Longitudinal study of levodopa in Parkinson's disease: effects of the advanced disease phase

Parkinsonian Tremor as Unstable Feedback in a Physiologically Consistent Control Framework

Parkinson's disease (PD) is characterized by decreased dopamine in the basal ganglia that causes excessive tonic inhibition of the thalamus. This excessive inhibition seems to explain inhibitory motor symptoms in PD, but the source of tremor remains unclear. This paper investigates how neural inhibition may change the closed-loop characteristics of the human motor control system to determine how this established pathophysiology could produce tremor. The rate-coding model of neural signals suggests increased inhibition decreases signal amplitude, which could create a mismatch between the closed-loop dynamics and the internal models that overcome proprioceptive feedback delays. This paper aims to identify a candidate model structure with decreased-amplitude-induced tremor in PD that also agrees with previously recorded movements of healthy and cerebellar patients. The optimal feedback control theory of human motor control forms the basis of the model. Key additional elements include gating of undesired movements via the basal ganglia-thalamus-motor cortex circuit and the treatment of the efferent copy of the control input as a measurement in the state estimator. Simulations confirm the model's ability to capture tremor in PD and also demonstrate how disease progression could affect tremor and other motor symptoms, providing insight into the existence of tremor and non-tremor phenotypes. Altogether, the physiological underpinnings of the model structure and the agreement of model predictions with clinical observations provides support for the hypothesis that unstable feedback produces parkinsonian tremor. Consequently, these results also support the associated framework for the neuroanatomy of human motor control.

The effect of dopamine replacement therapy on cortical structure in Parkinson's disease

AIMS

To explore the cortical structural reorganization in Parkinson's disease (PD) patients under chronic dopamine replacement therapy (DRT) in cross-sectional and longitudinal data and determine whether these changes were associated with clinical alterations.

METHODS

A total of 61 DRT-treated, 60 untreated PD patients, and 61 normal controls (NC) were retrospectively included. Structural MRI scans and neuropsychological tests were conducted. Cortical thickness and volume were extracted based on FreeSurfer and were analyzed using general linear model to find statistically significant differences among three groups. Correlation analyses were performed among significant cortical areas, medication treatment (duration and dosage), and neuropsychological tests. Longitudinal cortical structural changes of patients who initiated DRT were analyzed using linear mixed-effect model.

RESULTS

Significant cortical atrophy was primarily observed in the prefrontal cortex in treated patients, including the cortical thickness of right pars opercularis and the volume of bilateral superior frontal cortex (SFC), left rostral anterior cingulate cortex (rACC), right lateral orbital frontal cortex, right pars orbitalis, and right rostral middle frontal cortex. A negative correlation was detected between the left SFC volume and levodopa equivalent dose (LED) (r = -0.316, p = 0.016), as well as the left rACC volume and medication duration (r = -0.329, p = 0.013). In the patient group, the left SFC volume was positively associated with digit span forward score (r = 0.335, p = 0.017). The left SFC volume reduction was longitudinally correlated with increased LED (standardized coefficient = -0.077, p = 0.001).

CONCLUSION

This finding provided insights into the influence of DRT on cortical structure and highlighted the importance of drug dose titration in DRT.

Anticipatory Postural Adjustments and Compensatory Postural Responses to Multidirectional Perturbations-Effects of Medication and Subthalamic Nucleus Deep Brain Stimulation in Parkinson's Disease

BACKGROUND

Postural instability is one of the most restricting motor symptoms for patients with Parkinson's disease (PD). While medication therapy only shows minor effects, it is still unclear whether medication in conjunction with deep brain stimulation (DBS) of the subthalamic nucleus (STN) improves postural stability. Hence, the aim of this study was to investigate whether PD patients treated with medication in conjunction with STN-DBS have superior postural control compared to patients treated with medication alone.

METHODS

Three study groups were tested: PD patients on medication (PD-MED), PD patients on medication and on STN-DBS (PD-MED-DBS), and healthy elderly subjects (HS) as a reference. Postural performance, including anticipatory postural adjustments (APA) prior to perturbation onset and compensatory postural responses (CPR) following multidirectional horizontal perturbations, was analyzed using force plate and electromyography data.

