Abstract

BackgroundThis study evaluated the impact of sociodemographic factors, surgical modalities, and commercially available options of electrodes on deep brain stimulation (DBS) outcomes in Parkinson’s disease.

MethodsWe retrospectively analyzed 59 elective DBS surgeries performed at a single institution from 2016 to 2023. Hoehn and Yahr (HY) scale scores and levodopa equivalent daily dosages (LEDD) were assessed at baseline, 3 months, and 6 months postoperatively. Collected variables included length of stay (LOS), age, sex, race/ethnicity, language, body mass index, insurance status, marital status, religion, type of anesthesia, concurrent pulse generator implantation, location of the implant, and conventional or directional lead. DBS systems included Medtronic, Boston Scientific, and Abbott (also known as St. Jude Medical).

ResultsThe mean LOS was 2.36 days. Mean HY scores improved from baseline (3.17) to 3 months (2.83) and 6 months (2.85), and LEDD significantly decreased at both 3 and 6 months postoperatively. Divorced patients showcased a significantly larger improvement in HY scores at 3 months compared to other marital groups. Abbott leads were associated with a significantly longer LOS compared to Boston Scientific (+1.85 days) and Medtronic (+2 days). No other variables significantly affected DBS outcomes.

ConclusionThis study investigated the impact of sociodemographic factors and surgical modalities of DBS in PD patients, showcasing how DBS improved motor function and reduced medication usage at 3 and 6 months postoperative. Marital status and lead manufacturer significantly influenced DBS outcomes, highlighting the importance of personalized considerations in DBS management.

Keywords: Deep brain stimulation, Functional neurosurgery, Neuromodulation, Parkinson’s disease, Sociodemographics

INTRODUCTION

Parkinson’s disease (PD) is a neurodegenerative disorder resulting from the loss of dopaminergic neurons in the substantia nigra of the midbrain.[ 1 ] Lewy bodies are key sightings of patients with PD, with tremors, rigidity, and bradykinesia being the main triad of symptoms.[ 23 ] Despite there being over 6 million cases reported globally and the prevalence expected to double by 2040,[ 7 , 36 ] there are currently no known cures for PD, highlighting the importance of methods of treatment to relieve symptoms. While many treatment options are available for PD, deep brain stimulation (DBS) has been utilized in increasing frequency due to its advantages compared to medication-based treatments as well as past surgical treatments that often involved irreversibly lesioning parts of the brain.[ 2 ] DBS involves implanting electrodes on parts of the brain involved with Parkinson’s, most commonly the subthalamic nucleus (STN) and globus pallidus interna (GPi), and providing electrical stimulation to improve symptoms.[ 8 , 41 ] In more recent years, interest has grown around enhancing efficacy and technology, improving outcomes, and reducing adverse effects of DBS.[ 37 ] Investigation into different modalities of DBS has included variables such as implantation location, type of anesthesia,[ 14 ] and conventional or directional leads.[ 26 , 43 ] Conventional leads use ring-shaped electrodes that generate an approximately spherical electrical field, while directional electrodes are radially segmented and allow the stimulation field to be moved in the horizontal plane or for the current to be steered in a particular direction.[ 40 ] While the literature has shown that there seems to be no difference in primary outcomes between general anesthesia (GA) and local anesthesia (LA),[ 19 ] implantation of directional leads has showcased both advantages and challenges compared to conventional leads.[ 24 , 25 , 27 ] A better understanding is needed of the benefits of different modalities of DBS. In addition, no study has investigated differences between current commercially available directional leads and the effects of social determinants of health on DBS outcomes have yet to be established.[ 37 ] To address these needs, this study aimed to evaluate different modalities of DBS in Parkinson’s patients as well as to investigate the differences between commercially available options for electrodes. Another goal of this study was to evaluate for differences in DBS outcomes based on patient demographics and anthropometrics.

