parkinson disease (PD) to targeted electrical stimulation of specific nodes in the basal ganglia circuitry. Deep brain stimulation (DBS), applied to selected patients and difficult-to-manage motor fluctuations, yields substantial reductions in off time and dyskinesia. Emerging concepts in DBS include examination of new targets, such as the potential efficacy of pedunculopontine nucleus stimulation for treatment of freezing and falls, the use of pathologic oscillations in the beta band to construct an adaptive "closed-loop" DBS, and new technologies, including segmented electrodes to steer current toward specific neural populations.

80 Hz versus 130 Hz subthalamic nucleus deep brain stimulation: effects on involuntary movements

BACKGROUND

Subthalamic Nucleus Deep Brain Stimulation (STN-DBS) represents a valid therapeutic option for advanced Parkinson's disease (PD), leading to a significant amelioration of motor fluctuations and levodopa-induced involuntary movements (IM). This study address the issue of whether stimulation frequency may influence the control of IM in STN-DBS treated patients, comparing the effects of 80 Hz and 130 Hz STN-DBS frequencies in 10 parkinsonian patients with residual IM (dyskinesia in 6 cases and dystonia in 4 cases).

METHODS

Patients were evaluated by means of the Rush Dyskinesias Rating Scale (blinded-video analysis) and Unified Parkinson's Disease Rating Scale at 4 different time-points: baseline, shortly after the switch of stimulation frequency from 130 Hz to 80 Hz, after 1 month and 12 months of chronic 80 Hz stimulation.

RESULTS

IM improved in most subjects after the switch of stimulation frequency: dyskinesias improved in 6/6 subjects and dystonic features in 3/4 subjects after one month of 80 Hz stimulation. However, the 130 Hz STN stimulation was restored in 4 subjects during the following months, because of a gradual worsening of parkinsonian symptoms. A sustained efficacy on motor features and IM was observed with 80 Hz stimulation frequency in the remaining patients.

CONCLUSIONS

In this limited cohort of STN-DBS patients, we observed an improvement of residual IM after the switch of stimulation frequency from 130 Hz to 80 Hz. However, a moderate worsening of parkinsonian symptoms was observed in a portion of patients, requiring to return at 130 Hz STN-DBS.

Postoperative management of deep brain stimulation in Parkinson's disease

Deep brain stimulation has become an established treatment for advanced Parkinson's disease. Its postoperative management is a delicate phase, dedicated to finding the optimal balance between stimulation and dopaminergic treatment. Postoperative management can be divided into an acute phase, aimed at the selection of the best stimulation contact, and a stabilization phase, aimed at the progressive adjustment of stimulation parameters and medications. A good knowledge of the electrophysiological anatomy of the target and surrounding structures, of the potential consequences of dopaminergic treatment modifications, and of the time course and interactions between stimulation and medication effects is mandatory for optimal outcome. This chapter focuses on the main strategies for the acute and chronic management of stimulation parameters and medication in the three main nuclei targeted in Parkinson's disease, namely the subthalamic nucleus, the ventral intermediate thalamic nucleus, and the internal part of the globus pallidus.