RESULTS

Regardless of the treatment condition, both patient groups showed inadequate APA and CPR with early and pronounced antagonistic muscle co-contractions compared to healthy elderly subjects. Comparing the treatment conditions, study group PD-MED-DBS only showed minor advantages over group PD-MED. In particular, group PD-MED-DBS showed faster postural reflexes and tended to have more physiological co-contraction ratios.

CONCLUSION

medication in conjunction with STN-DBS may have positive effects on the timing and amplitude of postural control.

Putaminal y-Aminobutyric Acid Modulates Motor Response to Dopaminergic Therapy in Parkinson's Disease

BACKGROUND

Motor response to dopaminergic therapy is a characteristic of patients with Parkinson's disease (PD). Whether nondopaminergic neurotransmitters contribute to treatment response is uncertain.

OBJECTIVES

The aim of this study is to determine whether putaminal y-aminobutyric acid (GABA) levels are associated with dopaminergic motor response.

METHODS

We assessed putaminal GABA levels in 19 PD patients and 13 healthy controls (HCs) utilizing ultra-high field proton magnetic resonance spectroscopy. Motor performance was evaluated using the Movement Disorder Society-Unified Parkinson's Disease Rating Scale, Part III, in the ON and OFF states. Statistical analysis comprised group comparisons, correlation analysis, and multiple linear regression.

RESULTS

In PD, GABA levels were significantly higher compared to HCs (1.50 ± 0.26 mM vs. 1.26 ± 0.31 mM, P = 0.022). Furthermore, GABA levels were independent predictors of absolute and relative dopaminergic treatment response.

CONCLUSIONS

Our findings indicate that elevated putaminal GABA levels are associated with worse dopaminergic response in PD, emphasizing the essential role of nondopaminergic neurotransmitters in motor response. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Prediction of the Levodopa Challenge Test in Parkinson's Disease Using Data from a Wrist-Worn Sensor

The response to levodopa (LR) is important for managing Parkinson’s Disease and is measured with clinical scales prior to (OFF) and after (ON) levodopa. The aim of this study was to ascertain whether an ambulatory wearable device could predict the LR from the response to the first morning dose. The ON and OFF scores were sorted into six categories of severity so that separating Parkinson’s Kinetigraph (PKG) features corresponding to the ON and OFF scores became a multi-class classification problem according to whether they fell below or above the threshold for each class. Candidate features were extracted from the PKG data and matched to the class labels. Several linear and non-linear candidate statistical models were examined and compared to classify the six categories of severity. The resulting model predicted a clinically significant LR with an area under the receiver operator curve of 0.92. This study shows that ambulatory data could be used to identify a clinically significant response to levodopa. This study has also identified practical steps that would enhance the reliability of this test in future studies.

Dysphagia predicts poor outcome in late-stage Parkinson's disease

BACKGROUND

Few data exist on the rate of clinical progression for Parkinson's disease (PD) patients who have entered a late stage of the disease.

OBJECTIVE

Study the clinical progression of a late-stage PD (LSPD) population over one year follow-up.

METHODS

50 LSPD patients (Schwab and England ADL Scale <50 or Hoehn Yahr Stage >3 in MED ON) underwent an extensive clinical assessment at baseline and after one year and an acute levodopa test at baseline.

RESULTS

Mean age of LSPD patients (female 46%) was 77.5 ± 5.9 years and mean disease duration was 15.5 ± 6.5 years. At baseline, 76% had levodopa-induced motor complications (MC), usually non-troublesome, 68% were demented, 54% had psychosis and 68% depression. Caregiver distress was high. l-dopa responsiveness was mild (18% ± 12 of improvement on MDS-UPDRS-III). After one-year, 20% of the patients were dead, institutionalized or HY 5. MDS-UPDRS-motor mean score worsened 7.2 ± 10.3 points although there was heterogeneity between patients, and there was a global worsening of non-motor symptoms, mostly in cognition/mood, urinary and gastrointestinal domains. Nevertheless, MC improved despite similar levodopa equivalent dose. Functional independence and quality of life worsened. Dysphagia severity at baseline predicted a poor outcome (death, institutionalization or HY 5) (Hazard ratio 2.3, 95% CI 1.12-4.4; p = 0.01), whereas magnitude of l-dopa response of LSPD patients did not.

