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Purpose of Review: The most common four neurodegenerative atypical parkinsonian disorders (APDs) are progressive supranuclear palsy (PSP), multiple system atrophy (MSA), corticobasal syndrome (CBS), and dementia with Lewy bodies (DLB). Their formal diagnostic criteria often require subspecialty experience to implement as designed and all require excluding competing diagnoses without clearly specifying how to do that. Validated diagnostic criteria are not available at all for many of the other common APDs, including normal pressure hydrocephalus (NPH), vascular parkinsonism (VP), or drug-induced parkinsonism (DIP). APDs also include conditions of structural, genetic, vascular, toxic/metabolic, infectious, and autoimmune origin. Their differential diagnosis can be challenging early in the course, if the presentation is atypical, or if a rare or non-neurodegenerative condition is present. This review equips community general neurologists to make an early provisional diagnosis before, or in place of, referral to a tertiary center. Early diagnosis would allay diagnostic uncertainty, allow prompt symptomatic management, provide disease-specific information and support resources, avoid further pointless testing and treatments, and create the possibility of trial referral., Recent Findings: We address 64 APDs using one over-arching flow diagram and a series of detailed tables. Most instances of APDs can be diagnosed with a careful history and neurological exam, along with a non-contrast brain MRI. Additional diagnostic tests are rarely needed but are delineated where applicable. Our diagnostic algorithm encourages referral to a tertiary center whenever the general neurologist feels it would be in the patient's best interest. Our algorithm emphasizes that the diagnosis of APDs is an iterative process, refined with the appearance of new diagnostic features, availability of new technology, and advances in scientific understanding of the disorders. Clinicians' proposals for all diagnostic tests for the APDs, including repeat visits, should be discussed with patients and their families to ensure that the potential information to be gained aligns with their larger clinical goals., Summary: We designed this differential diagnostic algorithm for the APDs to enhance general neurologists' diagnostic skills and confidence and to help them address the less common or more ambiguous cases., Competing Interests: M.K. Bruno: no relevant conflict of interest. She does have research funding from Michael J. Fox Foundation; R. Dhall: no relevant conflict of interest. He has received financial support from the following within the last year: Amneal pharmaceuticals, Sage Therapeutics, Neuroderm, Cerevel Therapeutics, Neurocrine, Neuraly, Alexion, Sun Pharma, Praxis Precision Medicines, Parkinson's Foundation, Aeon Biopharma, Abbvie, Pharma Two B, NIH Parent Grant #UL1TR003107 TRI Pilot Grant “Research Benefitting Rural Populations”. Dr. Dhall has received consulting revenues from Mitsubishi Tanabe Pharma America and Best Doctors. Dr. Dhall reports stock ownership (all at <$10,000) in medically related fields for Armata Pharmaceuticals, Compass Pathways, Biogen Idec, Atea Pharmaceuticals, Gilead Sciences, Imara, Inc, and SQZ Biotech; L.S. Honig: consulted for Biogen Eisai, Genentech/Roche, Medscape, and Prevail/Lilly. L.S. Honig has received research funding from Abbvie, Acumen, Alector, Biogen, Bristol-Myer Squibb, Cognition, Eisai, Genentech/Roche, Janssen/Johnson & Johnson, Eli Lilly, Transposon, UCB, and Vaccinex; Z. Mari: no relevant conflict of interest. He is immediate past Chair of the Movement Disorder Society's Telemedicine Study Group, Director of the Cleveland Clinic Lou Ruvo Center for Brain Health Parkinson's Foundation Center of Excellence, Chair of Parkinson Study Group's Motor Features WG, Associate Editor of Parkinsonism & Related Disorders, president-elect for the Clark County Medical