Dyskinesias and levodopa therapy: why wait?

Does Delaying Levodopa Prevent Motor Complications in Parkinson's Disease? A Meta-Analysis

BACKGROUND

There has been a long debate whether delaying treatment with levodopa prevents motor complications in Parkinson's disease (PD).

OBJECTIVES

We performed a meta-analysis on randomized clinical trials (RCTs) that compared early- versus delayed-start treatment with levodopa in PD.

METHODS

A systematic review was conducted in PubMed, EMBASE, and Web of Science databases from inception to July 1, 2023. Only RCTs that compared early and delayed levodopa treatment in PD were included. Non-randomized comparisons from follow-up studies were included as well. Our primary outcomes were occurrence of overall motor complications, motor fluctuations, and dyskinesias.

RESULTS

Seven studies with a total of 1149 patients (636 in the early-start group and 513 in the delayed-start) were included in our analysis. There was no difference between groups regarding motor complications (OR 1.39; 95% CI: 0.68-1.72; P = 0.37) or dyskinesias (OR 1.52; 95% CI: 0.90-2.57; P = 0.11). Motor fluctuations occurred less frequently in the early-start group (OR 0.70; 95% CI: 0.52-0.95; P = 0.02). Nonetheless, on subgroup analysis of dopamine agonists, rate of dyskinesias was smaller in the delayed-start group (OR 1.82; 95% CI: 1.08-3.07; P = 0.03).

CONCLUSIONS

Delaying treatment with levodopa does not seem to prevent levodopa-related motor complications in PD. Adjunct treatment with dopamine agonists may reduce the need for higher doses of levodopa and thus reduce the risk for dyskinesias but this practice is often associated with a higher frequency of adverse effects related to dopamine agonists.

Tailoring Motor Fluctuation Treatment: Beyond Levodopa Dose Adjustment

Susan Fox opened this satellite symposium at the 8th European Academy of Neurology (EAN) Congress with an overview of the concept of motor fluctuations (MF) in Parkinson’s disease (PD). She emphasised that levodopa remains the gold standard therapy for PD. However, MFs are one of the critical complications of levodopa therapy that affect many patients with advancing PD and, when diagnosed, represent a challenge in patient management. Alternative options are, therefore, needed to provide continuous dopaminergic stimulation while maximising the levodopa benefit. Despite different options, Angelo Antonini showed that neurologists often prefer to adjust levodopa dose rather than add an adjunctive agent. Market research confirms that, in patients with PD, the levodopa dose is adjusted in around 80% of patients, while only 20% have adjunct therapy as a first-line option. Adjusting the levodopa dose, either by increasing or fractionating the dose, or both, remains a valid, tried-and-tested option, although it has limitations. Joaquim Ferreira presented emerging evidence from a Phase II clinical trial, suggesting a potential benefit of adding opicapone 50 mg compared with 100 mg levodopa to treat patients with PD and end-of-dose fluctuations. This symposium aimed to present the effect of opicapone with relatively low total daily doses of levodopa; an option that may not have been traditionally considered by neurologists who are used to adjusting levodopa as a first-line response.

Nigral Iron Deposition Is Associated With Levodopa-Induced Dyskinesia in Parkinson's Disease

Objective

To investigate iron deposition in the substantia nigra (SN) of Parkinson’s disease (PD) patients associated with levodopa-induced dyskinesia (LID).

Methods

Seventeen PD patients with LID, 17 PD patients without LID, and 16 healthy controls were recruited for this study. The mean QSM values of the whole, left, and right SN were compared among the three groups. A multivariate logistic regression model was constructed to determine the factors associated with increased risk of LID. The receiver operating characteristic curve of the QSM value of SN in discriminating PD with and without LID was evaluated.

Results

The mean QSM values of the whole and right SN in the PD with LID were higher than those in the PD without LID (^∗P = 0.03, ^∗P = 0.03). Multivariate logistic regression analysis revealed that the QSM value of whole, left, or right SN was a predictor of the development of LID (^∗P = 0.03, ^∗P = 0.04, and ^∗P = 0.04). The predictive accuracy of LID in adding the QSM value of the whole, left, and right SN to LID-related clinical risk factors was 70.6, 64.7, and 67.6%, respectively. The QSM cutoff values between PD with and without LID of the whole, left, and right SN were 148.3, 165.4, and 152.7 ppb, respectively.

Conclusion

This study provides the evidence of higher iron deposition in the SN of PD patients with LID than those without LID, suggesting that the QSM value of the SN may be a potential early diagnostic neuroimaging biomarker for LID.