CONCLUSIONS

LSPD patients still present a significant, although heterogeneous, motor and non-motor progression over 1 year. Dysphagia severity predicts the occurrence of additional disease severity milestones and its management must be prioritized.

Inferring the long duration response to levodopa in Parkinson's disease

INTRODUCTION

The long duration response to levodopa in Parkinson's disease outlasts drug elimination by days to weeks. Though a substantive part of anti-parkinsonian motor benefit, it cannot easily be observed.

OBJECTIVES

To infer the magnitude of the long duration response during the first decade of Parkinson's disease and identify factors that influence it.

METHODS

Serial practically defined off scores of 24 patients from a longitudinal study of levodopa short duration response were used to establish their rate of motor progression. A line of notional untreated disability (as if drug treatment had never been given) with the same progression gradient was the basis for calculation of the long duration response. Predictors of mean long duration response amplitude were identified using a multiple linear regression model.

RESULTS

Over a mean treatment period of 16.6 ± 4.4 years, annual increase in motor disability was 2.3% of the maximum score. The long duration response composed 49% of total levodopa response during the first decade of treatment, and this proportion was significantly higher soon after commencing levodopa (p = 0.001). Higher pre-treatment motor score (r = 0.60) and lower MMSE (r = 0.60) were the main predictors of a larger long duration response. There was little correlation between long and short duration responses.

CONCLUSIONS

Long duration responses contribute almost half of the total levodopa benefit during the first decade of treatment. An appreciation of both long and short duration components of drug symptomatic effects is important in clinical trial design to investigate possible neuroprotective treatments.

Method of Levodopa Response Calculation Determines Strength of Association With Clinical Factors in Parkinson Disease

Background

The levodopa challenge test is routinely used in Parkinson disease (PD) to determine a patient’s motor improvement following levodopa administration [levodopa response (LR)]. LR is most commonly reported as a percent OFF to ON change in the Unified Parkinson Disease Rating Scale (UPDRS) part III score, and occasionally as an absolute difference in score. This inconsistency in LR determination alters how clinical factors such as patient age and disease duration are understood in relation to LR in PD.

Objective

The aim of this study was to compare the calculation of the LR as either a percent change or difference in UPDRS-III motor score between OFF and ON medication. These two scores were then used to correlate to disease duration, patient age, levodopa duration, levodopa equivalent dose (LED), OFF score, cognition, mood, gait, and quality of life (QOL).

Methods

70 PD patients underwent the levodopa challenge test. The UPDRS-III motor examination was performed in the defined OFF and ON medication states to determine LR. Each patient was assessed after 12–14 h without anti-parkinsonian medication and then given three 100/25 mg levodopa/carbidopa tablets. LR was reported as both a difference in score [OFF − ON; absolute LR (aLR)] and as a percent change in score [(OFF − ON)/OFF*100%; %LR]. Patients completed the following non-motor symptom assessment scales: Montreal Cognitive Assessment, Freezing of Gait Questionnaire, Activities-specific Balance Confidence Scale, Parkinson’s Disease Questionnaire, and Geriatric Depression Scale. The effect of the LR calculation method was correlated to the clinical measures.

Results

The aLR was significantly associated with disease duration (r = 0.40), levodopa duration (r = 0.47), OFF motor score (r = 0.58), and LED (r = 0.31), but not age. The aLR was also found to have a significant relationship with clinical scales assessing cognition (r = 0.41), freezing of gait (r = 0.35), QOL (r = 0.40), and depression (r = 0.30). By contrast, the more commonly used %LR demonstrated no significant relationships with any of the variables tested.

Conclusion

Although the %LR is more commonly employed in clinical protocols and research studies, the aLR is the superior method for reporting motor response to levodopa in PD given its significant associations with the clinical factors evaluated.