Society, which he also is a Trustee; Z. Mari serves on the IAPRD's Congress Site Selection Committee and Website Committee, and the PPMI's Wearable Devices Task Force. Z. Mari has been recipient of institutional grant support from the NIH, PF, MJFF, Biogen, Eli Lilly, AbbVie, Cerevel, and Praxis Precision Medicines; is cofounder and CMO of Neuraly, Inc, and Z NeuroSciences LLC; is shareholder of D&D PharmaTech, NeuroReserve, Neunos Inc, and Sensory Cloud; and has received honoraria for consulting and advisory board service from GB Sciences, GKC, Bial, Supernus, AbbVie, ACADIA, Sunovion. N.R. McFarland: received research support from the NIH-NINDS, Michael J. Fox Foundation, and Parkinson Foundation. He receives royalties from UpToDate and serves on advisory committee for ONO Pharmaceutical. L. Montaser-Kouhsari received consultant fees from Darmyian, Trinity Life Sciences, Guidepoint, and Techspert, has received research support from the NIH (NINDS), and has received Talk honorarium from Cleveland Clinic. A.M. Wills: no relevant conflict of interest. She does have consulting agreements with Genentech, Amylyx, and Ono pharmaceuticals and have research funding from the NIH, Parkinson's Foundation, and CurePSP. L.I. Golbe: consults for AI Therapeutics, Amylyx, Apellis, Aprinoia, Ferrer, IQVIA, Mitochon, Mitsubishi Tanabe, P3Lab, Roche, Switch, UCB and Woolsey. He serves on advisory boards for Amylyx, CurePSP, Roche, Rossy Centre and Springer. He receives royalties from Rutgers University Press, licensing fees from Rutgers University and travel expenses from CurePSP. The rest of the authors report no relevant conflicts of interest. Full disclosure form information provided by the authors is available with the full text of this article at Neurology.org/cp., (Copyright © 2024 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Neurology.)

Exercise is a well-documented, nonpharmacologic treatment for individuals with autonomic dysfunction and associated orthostatic intolerance, such as postural tachycardia syndrome and related disorders. Exercise has been shown to increase blood volume, reverse cardiovascular deconditioning, and improve quality of life. Current first-line standard of care treatment for autonomic dysfunction combines graded approaches to exercise with medications and lifestyle modifications. However, current exercise rehabilitation protocols for postural orthostatic tachycardia syndrome contain rigid timelines and progression paradigms that often threaten tolerability and adherence. In addition, they fail to account for clinical variables potentially critical to care and lack guidance for individualization, limiting accessibility to patients with co-morbidities that affect exercise appropriateness and safety. Therefore, we introduce an adaptive approach to exercise prescription for orthostatic intolerance that allows patient-specific modifications to meet functional goals for a wider spectrum of patients, thus improving adherence. The proposed approach integrates iterative physiological and symptomatic assessments to provide flexible, yet structured, exposure to aerobic exercise and strength training to improve functional capacity and tolerance of daily activities for patients with postural tachycardia syndrome and related autonomic disorders., Competing Interests: L.Z. has received payment for a Continuing Education Unit course on dysautonomia from the American Physical Therapy Association - Neurologic Specialty Section, financial support for travel related to autonomic presentations. T.C. has received consultation fees from Argenx Pharmaceuticals and Regeneron Pharmaceuticals, and research funding from Dysautonomia International. M.C. has received research funding from the National Institutes of Health National Institute of Neurological Disorders and Stroke (K23NS105920 and R61NS125153; not related to this manuscript) and Dysautonomia International. The other authors have nothing to disclose., (© 2024 The Authors.)