MATERIALS AND METHODS

Following Institutional Review Board (IRB) approval (#5230488), we analyzed 59 elective DBS surgeries performed from 2016 to 2023 using our institution’s database of longitudinally collected electronic medical information. Patient consent was not required due to the nature of this retrospective chart review study. All patients included in the study were considered based on a diagnosis of PD, current indications and selection criteria for DBS, subsequent DBS surgery, and successful 3 and 6-month postoperative follow-up.[ 32 , 33 ] Exclusion criteria consisted of patients with existing neurological hardware, previous neurological surgery, traumatic brain injury, infection, malignancy, and patients who were lost to follow-up. Patient demographic data collected consisted of age, sex, race, ethnicity, language, body mass index (BMI), insurance status, marital status, and religion and were obtained through the patient’s self-reported answers in the electronic medical record.

Hoehn and Yahr (HY) scale scores were collected from the patient’s preoperative visit, 3-month postoperative visit, and 6-month postoperative visit, which evaluated the severity of functional disability associated with PD.[ 18 ] While a modified HY scale with 0.5 increments exists, the original five-point scale was maintained due to recommendations from the Movement Disorder Society (MDS) task force for rating scales for PD.[ 13 ] Additional variables collected consisted of the type of anesthesia utilized for the DBS procedure (LA or GA) if the operation concurrently included pulse generator implantation (yes or no), location of the implant (STN or GPi), hospital length of stay (LOS) after the DBS procedure, type of lead (conventional or directional), and levodopa equivalent daily dosage (LEDD). LEDD was calculated based on patient medication lists utilizing the conversion formulas provided by Tomlinson et al.[ 46 ] Categories of different commercially available options for DBS leads were determined to be Medtronic, Boston Scientific, and Abbott (also known as St. Jude Medical).[ 26 ] Table 1 showcases a list of collected variables.

Table 1:

Collected variables and number of patients.

Statistical analyses

Data collection and visualization were performed using Microsoft Excel version 16.58 (Microsoft Corporation, 2022, Redmond, WA, USA). The Statistical Package for the Social Sciences version 28 (IBM Corporation, 2021, Armonk, NY, USA) was utilized for all subsequent statistical analyses with alpha defined as P < 0.05. Associations were assessed among patient demographic and anthropometric variables, DBS procedure-specific variables, and DBS outcomes. DBS outcomes were measured through hospital LOS after DBS implantation, the difference between preoperative and 3-month postoperative HY scores, and the difference between preoperative and 6-month postoperative HY scores.

Age, BMI, and LOS were categorized as continuous variables and were analyzed utilizing a linear regression analysis, with Pearson correlation tests performed to assess associations. Sex, insurance, language, type of anesthesia, concurrent pulse generator implantation, implantation location, and type of lead were considered categorical variables and were analyzed through an independent sample t-test with equal variances not assumed/assumed, based on Levene’s test of variance. Regarding race, religion, and marital status, a one-way analysis of variance (ANOVA) with Bonferroni and Tukey post hoc analysis was utilized for the analysis of significance between groups. Differences in DBS outcomes modality based on the manufacturer of lead were assessed using a multiple variable ANOVA with post hoc Bonferroni and Tukey corrections.

RESULTS

Cohort description

Of the 59 patients included in this study, 41 were male, and 18 were female. With respect to race and ethnicity, 41 were White, 16 were Hispanic, and 2 were Asian. The mean patient age was 67.15 years, and the mean BMI was 27.29 kg/m². Regarding language, 52 preferred English, 6 preferred Spanish, and one patient’s preferred language was unavailable and was subsequently withheld from analysis. Fifty-four operations were bilateral implantations. Twenty-two patients utilized conventional leads, and 37 utilized directional leads. Regarding DBS lead manufacturers, the leads utilized were from Medtronic, Boston Scientific, and Abbott. Thirty-three patients utilized Medtronic, 18 utilized Boston Scientific, and 8 utilized Abbott. The mean LOS was 2.36 days. The mean HY preoperative score was 3.17; the mean HY 3-month postoperative score was 2.83; the mean HY 6-month postoperative score was 2.85; the mean preoperative LEDD was 1098 mg; mean 3-month postoperative LEDD was 916 mg, and mean 6-month postoperative LEDD was 773 mg. Table 1 showcases a description of our cohort along with collected variables.