Treatment of Advanced Parkinson Disease and Related Disorders

PURPOSE OF REVIEW

Parkinson disease often spans decades of a patient's lifetime. Over time, nonmotor symptoms predominate and may limit dopaminergic therapy. Neurologists continue to play a vital role in treatment. In addition to balancing neurobehavioral complications of Parkinson disease with motor benefit, addressing nonmotor symptoms common in the advanced stage may improve quality of life and reduce symptom burden. Symptoms such as dysphagia, constipation, urinary dysfunction, orthostatic hypotension, and pain respond to nonpharmacologic and pharmacologic therapies.

RECENT FINDINGS

Evidence for treatment of many nonmotor symptoms is weak or lacking. The evidence for treatment of the atypical parkinsonian syndromes (progressive supranuclear palsy, multiple system atrophy, and corticobasal degeneration) in advanced stages is even more scant.

SUMMARY

Engaging palliative care physicians in the joint care of patients can provide patients with access to expertise in end-of-life issues. Neurologic illnesses have specific hospice criteria to guide clinicians for referrals. Evidence supports that assisting patients with advance directives can result in improved satisfaction with care and improved quality of life in the last weeks of life. Neurologists can remain engaged in their patients' care throughout the course of illness.

Effect of Age and Disease Duration on the Levodopa Response in Patients with Advanced Parkinson's Disease for Deep Brain Stimulation of the Subthalamic Nucleus

Background

Deep brain stimulation (DBS) has become a preferred option for the treatment of motor symptoms in patients with advanced Parkinson’s disease (PD). A good levodopa response (LR) is considered the most important criterion in determining the suitability of a patient for DBS. However, the effect of age and disease duration (DD) on the LR is still a subject of discussion.

Objective

Here, we investigated the effect of age and DD on the preoperative LR in PD patients to be selected for DBS.

Methods

From August 2011 to May 2015, 54 consecutive patients (29 men and 25 women) with advanced PD were evaluated for DBS of the STN and included in this retrospective study.

Results

Thirty-seven patients were found suitable for DBS of the STN and 29 of them underwent bilateral surgery. We found no significant correlation between DD and the LR. However, there was a significant negative correlation between the patients’ age and the LR.

Conclusion

The results indicate that the patients’ age, rather than DD, has a negative effect on the LR. The study, therefore, indicates that PD patients with an advanced age and with a poor LR are not good candidates for DBS of the STN.

Predictors of cognitive impairment in an early stage Parkinson's disease cohort

The impact of Parkinson’s disease (PD) dementia is substantial and has major functional and socioeconomic consequences. Early prediction of future cognitive impairment would help target future interventions. The Montreal Cognitive Assessment (MoCA), the Mini-Mental State Examination (MMSE), and fluency tests were administered to 486 patients with PD within 3.5 years of diagnosis, and the results were compared with those from 141 controls correcting for age, sex, and educational years. Eighteen-month longitudinal assessments were performed in 155 patients with PD. The proportion of patients classified with normal cognition, mild cognitive impairment (MCI), and dementia varied considerably, depending on the MoCA and MMSE thresholds used. With the MoCA total score at screening threshold, 47.7%, 40.5%, and 11.7% of patients with PD were classified with normal cognition, MCI, and dementia, respectively; by comparison, 78.7% and 21.3% of controls had normal cognition and MCI, respectively. Cognitive impairment was predicted by lower education, increased age, male sex, and quantitative motor and non-motor (smell, depression, and anxiety) measures. Longitudinal data from 155 patients with PD over 18 months showed significant reductions in MoCA scores, but not in MMSE scores, with 21.3% of patients moving from normal cognition to MCI and 4.5% moving from MCI to dementia, although 13.5% moved from MCI to normal; however, none of the patients with dementia changed their classification. The MoCA may be more sensitive than the MMSE in detecting early baseline and longitudinal cognitive impairment in PD, because it identified 25.8% of those who experienced significant cognitive decline over 18 months. Cognitive decline was associated with worse motor and non-motor features, suggesting that this reflects a faster progressive phenotype.