Importance: Finding a reliable diagnostic biomarker for the disorders collectively known as synucleinopathies (Parkinson disease [PD], dementia with Lewy bodies [DLB], multiple system atrophy [MSA], and pure autonomic failure [PAF]) is an urgent unmet need. Immunohistochemical detection of cutaneous phosphorylated α-synuclein may be a sensitive and specific clinical test for the diagnosis of synucleinopathies., Objective: To evaluate the positivity rate of cutaneous α-synuclein deposition in patients with PD, DLB, MSA, and PAF., Design, Setting, and Participants: This blinded, 30-site, cross-sectional study of academic and community-based neurology practices conducted from February 2021 through March 2023 included patients aged 40 to 99 years with a clinical diagnosis of PD, DLB, MSA, or PAF based on clinical consensus criteria and confirmed by an expert review panel and control participants aged 40 to 99 years with no history of examination findings or symptoms suggestive of a synucleinopathy or neurodegenerative disease. All participants completed detailed neurologic examinations and disease-specific questionnaires and underwent skin biopsy for detection of phosphorylated α-synuclein. An expert review panel blinded to pathologic data determined the final participant diagnosis., Exposure: Skin biopsy for detection of phosphorylated α-synuclein., Main Outcomes: Rates of detection of cutaneous α-synuclein in patients with PD, MSA, DLB, and PAF and controls without synucleinopathy., Results: Of 428 enrolled participants, 343 were included in the primary analysis (mean [SD] age, 69.5 [9.1] years; 175 [51.0%] male); 223 met the consensus criteria for a synucleinopathy and 120 met criteria as controls after expert panel review. The proportions of individuals with cutaneous phosphorylated α-synuclein detected by skin biopsy were 92.7% (89 of 96) with PD, 98.2% (54 of 55) with MSA, 96.0% (48 of 50) with DLB, and 100% (22 of 22) with PAF; 3.3% (4 of 120) of controls had cutaneous phosphorylated α-synuclein detected., Conclusions and Relevance: In this cross-sectional study, a high proportion of individuals meeting clinical consensus criteria for PD, DLB, MSA, and PAF had phosphorylated α-synuclein detected by skin biopsy. Further research is needed in unselected clinical populations to externally validate the findings and fully characterize the potential role of skin biopsy detection of phosphorylated α-synuclein in clinical care.

Objectives: To assess the agreement between clinical cardiovascular adrenergic function and cardiac adrenergic innervation in type 2 diabetes patients (T2D)., Methods: Thirty-three patients with T2D were investigated bimodally through (1) a standardized clinical cardiovascular adrenergic assessment, evaluating adequacy of blood pressure responses to the Valsalva maneuver and (2) 123 I-meta-iodobenzylguanidine (MIBG) scintigraphy assessing myocardial adrenergic innervation measured as early and delayed heart heart/mediastinum (H/M) ratio, and washout rate (WR)., Results: T2D patients had significantly lower early and delayed H/M-ratios, and lower WR, compared to laboratory specific reference values. Thirteen patients had an abnormal adrenergic composite autonomic severity score (CASS > 0). Patients with abnormal CASS scores had significantly higher early H/M ratios (1.76 [1.66-1.88] vs. 1.57 [1.49-1.63], p < 0.001), higher delayed H/M ratios (1.64 [1.51:1.73] vs. 1.51 [1.40:1.61] (p = 0.02)), and lower WR (-0.13(0.10) vs -0.05(0.07), p = 0.01). Lower Total Recovery and shorter Pressure Recovery Time responses from the Valsalva maneuver was significantly correlated to lower H/M early (r = 0.55, p = 0.001 and r = 0.5, p = 0.003, respectively) and lower WR for Total Recovery (r = -0.44, p = 0.01)., Conclusion: The present study found impairment of sympathetic innervation in T2D patients based on parameters derived from MIBG cardiac scintigraphy (low early H/M, delayed H/M, and WR). These results confirm prior studies. We found a mechanistically inverted relationship with favourable adrenergic cardiovascular responses being significantly associated unfavourable MIBG indices for H/M early and delayed. This paradoxical relationship needs to be further explored but could indicate adrenergic hypersensitivity in cardiac sympathetic denervated T2D patients., Competing Interests: Declaration of competing interest We report no potential conflicts of interest in relation to this manuscript., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Purpose: We investigated the effect of levodopa on postural blood pressure changes in individuals with Parkinson disease (PD) with (PD +OH ) and without neurogenic OH (PD -OH )., Methods: We performed a prospective randomized crossover study with autonomic testing performed ON and OFF levodopa. The primary outcome was the change in systolic blood pressure (SBP) from supine to 70° tilt at 3 min (ΔSBP-3'). Secondary outcomes included indices of baroreflex function and blood pressure and heart rate during tilt., Results: We enrolled 40 individuals with PD (21 PD +OH , 19 PD -OH ), mean age (SD) 73.2 years (7.9), 13 women (32.5%)). There was no difference in age, sex, disease duration, and severity between PD +OH and PD -OH . Mean difference in ΔSBP-3' ON versus OFF levodopa in the whole study population was - 3.20 mmHg [- 7.36 to 0.96] (p = 0.14). Mean difference in ΔSBP-3' was - 2.14 mmHg [- 7.55 to 3.28] (p = 0.45) in PD +OH and - 5.14 mmHg [- 11.63 to 1.35] (p = 0.14) in PD -OH . Mean difference in ΔSBP ON versus OFF levodopa was greater at 7 and 10 min (- 7.52 mmHg [- 11.89 to - 3.15], p = 0.002, and - 7.82 mmHg [- 14.02 to - 1.67], p = 0.02 respectively). Levodopa was associated with lower absolute values of blood pressure in both PD +OH and PD -OH and cardiovascular noradrenergic baroreflex impairment., Conclusion: Levodopa decreases blood pressure in both PD with and without autonomic failure, but it does not cause a greater fall in blood pressure from supine to standing at 3 min. Levodopa-induced baroreflex sympathetic noradrenergic impairment may contribute to lower blood pressure. Lower standing blood pressure with levodopa may increase the risks of fall and syncope., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany.)