Patient demographics and anthropometrics

Tables 2 and 3 showcase differences in DBS outcomes based on patient demographic and anthropometric variables for 3-month and 6-month postoperative HY scores, respectively. Regarding marital status, divorced patients showcased significantly larger mean differences (MDs) between preoperative and 3-month postoperative HY scores compared to all other relationship groups. No other statistically significant associations were found between DBS outcomes and patient demographic and anthropometric variables.

Table 2:

Differences in deep brain stimulation outcomes based on patient demographics and anthropometrics.

Table 3:

Differences in deep brain stimulation outcomes based on patient demographics and anthropometrics.

Modalities of DBS

Table 4 showcases differences in outcomes based on the modality of DBS. Table 5 showcases differences in DBS outcomes based on manufacturer. Regarding the manufacturer of DBS lead, patients who utilized Abbott (St. Jude) had a significantly longer LOS of 2 days than those who used Medtronic and 1.85 days longer than patients who used Boston Scientific. No other statistically significant relationships were found between the modality of DBS and outcome measures.

Table 4:

Differences in Deep Brain Stimulation Outcomes Based on Surgical Modality.

Table 5:

Differences in deep brain stimulation outcomes based on manufacturer of lead.

DISCUSSION

Our study investigated the impact of sociodemographic factors and surgical modalities on DBS outcomes in PD, utilizing patient LOS and HY scores as outcome measures. When looking at DBS outcomes within a year, our study found no differences in most of our demographic variables, such as race, age, and insurance status. While the efficacy of DBS has been long established, many of our findings do differ from established research that has showcased how social determinants of health significantly impact neurosurgical outcomes, with younger PD patients tending to have better DBS outcomes.[ 11 , 12 , 15 , 17 , 29 , 44 , 50 ] Age has long been an important consideration for DBS candidacy, as aging is associated with declining cognitive status and comorbidities that can increase the risk for surgical complications and are related to a lack of access to DBS.[ 6 , 10 , 38 , 48 ] However, if postoperative complications of DBS are not associated with increasing age, perhaps its usage as a primary exclusion factor for DBS candidacy can be more deeply evaluated.[ 48 ] While proper consideration of all patient factors is essential for DBS candidacy, such findings highlight the importance of recognizing how bias and skewed perception of patient social history could hinder access to treatment and healthcare.

In addition, while marital status has been found to impact surgical outcomes and postoperative functional recovery, few studies have looked at how relationship status affects DBS outcomes.[ 35 ] Our analysis found that divorced patients had a larger MD of HY scores between baseline and 3 months postoperative, showcasing greater improvement compared to other marital groups. These results differ from established findings of how patients recovering from DBS greatly benefit from social support, as they must recover from surgery, take medications accurately and appropriately, regularly visit physicians, and adhere to a complex treatment plan.[ 3 , 21 , 28 ] However, research has showcased that even with substantial motor improvement, DBS can result in increased caregiver burden and marital dissatisfaction.[ 47 ] Despite the benefits of social support, significant role changes and increased familial burden due to the unique complexities of DBS could result in poorer outcomes in the early stages of recovery. While this relationship was not seen between preoperative and 6-month postoperative HY scores, our findings highlight the importance of adequate support and monitoring for patients and their families in the early recovery stages of DBS.

In terms of surgical modalities, the current literature has focused on variables such as anesthesia and implantation location, finding similar effectiveness for GA and LA as well as STN and GPi-DBS implantation in improving motor dysfunction.[ 5 , 9 , 30 , 51 ] This is supported by our lack of significant differences for most of our surgical modalities, such as anesthesia, implantation location, concurrent IPGs, and type of lead.[ 39 ] While directional leads do have advantages and disadvantages, our findings notably differ from the literature that determined how directional leads offer enhanced control and improved motor function and side-effect management.[ 20 , 24 , 25 , 40 ] In addition, DBS settings (i.e., amplitude, pulse width, frequency, and impedance), the activation of directional stimulation, and the use of individualized programs were not examined and could explain the lack of significant findings regarding directional leads. When looking at LEDD, our findings showcased a significant decrease between preoperative and 3-month (P < 0.001) LEDD, preoperative and 6-month (P < 0.001) LEDD, and 3-month and 6-month (P = 0.001) LEDD. While the literature has showcased that DBS can reduce LEDD by 21–65%, research has focused on more long-term effects, looking at changes in medication from 1 year to 15 years. [ 31 , 34 , 45 ] While the effect of our variables on LEDD was not considered, our findings showcase insight into the short-term efficacy of DBS on LEDD and further support the established improvement in the quality of life that DBS can offer.

