Eye Movements in Parkinson's Disease and Inherited Parkinsonian Syndromes

Eye movement abnormalities in movement disorders

The visual system represents the most well-developed sensory system in humans, who are highly dependent on vision for organized response to their environment. The region of eye that is responsible for sharp central vision is the fovea. Thus, to see the world, images of objects of interest should fall on fovea. This is achieved through various sets of eye movements, all of which work together to keep the image of the target object on the fovea. It is therefore not surprising that a large part of the human brain is devoted to eye movements (e.g., several cortical and subcortical areas, including the brainstem, cerebellum and basal ganglia). Given that a large area of brain is devoted to eye movements, it is not surprising to find eye movement abnormalities in various brain disorders, including movement disorders. In fact, many of the movement disorders commonly encountered in clinical practice are associated with characteristic eye movement abnormalities that not only help in specific diagnosis, but also contribute to morbidity associated with these disorders. In this article, we review the pathophysiology, clinical characteristics, and significance of various eye movement abnormalities in patients with various movement disorders.

Pro-Saccades Predict Cognitive Decline in Parkinson's Disease: ICICLE-PD

BACKGROUND

Cumulative dementia incidence in Parkinson's disease (PD) is significant, with major personal and socioeconomic impacts on individuals with PD and their carers. Early identification of dementia risk is vital to ensuring optimal intervention. Saccadic deficits often distinguish neurodegenerative disorders and cognitive impairment, but their ability to predict cognitive decline in PD has yet to be determined. The aims of this study were to (1) evaluate baseline (6.4 ± 6.1 months since PD diagnosis) differences in pro-saccadic metrics between those with early PD and healthy age-matched adults; and (2) assess the ability of baseline pro-saccades to predict subsequent cognitive decline over 4.5 years.

METHODS

One hundred and forty-one PD and 90 age-matched participants recruited at diagnosis underwent saccadometric assessment of pro-saccades at baseline and had cognition assessed at baseline, 18, 36, and 54 months. Pro-saccadic characteristics included latency, duration, amplitude, peak, and average velocity. Cognitive assessment included executive function, attention, fluctuating attention, and memory. Linear mixed-effects models examined pro-saccadic metrics as predictors of cognitive decline over 54 months.

RESULTS

Pro-saccades were significantly impaired at baseline in PD compared with controls. Pro-saccadic characteristics of latency, duration, peak, and average velocity predicted decline in global cognition, executive function, attention, and memory over 54 months in PD. In addition, only reduction in global cognition and attention were predicted by pro-saccadic metrics in age-matched adults, indicating that PD findings were not purely age related.

CONCLUSIONS

Saccadic characteristics are impaired in early PD and are predictive of cognitive decline in several domains. Assessment of saccades may provide a useful non-invasive biomarker for long-term PD cognitive decline in early disease. © 2019 International Parkinson and Movement Disorder Society.

Oculomotor effects of medical and surgical treatments of Parkinson's disease

Oculomotor abnormalities are fast becoming a proxy for disease diagnosis and progression. Saccades-ballistic eye movements-are known to be affected by dopaminergic cell loss in the basal ganglia, caused by Parkinson's disease. Pharmaceutical and neurosurgical interventions such as deep brain stimulation and functional neurosurgery have both been noted to have an effect on saccades. Comparing and contrasting these effects may yield insights into Parkinson's disease pathophysiology, and the mechanisms of pharmacological and neurosurgical treatments. Computational models of saccadic control, such as the LATER model, can help to interpret the distribution of saccadic latencies, providing a framework for objectively comparing the effects of pharmaceutical interventions and deep brain stimulation.

Oculomotor Performances Are Associated With Motor and Non-motor Symptoms in Parkinson's Disease

Background: Parkinson's disease (PD) patients exhibit deficits in oculomotor behavior, yet the results are inconsistent across studies. In addition, how these results are associated with clinical symptoms is unclear, especially in China.

Methods: We designed a case-control study in China including 37 PD patients and 39 controls. Clinical manifestations in PD patients were recorded. Oculomotor performance was measured by a video-based eye tracker system.

Results: We found that six oculomotor parameters, including fixation stability, saccadic latency, smooth pursuit gain, saccade frequency, viewing range, and saccade frequency during free-viewing context, were significantly different in PD patients and control group. Combining application of these six parameters could improve diagnostic accuracy to over 90%. Moreover, pursuit gain was significantly associated with PD duration, UPDRS III, in PD patients. Saccade latency was significantly associated with PD duration, Berg balance score, RBD score, and Total LEDD in PD patients.

Conclusions: PD patients commonly exhibit oculomotor deficits in multiple behavioral contexts, which are associated with both motor and non-motor symptoms. Oculomotor test may provide a valuable tool for the clinical assessment of PD.

Clonazepam improves the symptoms of two siblings with novel variants in the SYNJ1 gene

BACKGROUND

Mutations in the SYNJ1 gene have been associated with early-onset of atypical Parkinson's disease or severe neurodegeneration with intractable seizures. Due to the rarity of the disease, there were limitations in the quality of available treatment options for SYNJ1-related diseases.

METHODS

Two affected siblings from a non-consanguineous family were evaluated through a set of clinical and laboratory tests. The genetic screening was performed through exome next generation sequencing. SYNJ1 mutant transcripts were purified and cloned into the vectors for Sanger sequence of single-stranded DNA. Relative level of the SYNJ1 transcript was measured by quantitative PCR.

RESULTS

The clinical features were characterized by a triad of symptomatic progression including diplopia, dystonia, and Parkinsonism. The dystonic symptoms were outstanding in the siblings, which preceded the Parkinsonism symptoms and became the main symptoms. Clonazepam resolved the clinical symptoms, especially the severe trunk dystonia and dystonic postures of limbs. Compound heterozygous variants (c.2579-2A > G; p.A860Gfs*5 and c.3845C > A; p.P1282L) were identified in the SYNJ1 gene co-segregating in this family. The proline residue is highly conserved across species and predicted to be damaging by several in silico tools. The splice site variant caused a skip of exon 20 and a significant reduction of the SYNJ1 transcript expression.

CONCLUSIONS

Our study expanded the clinical and genetic spectrums of the SYNJ1-related diseases. Although our study was a preliminary observation, it indicated that clonazepam could improve the dystonic symptoms caused by mutations in the SYNJ1 gene.

EEG Microstates Change in Response to Increase in Dopaminergic Stimulation in Typical Parkinson's Disease Patients

Objectives: Characterizing pharmacological response in Parkinson's Disease (PD) patients may be a challenge in early stages but gives valuable clues for diagnosis. Neurotropic drugs may modulate Electroencephalography (EEG) microstates (MS). We investigated EEG-MS default-mode network changes in response to dopaminergic stimulation in PD. Methods: Fourteen PD subjects in HY stage III or less were included, and twenty-one healthy controls. All patients were receiving dopaminergic stimulation with levodopa or dopaminergic agonists. Resting EEG activity was recorded before the first daily PD medication dose and 1 h after drug intake resting EEG activity was again recorded. Time and frequency variables for each MS were calculated. Results: Parkinson's disease subjects MS A duration decreases after levodopa intake, MS B appears more often than before levodopa intake. MS E was not present, but MS G was. There were no significant differences between control subjects and patients after medication intake. Conclusion: Clinical response to dopaminergic drugs in PD is characterized by clear changes in MS profile. Significance: This work demonstrates that there are clear EEG MS markers of PD dopaminergic stimulation state. The characterization of the disease and its response to dopaminergic medication may be of help for early therapeutic diagnosis.