There is compelling evidence that exercise must be part of main line therapy for people with Parkinson's disease. In this viewpoint, we outline the four key components of exercise: aerobic exercise, resistance exercise, flexibility exercise, and neuromotor exercises (posture, gait, balance, and agility) that can improve both motor and non-motor symptoms of the disease and, in the case of aerobic exercise, may delay the disease. We outline guidelines on how to change and optimize the exercise prescription at different stages of the disease.

Background: An attenuated heart rate response to exercise, termed chronotropic incompetence, has been reported in Parkinson's disease (PD). Chronotropic incompetence may be a marker of autonomic dysfunction and a cause of exercise intolerance in early stages of PD., Objective: To investigate the relationship between chronotropic incompetence, orthostatic blood pressure change (supine - standing), and exercise performance (maximal oxygen consumption, VO2peak) in individuals with early PD within 5 years of diagnosis not on dopaminergic medications., Methods: We performed secondary analyses of heart rate and blood pressure data from the Study in Parkinson's Disease of Exercise (SPARX)., Results: 128 individuals were enrolled into SPARX (63.7±9.3 years; 57.0% male, 0.4 years since diagnosis [median]). 103 individuals were not taking chronotropic medications, of which 90 had a normal maximal heart rate response to exercise testing (155.3±14.0 bpm; PDnon-chrono) and 13 showed evidence of chronotropic incompetence (121.3±11.3 bpm; PDchrono, p < 0.05). PDchrono had decreased VO2peak compared to PDnon-chrono (19.7±4.5 mL/kg/min and 24.3±5.8 mL/kg/min, respectively, p = 0.027). There was a positive correlation between peak heart rate during exercise and the change in systolic blood pressure from supine to standing (r = 0.365, p < 0.001)., Conclusions: A subgroup of individuals with early PD not on dopaminergic medication had chronotropic incompetence and decreased VO2peak, which may be related to autonomic dysfunction. Evaluation of both heart rate responses to incremental exercise and orthostatic vital signs may serve as biomarkers of early autonomic impairment and guide treatment. Further studies should investigate whether cardiovascular autonomic dysfunction affects the ability to exercise and whether exercise training improves autonomic dysfunction.

Orthostatic hypotension (OH) is the most common manifestation of cardiovascular autonomic dysfunction in Parkinson's disease. In this viewpoint, we discuss five practical questions regarding OH in Parkinson's disease: 1) How common is the problem? 2) Why should people with Parkinson's disease and providers care about OH? 3) What are the symptoms of OH? 4) How to confirm a diagnosis of OH? And 5) How to treat OH? OH is an important non-motor symptom of Parkinson's disease for which we have available treatments to significantly mitigate morbidity and possibly positively impact the disease course.