The increased gray matter volumes of precentral gyri in Parkinson's disease patients with diphasic dyskinesia

Abnormal dopaminergic modulation of the cortico-basal ganglia motor loops results in the emergence of levodopa-induced dyskinesia (LID). We focused on alterations in the gray matter (GM) volume and the cortical thickness of the brain, especially in cortico-basal ganglia motor loops, in Parkinson’s disease (PD) with diphasic dyskinesia. 48 PD patients with diphasic dyskinesia, 60 PD patients without dyskinesia and 48 healthy controls (HC) were included. Voxel-based morphometry (VBM) was applied to get GM images from MRI brain images. FreeSurfer was used to get cortical thickness. Distinct analyses of covariance (ANCOVA) and linear contrasts were performed for early- and late-onset PD groups. The severity of diphasic dyskinesia was evaluated by the Unified Dyskinesia Rating Scale (UDysRS). Finally, the correlations between mean volumes of clusters showing differences and the UDysRS scores were performed by Pearson’s correlation. The GM volumes of precentral gyri were increased in PD patients with diphasic dyskinesia when compared with those without dyskinesia, which were positively correlated with UDysRS scores in PD patients with diphasic dyskinesia. However, there was no significant difference in cortical thickness among groups. The increased precentral gyri GM volumes might be associated with the pathogenesis and the severity of diphasic dyskinesia.

Neurophysiology of the brain stem in Parkinson's disease

Parkinson's disease (PD) is predominantly idiopathic in origin, and a large body of evidence indicates that gastrointestinal (GI) dysfunctions are a significant comorbid clinical feature; these dysfunctions include dysphagia, nausea, delayed gastric emptying, and severe constipation, all of which occur commonly before the onset of the well-known motor symptoms of PD. Based on a distinct distribution pattern of Lewy bodies (LB) in the enteric nervous system (ENS) and in the preganglionic neurons of the dorsal motor nucleus of the vagus (DMV), and together with the early onset of GI symptoms, it was suggested that idiopathic PD begins in the ENS and spreads to the central nervous system (CNS), reaching the DMV and the substantia nigra pars compacta (SNpc). These two areas are connected by a recently discovered monosynaptic nigro-vagal pathway, which is dysfunctional in rodent models of PD. An alternative hypothesis downplays the role of LB transport through the vagus nerve and proposes that PD pathology is governed by regional or cell-restricted factors as the leading cause of nigral neuronal degeneration. The purpose of this brief review is to summarize the neuronal electrophysiological findings in the SNpc and DMV in PD.

Parkinson's Disease

The diagnosis of Parkinson disease (PD) is based on the presence of bradykinesia and either resting tremor or rigidity and there should be no features from the history or examination to suggest an alternative cause of parkinsonism. In addition to the motor manifestations of PD, there is a long list of nonmotor symptoms, several of which occur before motor signs and are considered "prodromal" PD. These are classified as neuropsychiatric, autonomic, sleep, and sensory. There are many medical options for the treatment of PD but levodopa remains the mainstay. Deep brain stimulation and other advanced therapies are also available.

Chemical management of levodopa-induced dyskinesia in Parkinson's disease patients

INTRODUCTION

Levodopa-induced dyskinesias (LID) appears in more than 50% of Parkinson's disease patients after 5 years of treatment and clinicians always have to ensure that there is a balance between the beneficial effect of the treatment and the potential complications.

AREAS COVERED

In this review, the authors discuss the treatment of LID. Treatment can be divided into strategies for preventing their occurrence, modification of dopaminergic therapy, and providing more continuous dopaminergic stimulation as well as the use of nondopaminergic drugs.

EXPERT OPINION

Amantadine is currently considered the most effective drug for the treatment of LID. Several compounds developed to target adenosine, adrenergic, glutamatergic, and serotonergic receptors have shown to significantly decrease dyskinesias in animal models. However, despite promising preclinical results, translation to clinical practice remains challenging and majority of these compounds failed to decrease LID in randomized controlled trials with moderate-to-advanced parkinsonian patients. Despite promising results with nondopaminergic drugs, treatment of dyskinesias is still challenging and largely due to their side effects. Future research should focus on developing treatments that can provide continuous dopaminergic delivery throughout the day in a noninvasive manner. Studies on the impact of the early administration of long-acting formulations of levo-3,4-dihydroxy-phenylalanine on dyskinesias are also necessary.

L-DOPA for Parkinson's disease-a bittersweet pill

3,4-dihydroxy-L-phenylalanine (L-DOPA) is the gold standard treatment for Parkinson's disease. It has earned that title through its highly effective treatment of some of the motor symptoms in the early stages of the disease but it is a far from perfect drug. The inevitable long-term treatment that comes with this chronic neurodegenerative condition raises the risk significantly of the development of motor fluctuations including disabling L-DOPA-induced dyskinesia. Being unsurpassed as a therapy means that understanding the mechanisms of dyskinesia priming and induction is vital to the search for therapies to treat these side effects and allow optimal use of L-DOPA. However, L-DOPA use may also have consequences (positive or negative) for the development of other interventions, such as cell transplantation, which are designed to treat or repair the ailing brain. This review looks at the issues around the use of L-DOPA with a focus on its potential impact on advanced reparative interventions.