This is the first study to investigate differences between DBS leads manufactured by Medtronic, Boston Scientific, and Abbott. However, currently, available options for leads and DBS systems also include companies such as Patient Is No. 1 alwayS (PINS) Medical and SceneRay.[ 26 ] Our results showcased that patients who utilized Abbott had a significantly longer LOS of 2 days than Medtronic and 1.85 days longer than Boston Scientific, but no differences were found in terms of HY scores and subsequent motor outcomes. As each manufacturer’s DBS systems have unique attributes such as battery type, programming and software interfaces, and lead design, no recommendations can be made regarding different companies. The type and manufacturer of lead used for each patient are determined through a consideration of different medical indications, patient preferences, and familiarity with the programming platform by relevant movement disorder neurologists. Despite this, our findings warrant a more comprehensive approach to choosing appropriate DBS leads, considering patient comfort and preference as well as maximizing symptom improvement. Future research could spread awareness and education regarding specific nuances and differences between different available manufacturers to both patients and providers. The PD patient population is incredibly large and diverse, and as DBS technology continues to advance, it is essential that physicians consider a patient’s individual and unique needs to determine which modality of DBS would be most beneficial.[ 49 ]

Limitations

This study investigated a comprehensive variety of DBS factors but is not without limitations, as seen with our usage of HY staging as one of our outcome measures. Despite the HY scale being one of the most widely utilized and referenced methods for staging PD severity, HY has been known to suffer from several limiting factors.[ 13 , 18 ] Such f0n actors include ambiguity toward cognitive impairment and disability, as well as being heavily weighted toward motor aspects such as postural instability and mobility issues.[ 42 ] As behavioral and cognitive complications frequently occur during PD and after DBS, HY scores have been primarily superseded by the Unified PD Rating Scale (UPDRS) and revised UPDRS scale by the MDS, known as the MDSUPDRS.[ 16 , 22 ] However, research has found that despite the focus on motor symptoms, HY staging was able to accurately reflect differences in all aspects of PD measured by the MDS-UPDRS, and MDS-UPDRS scores significantly increased with every HY stage.[ 42 ] The lack of differences in our HY scoring could reflect the similarity in motor outcomes for many of our variables. As such, future usage of HY staging, in conjunction with other validated methods of assessing PD, could better determine the comprehensive effect of different modalities of DBS in PD.

Furthermore, sample sizes between our compared groups were occasionally skewed, which could potentially limit the generalizability of our findings. Our patient population was not necessarily representative of larger demographics across the United States, notably lacking any African–American patients. Literature has showcased that demographic and socioeconomic-based disparities affect frequency and access to DBS, with white PD patients being 5 times more likely than African–American PD patients to undergo DBS.[ 4 , 10 , 38 ] Finally, all data were collected from a single institution, resulting in a relatively small sample size of 59 patients. This potentially limits the accuracy and validity of our findings, notably for subgroup analysis. Controlling for these limitations, as well as increasing our sample size and study’s statistical power, could also modulate the lack of significance of race and other modalities of DBS on outcome measures.

CONCLUSION

This study investigated the outcomes of different surgical modalities of DBS in PD patients, as well as the effects of patient sociodemographics, utilizing patient LOS and HY scores as outcome measures. The mean LOS was 2.36 days, the mean HY preoperative score was 3.17, the mean HY 3-month postoperative score was 2.83, and the mean HY 6-month postoperative score was 2.85. LEDD significantly decreased at both 3 and 6 months postoperatively. Divorced patients showcased significantly larger MDs between preoperative and 3-month postoperative HY scores compared to all other relationship groups. Patients who utilized Abbott (St. Jude) had a significantly longer LOS of 2 days than Medtronic and 1.85 days longer than Boston Scientific. No differences in HY scores were found regarding all other variables, including age, race, insurance status, gender, GA versus LA anesthesia, directional versus conventional leads, and lead manufacturer. This study makes no recommendations regarding different companies, but as DBS technology continues to advance, it is essential to consider which modality of DBS would be most beneficial for a growing and diversified patient base.