The α-synucleinopathies include pure autonomic failure, multiple system atrophy, dementia with Lewy bodies, and Parkinson disease. The past two decades have witnessed significant advances in the diagnostic strategies and symptomatic treatment of motor and nonmotor symptoms of the synucleinopathies. This chapter provides an in-depth review of the pathophysiology, pathology, genetic, epidemiology, and clinical and laboratory autonomic features that distinguish the different synucleinopathies with an emphasis on autonomic failure as a common feature. The treatment of the different synucleinopathies is discussed along with the proposal for multidisciplinary, individualized care models that optimally address the various symptoms. There is an urgent need for clinical scientific studies addressing patients at risk of developing synucleinopathies and the investigation of disease mechanisms, biomarkers, potential disease-modifying therapies, and further advancement of symptomatic treatments for motor and nonmotor symptoms., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Purpose of Review: Autonomic neuropathies are a complex group of disorders and result in diverse clinical manifestations that affect the cardiovascular, gastrointestinal, urogenital, and sudomotor systems. We focus this review on the diagnosis and treatment of peripheral autonomic neuropathies. We summarize the diagnostic tools and current treatment options that will help the clinician care for individuals with peripheral autonomic neuropathies., Recent Findings: Autonomic neuropathies occur often in conjunction with somatic neuropathies but they can also occur in isolation. The autonomic reflex screen is a validated tool to assess sympathetic postganglionic sudomotor, cardiovascular sympathetic noradrenergic, and cardiac parasympathetic (i.e., cardiovagal) function. Initial laboratory evaluation for autonomic neuropathies includes fasting glucose or oral glucose tolerance test, thyroid function tests, kidney function tests, vitamin-B12, serum, and urine protein electrophoresis with immunofixation. Other laboratory tests should be guided by the clinical context. Reduced intraepidermal nerve density on skin biopsy is a finding, not a diagnosis. Skin biopsy can be helpful in selected individuals for the diagnosis of disorders affecting small nerve fibers; however, we strongly discourage the use of skin biopsy without clinical-physiological correlation. Ambulatory blood pressure monitoring may lead to early identification of patients with cardiovascular autonomic neuropathy in the primary care setting. Disease-modifying therapies should be used when available in combination with nonpharmacological management and symptomatic pharmacologic therapies. Autonomic function testing can guide the therapeutic decisions and document improvement with treatment. A systematic approach guided by the autonomic history and standardized autonomic function testing may help clinicians when identifying and/or counseling patients with autonomic neuropathies. Treatment should be individualized and disease-modifying therapies should be used when available., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Background: To date, no medication has slowed the progression of Parkinson's disease (PD). Preclinical, epidemiological, and experimental data on humans all support many benefits of endurance exercise among persons with PD. The key question is whether there is a definitive additional benefit of exercising at high intensity, in terms of slowing disease progression, beyond the well-documented benefit of endurance training on a treadmill for fitness, gait, and functional mobility. This study will determine the efficacy of high-intensity endurance exercise as first-line therapy for persons diagnosed with PD within 3 years, and untreated with symptomatic therapy at baseline., Methods: This is a multicenter, randomized, evaluator-blinded study of endurance exercise training. The exercise intervention will be delivered by treadmill at 2 doses over 18 months: moderate intensity (4 days/week for 30 min per session at 60-65% maximum heart rate) and high intensity (4 days/week for 30 min per session at 80-85% maximum heart rate). We will randomize 370 participants and follow them at multiple time points for 24 months. The primary outcome is the Movement Disorders Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) motor score (Part III) with the primary analysis assessing the change in MDS-UPDRS motor score (Part III) over 12 months, or until initiation of symptomatic antiparkinsonian treatment if before 12 months. Secondary outcomes are striatal dopamine transporter binding, 6-min walk distance, number of daily steps, cognitive function, physical fitness, quality of life, time to initiate dopaminergic medication, circulating levels of C-reactive protein (CRP), and brain-derived neurotrophic factor (BDNF). Tertiary outcomes are walking stride length and turning velocity., Discussion: SPARX3 is a Phase 3 clinical trial designed to determine the efficacy of high-intensity, endurance treadmill exercise to slow the progression of PD as measured by the MDS-UPDRS motor score. Establishing whether high-intensity endurance treadmill exercise can slow the progression of PD would mark a significant breakthrough in treating PD. It would have a meaningful impact on the quality of life of people with PD, their caregivers and public health., Trial Registration: ClinicalTrials.gov NCT04284436 . Registered on February 25, 2020., (© 2022. The Author(s).)

