Treatment of parkinsonism with levodopa. Follow-up after 2 years of treatment

Tremor in Parkinson's Disease: From Pathophysiology to Advanced Therapies

Background

Tremor is one of the most prevalent symptoms in Parkinson's Disease (PD). The progression and management of tremor in PD can be challenging, as response to dopaminergic agents might be relatively poor, particularly in patients with tremor-dominant PD compared to the akinetic/rigid subtype. In this review, we aim to highlight recent advances in the underlying pathogenesis and treatment modalities for tremor in PD.

Methods

A structured literature search through Embase was conducted using the terms "Parkinson's Disease" AND "tremor" OR "etiology" OR "management" OR "drug resistance" OR "therapy" OR "rehabilitation" OR "surgery." After initial screening, eligible articles were selected with a focus on published literature in the last 10 years.

Discussion

The underlying pathophysiology of tremor in PD remains complex and incompletely understood. Neurodegeneration of dopaminergic neurons in the retrorubral area, in addition to high-power neural oscillations in the cerebello-thalamo-cortical circuit and the basal ganglia, play a major role. Levodopa is the first-line therapeutic option for all motor symptoms, including tremor. The addition of dopamine agonists or anticholinergics can lead to further tremor reduction. Botulinum toxin injection is an effective alternative for patients with pharmacological-resistant tremor who are not seeking advanced therapies. Deep brain stimulation is the most well-established advanced therapy owing to its long-term efficacy, reversibility, and effectiveness in other motor symptoms and fluctuations. Magnetic resonance-guided focused ultrasound is a promising modality, which has the advantage of being incisionless. Cortical and peripheral electrical stimulation are non-invasive innovatory techniques that have demonstrated good efficacy in suppressing intractable tremor.

Frequency of levodopa-related dyskinesias and motor fluctuations as estimated from the cumulative literature

There is no clear consensus regarding the frequency (and hence, the risk), of dyskinesias or motor fluctuations during chronic levodopa therapy for Parkinson's disease (PD). Multiple clinical series have tabulated these frequencies since the advent of levodopa over 30 years ago. We were interested in determining: (1) the aggregate frequency figures in the existing literature; and (2) how clinical series from the early levodopa era, which included patients with longer durations of parkinsonism, compare to more recent (modern era) series. We searched MEDLINE for all English language publications reporting the cumulative frequency of levodopa-induced dyskinesias or motor fluctuations during discrete intervals of treatment. This generated 2,478 publications spanning 1966 through September 2000. Papers with appropriate titles or abstracts were reviewed; reference lists from published clinical series were a source of additional papers for review. This ultimately yielded 74 publications with adequate data, relating to 112 intervals of levodopa treatment. Series that included patients with PD-onset well before levodopa availability (pre-levodopa era) were separately analyzed from all subsequent series. Series were grouped by duration of levodopa therapy and the median frequencies of dyskinesias and motor fluctuations were tabulated for each group. The data were analyzed both with and without adjustment for the number (N) in each series. Among series containing pre-levodopa era patients, the median dyskinesia frequency was already 50% by 5-6 months of treatment. This contrasts with the modern era series where dyskinesias were reported later in treatment. The median dyskinesia frequency was slightly less than 40% by 4-6 years of levodopa therapy among modern era patients. Motor fluctuations (wearing-off) were not tabulated in most of the early levodopa series. Among modern era reports, motor fluctuations were nil during the first year of levodopa therapy but were experienced by approximately 40% of patients by 4-6 years of treatment. Similar results were found when the analyses were restricted to only prospective studies where levodopa motor complications were targeted outcome measures. The conclusions reached were: (1) patients from the pre-levodopa era experienced dyskinesias much earlier during levodopa treatment than modern era patients, perhaps because of longer durations of pre-existing PD; (2) in the present era, patients treated with levodopa therapy for 4-6 years have approximately a 40% likelihood of experiencing motor fluctuations and a risk of dyskinesias just short of 40%; and (3) these findings represent incident data and the prevalence of clinically important morbidity may be substantially less.

The Sydney Multicentre Study of Parkinson's disease: a report on the first 3 years

One hundred and twenty nine de novo patients with idiopathic Parkinson's disease are being followed over a 5 year period in a double-blind multicentre study comparing low-dose bromocriptine (less than 30 mg/day) with low-dose levodopa-carbidopa (less than 600/150 mg/day). Sixty six patients have been randomised to bromocriptine and 63 patients to levodopa-carbidopa. Improvement has been greater in the levodopa-carbidopa group than in the bromocriptine group. Involuntary movements have so far only occurred in patients on levodopa-carbidopa, the incidence being much lower than is usually described with conventional doses. Mild, end-of-dose failure has occurred in both treatment groups; however, no patient has developed the "on-off" phenomenon. Low-dose levodopa-carbidopa appears to be a more effective anti-Parkinsonian treatment than low-dose bromocriptine but more prone to cause dyskinesia.

Cerebral atrophy and long-term response to levodopa in Parkinson's disease

In 92 parkinsonian patients (42 men, 50 women) aged from 37-79 years (mean 62.8) the impact of cerebral atrophy as assessed by computed tomography on the course of the clinical symptomatology under levodopa during a period of 1 to 5 years was investigated. It could be shown that patients suffering from medium to severe degrees of atrophy-independent of its special location--have a less favorable response than those with normal CT findings. The data do not allow a definite decision whether cortical artrophy or ventricular enlargement are of major importance. At any rate, the width of the third ventricle seems to have no influence on the course of the clinical symptoms. After 3 years of levodopa treatment a dissociation between cerebral atrophy and therapeutic effectiveness can be observed.