Ethical approval

The research/study was approved by the Institutional Review Board at Loma Linda University Institutional Review Board, number 5230488, dated November 13, 2023.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent.

Financial support and sponsorship

This research was supported, in part, by the Alpha Omega Alpha Carolyn L. Kuckein Student Research Fellowship. The funding source was not involved in the study design, the collection, analysis, and interpretation of data, the writing of the report, or the decision to submit the article for publication.

Conflicts of interest

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

References

1. Beitz JM. Parkinson’s disease: A review. Front Biosci (Schol Ed). 2014. 6: 65-74

2. Bronstein JM, Tagliati M, Alterman RL, Lozano AM, Volkmann J, Stefani A. Deep brain stimulation for Parkinson disease: An expert consensus and review of key issues. Arch Neurol. 2011. 68: 165

3. Constant E, Brugallé E, Wawrziczny E, Sokolowski C, Manceau C, Flinois B. Relationship dynamics of couples facing advanced-stage Parkinson’s disease: A dyadic interpretative phenomenological analysis. Front Psychol. 2021. 12: 770334

4. Cramer SW, Do TH, Palzer EF, Naik A, Rice AL, Novy SG. Persistent racial disparities in deep brain stimulation for Parkinson’s disease. Ann Neurol. 2022. 92: 246-54

5. DeSouza RM, Moro E, Lang AE, Schapira AH. Timing of deep brain stimulation in Parkinson disease: A need for reappraisal?. Ann Neurol. 2013. 73: 565-75

6. Divo MJ, Martinez CH, Mannino DM. Ageing and the epidemiology of multimorbidity. Eur Respir J. 2014. 44: 1055-68

7. Dorsey ER, Sherer T, Okun MS, Bloem BR. The emerging evidence of the Parkinson pandemic. J Parkinsons Dis. 2018. 8: S3-8

8. Fang JY, Tolleson C. The role of deep brain stimulation in Parkinson’s disease: An overview and update on new developments. Neuropsychiatr Dis Treat. 2017. 13: 723-32

9. França C, Carra RB, Diniz JM, Munhoz RP, Cury RG. Deep brain stimulation in Parkinson’s disease: State of the art and future perspectives. Arq Neuropsiquiatr. 2022. 80: 105-15

10. Frassica M, Kern DS, Afshari M, Connolly AT, Wu C, Rowland N. Racial disparities in access to DBS: Results of a real-world U.S. claims data analysis. Front Neurol. 2023. 14: 1233684

11. Fukaya C, Watanabe M, Kobayashi K, Oshima H, Yoshino A, Yamamoto T. Predictive factors for long-term outcome of subthalamic nucleus deep brain stimulation for Parkinson’s disease. Neurol Med Chir (Tokyo). 2017. 57: 166-71

12. Glauser G, Detchou DK, Dimentberg R, Ramayya AG, Malhotra NR. Social determinants of health and neurosurgical outcomes: Current state and future directions. Neurosurgery. 2021. 88: E383-90

13. Goetz CG, Poewe W, Rascol O, Sampaio C, Stebbins GT, Counsell C. Movement disorder society task force report on the Hoehn and Yahr staging scale: Status and recommendations. Mov Disord. 2004. 19: 1020-8

14. Grant R, Gruenbaum SE, Gerrard J. Anaesthesia for deep brain stimulation: A review. Curr Opin Anaesthesiol. 2015. 28: 505-10

15. Hemming JP, Gruber-Baldini AL, Anderson KE, Fishman PS, Reich SG, Weiner WJ. Racial and socioeconomic disparities in parkinsonism. Arch Neurol. 2011. 68: 498-503