Purpose of the Review: Orthostatic hypotension (OH) is the primary manifestation of cardiovascular autonomic dysfunction in Parkinson disease (PD) and can be a prodromal feature of the disease. We review the recent progress in the field of autonomic dysfunction in PD., Recent Findings: Individuals with isolated neurogenic OH should be followed up frequently because they may evolve into PD, dementia with Lewy bodies, or multiple system atrophy. The prevalence of OH in PD increases with disease stages, but the role of levodopa remains unclear. Measurement of supine and standing heart rate and blood pressure allows for accurate identification of neurogenic OH in the clinic., Summary: Accurate identification of neurogenic OH in the clinic is crucial for identification of individuals who may benefit from participation in neuroprotective trials in the future. The treatment of OH in PD should be individualized and may reduce the risk of falls, cognitive impairment, and death., (© 2022 American Academy of Neurology.)

Background: It remains elusive how the characteristics, the course of disease, the clinical management and the outcomes of critically ill COVID-19 patients admitted to intensive care units (ICU) worldwide have changed over the course of the pandemic., Methods: Prospective, observational registry constituted by 90 ICUs across 22 countries worldwide including patients with a laboratory-confirmed, critical presentation of COVID-19 requiring advanced organ support. Hierarchical, generalized linear mixed-effect models accounting for hospital and country variability were employed to analyse the continuous evolution of the studied variables over the pandemic., Results: Four thousand forty-one patients were included from March 2020 to September 2021. Over this period, the age of the admitted patients (62 [95% CI 60-63] years vs 64 [62-66] years, p < 0.001) and the severity of organ dysfunction at ICU admission decreased (Sequential Organ Failure Assessment 8.2 [7.6-9.0] vs 5.8 [5.3-6.4], p < 0.001) and increased, while more female patients (26 [23-29]% vs 41 [35-48]%, p < 0.001) were admitted. The time span between symptom onset and hospitalization as well as ICU admission became longer later in the pandemic (6.7 [6.2-7.2| days vs 9.7 [8.9-10.5] days, p < 0.001). The PaO 2 /FiO 2 at admission was lower (132 [123-141] mmHg vs 101 [91-113] mmHg, p < 0.001) but showed faster improvements over the initial 5 days of ICU stay in late 2021 compared to early 2020 (34 [20-48] mmHg vs 70 [41-100] mmHg, p = 0.05). The number of patients treated with steroids and tocilizumab increased, while the use of therapeutic anticoagulation presented an inverse U-shaped behaviour over the course of the pandemic. The proportion of patients treated with high-flow oxygen (5 [4-7]% vs 20 [14-29], p < 0.001) and non-invasive mechanical ventilation (14 [11-18]% vs 24 [17-33]%, p < 0.001) throughout the pandemic increased concomitant to a decrease in invasive mechanical ventilation (82 [76-86]% vs 74 [64-82]%, p < 0.001). The ICU mortality (23 [19-26]% vs 17 [12-25]%, p < 0.001) and length of stay (14 [13-16] days vs 11 [10-13] days, p < 0.001) decreased over 19 months of the pandemic., Conclusion: Characteristics and disease course of critically ill COVID-19 patients have continuously evolved, concomitant to the clinical management, throughout the pandemic leading to a younger, less severely ill ICU population with distinctly different clinical, pulmonary and inflammatory presentations than at the onset of the pandemic., (© 2022. The Author(s).)

Introduction: Levodopa is the most effective medication for the treatment of motor symptoms of Parkinson's disease (PD). Several factors may affect the efficacy and tolerability of levodopa. These include the timing, dosage and administration of levodopa, concomitant drugs, food, PD-associated non-motor symptoms, and various neurologic and non-neurologic comorbidities. If not appropriately addressed, these issues may limit levodopa efficacy, tolerability, and compliance., Areas Covered: This article reviews the basics of the metabolism of orally administered levodopa, its side effects, and the factors that may affect its tolerability and efficacy. We provide several practical pearls to improve the tolerability and efficacy of levodopa., Expert Opinion: Protein-rich food delays and reduces levodopa absorption. Hence, levodopa should preferably be administered in a relatively empty stomach. Carbidopa dosing is crucial as it not only enhances the entry of levodopa into the central nervous system but also reduces levodopa's peripheral adverse effects. Patients experiencing the early side effects such as nausea/vomiting should be prescribed with anti-nausea medications that do not block dopamine receptors. Non-oral routes of administration can be used to obviate persistent gastrointestinal side effects. Implementation of these and other tips may help improve the tolerability and efficacy of levodopa.