16. Hendricks RM, Khasawneh MT. An investigation into the use and meaning of Parkinson’s disease clinical scale scores. Parkinsons Dis. 2021. 2021: 1765220

17. Hitti FL, Ramayya AG, McShane BJ, Yang AI, Vaughan KA, Baltuch GH. Long-term outcomes following deep brain stimulation for Parkinson’s disease. J Neurosurg. 2020. 132: 205-10

18. Hoehn MM, Yahr MD. Parkinsonism: Onset, progression and mortality. Neurology. 1967. 17: 427-42

19. Holewijn RA, Verbaan D, van den Munckhof PM, Bot M, Geurtsen GJ, Dijk JM. General anesthesia vs local anesthesia in microelectrode recording-guided deep-brain stimulation for parkinson disease: The GALAXY randomized clinical trial. JAMA Neurol. 2021. 78: 1212-9

20. Hurt CP, Kuhman DJ, Moll A, Guthrie BL, Olson JW, Nakhmani A. Pointing in the right direction: Greater motor improvements with directional versus circular subthalamic nucleus deep brain stimulation for Parkinson’s disease. J Parkinson’s Dis. 2024. p.

21. Jankovic J, Tan EK. Parkinson’s disease: Etiopathogenesis and treatment. J Neurol Neurosurg Psychiatry. 2020. 91: 795-808

22. Kahn L, Mathkour M, Lee SX, Gouveia EE, Hanna JA, Garces J. Long-term outcomes of deep brain stimulation in severe Parkinson’s disease utilizing UPDRS III and modified Hoehn and Yahr as a severity scale. Clin Neurol Neurosurg. 2019. 179: 67-73

23. Kalia LV, Lang AE. Parkinson’s disease. Lancet. 2015. 386: 896-912

24. Koivu M, Scheperjans F, Eerola-Rautio J, Vartiainen N, Resendiz-Nieves J, Kivisaari R. Real-life experience on directional deep brain stimulation in patients with advanced Parkinson’s disease. J Pers Med. 2022. 12: 1224

25. Kramme J, Dembek TA, Treuer H, Dafsari HS, Barbe MT, Wirths J. Potentials and limitations of directional deep brain stimulation: A simulation approach. Stereotact Funct Neurosurg. 2021. 99: 65-74

26. Krauss JK, Lipsman N, Aziz T, Boutet A, Brown P, Chang JW. Technology of deep brain stimulation: Current status and future directions. Nat Rev Neurol. 2021. 17: 75-87

27. Krauss P, Duarte-Batista P, Hart MG, Avecillas-Chasin JM, Bercu MM, Hvingelby V. Directional electrodes in deep brain stimulation: Results of a survey by the European Association of Neurosurgical Societies (EANS). Brain Spine. 2024. 4: 102756

28. Kulik JA, Mahler HI. Social support and recovery from surgery. Health Psychol. 1989. 8: 221-38

29. Limousin P, Foltynie T. Long-term outcomes of deep brain stimulation in Parkinson disease. Nat Rev Neurol. 2019. 15: 234-42

30. Liu Z, He S, Li L. General anesthesia versus local anesthesia for deep brain stimulation in Parkinson’s disease: A meta-analysis. Stereotact Funct Neurosurg. 2019. 97: 381-90

31. Mahlknecht P, Foltynie T, Limousin P, Poewe W. How does deep brain stimulation change the course of Parkinson’s disease?. Mov Disord. 2022. 37: 1581-92

32. Moro E, Lang AE. Criteria for deep-brain stimulation in Parkinson’s disease: Review and analysis. Expert Rev Neurother. 2006. 6: 1695-705

33. Munhoz RP, Picillo M, Fox SH, Bruno V, Panisset M, Honey CR. Eligibility criteria for deep brain stimulation in Parkinson’s disease, tremor, and dystonia. Can J Neurol Sci. 2016. 43: 462-71

34. Muthuraman M, Koirala N, Ciolac D, Pintea B, Glaser M, Groppa S. Deep brain stimulation and L-DOPA therapy: Concepts of action and clinical applications in Parkinson’s disease. Front Neurol. 2018. 9: 711

35. Neuman MD, Werner RM. Marital status and postoperative functional recovery. JAMA Surg. 2016. 151: 194-6

36. Ou Z, Pan J, Tang S, Duan D, Yu D, Nong H. Global trends in the incidence, prevalence, and years lived with disability of Parkinson’s disease in 204 countries/territories from 1990 to 2019. Front Public Health. 2021. 9: 776847

37. Paff M, Loh A, Sarica C, Lozano AM, Fasano A. Update on current technologies for deep brain stimulation in Parkinson’s disease. J Mov Disord. 2020. 13: 185-98

38. Sarica C, Conner CR, Yamamoto K, Yang A, Germann J, Lannon MM. Trends and disparities in deep brain stimulation utilization in the United States: A nationwide inpatient sample analysis from 1993 to 2017. Lancet Reg Health Am. 2023. 26: 100599

39. Sarica C, Iorio-Morin C, Aguirre-Padilla DH, Najjar A, Paff M, Fomenko A. Implantable pulse generators for deep brain stimulation: Challenges, complications, and strategies for practicality and longevity. Front Hum Neurosci. 2021. 15: 708481

40. Schüpbach WM, Chabardes S, Matthies C, Pollo C, Steigerwald F, Timmermann L. Directional leads for deep brain stimulation: Opportunities and challenges. Mov Disord. 2017. 32: 1371-5

41. Sharma VD, Patel M, Miocinovic S. Surgical treatment of Parkinson’s disease: Devices and lesion approaches. Neurotherapeutics. 2020. 17: 1525-38

42. Skorvanek M, Martinez-Martin P, Kovacs N, Rodriguez-Violante M, Corvol JC, Taba P. Differences in MDSUPDRS scores based on Hoehn and Yahr stage and disease duration. Mov Disord Clin Pract. 2017. 4: 536-44

43. Steigerwald F, Müller L, Johannes S, Matthies C, Volkmann J. Directional deep brain stimulation of the subthalamic nucleus: A pilot study using a novel neurostimulation device. Mov Disord. 2016. 31: 1240-3

44. Thomas G, Almeida ND, Mast G, Quigley R, Almeida NC, Amdur RL. Racial disparities affecting postoperative outcomes after brain tumor resection. World Neurosurg. 2021. 155: e665-73

45. Thomsen BL, Jensen SR, Clausen A, Karlsborg M, Jespersen B, Løkkegaard A. Deep brain stimulation in Parkinson’s disease: Still effective after more than 8 years. Mov Disord Clin Pract. 2020. 7: 788-96

46. Tomlinson CL, Stowe R, Patel S, Rick C, Gray R, Clarke CE. Systematic review of levodopa dose equivalency reporting in Parkinson’s disease. Mov Disord. 2010. 25: 2649-53

47. Van Hienen MM, Contarino MF, Middelkoop HA, van Hilten JJ, Geraedts VJ. Effect of deep brain stimulation on caregivers of patients with Parkinson’s disease: A systematic review. Parkinsonism Relat Disord. 2020. 81: 20-7

48. Verla T, Marky A, Farber H, Petraglia FW, Gallis J, Lokhnygina Y. Impact of advancing age on post-operative complications of deep brain stimulation surgery for essential tremor. J Clin Neurosci. 2015. 22: 872-6

49. Wright Willis A, Evanoff BA, Lian M, Criswell SR, Racette BA. Geographic and ethnic variation in Parkinson disease: A population-based study of US medicare beneficiaries. Neuroepidemiology. 2010. 34: 143-51

50. Yang Y, Zeitlberger AM, Neidert MC, Staartjes VE, Broggi M, Zattra CM. The association of patient age with postoperative morbidity and mortality following resection of intracranial tumors. Brain Spine. 2021. 1: 100304

51. Zhang J, Li J, Chen F, Liu X, Jiang C, Hu X. STN versus GPi deep brain stimulation for dyskinesia improvement in advanced Parkinson’s disease: A meta-analysis of randomized controlled trials. Clin Neurol Neurosurg. 2021. 201: 106450