Almost half of people in the early stages of Parkinson’s disease already have signs of neurodegeneration in a brain region called the caudate, which was previously thought to affect mostly those at advanced disease stages, a study reports.
Early caudate involvement on both sides of the brain, as seen by DaTscan imaging of the brain, appeared to predict the risk for worse outcomes, including cognitive impairment, depression, and gait problems, over a four-year follow-up period.
These findings suggest that caudate involvement detected through DaTscan neuroimaging may serve as an early biomarker to identify patients at a greater risk of faster disease progression in the near future.
The study, “Clinical implications of early caudate dysfunction in Parkinson’s disease,” was published in the Journal of Neurology, Neurosurgery & Psychiatry.
Parkinson’s disease is believed to be caused by the impairment or death of dopamine-producing nerve cells (neurons) in a region of the brain called the substantia nigra, which controls the body’s balance and movement.
When the disease is established, or advanced, the degeneration of dopaminergic neurons and nerve fibers frequently extends to a brain region called the caudate nucleus. This region plays important roles in motor control as well as in various other non-motor tasks, such as learning and sleep.
In fact, the loss of dopaminergic function in this region is known to contribute to the hallmark symptoms of Parkinson’s including cognitive impairment, depression, sleep disorders, and gait problems.
Although less common, caudate dopaminergic dysfunction may also emerge in the early stages of the disease, in which case it could also contribute to the onset of non-motor symptoms. However, the frequency of this specific brain impairment in early Parkinson’s is unknown as are its clinical implications for patients.
To address this lack of knowledge, a team, led by researchers at the University of Milan in Italy and Newcastle University in England, investigated the prevalence of caudate dopaminergic dysfunction in people who were still in the very early stages of Parkinson’s.
By comparing the participants’ state at the beginning of the study and four years later, they also looked for associations between caudate involvement and an increased risk of disease progression.
They analyzed clinical data from 397 patients who had had a Parkinson’s diagnosis for two years or less, and were participating in the Parkinson’s Progression Markers Initiative (PPMI), an ongoing study attempting to identify biomarkers of disease progression. The team compared the collected clinical data from Parkinson’s patients with that of 177 healthy volunteers.
Caudate dysfunction was detected using 123I-FP-CIT single-photon emission computed tomography, commonly known as DaTscan. This is an imaging technique that depicts the levels of dopamine transporters in the brain that is often used to confirm a Parkinson’s diagnosis.
Based on DaTscan imaging data, the participants were divided into three groups: those who had no reduction of dopamine transporters, those who showed reduction in just one side of the brain, and those who had involvement of both sides of the brain.
Initial data showed that 51.6% of the patients had signs of normal caudate dopamine function, while 26% had caudate dopaminergic dysfunction on one side of the brain (unilateral), and 22.4% on both sides (bilateral).
In general, after four years of follow-up, more patients showed a loss of dopaminergic nerve fibers in the caudate, compared with the study start, affecting 83.9% of patients (unilateral 22.5%, bilateral 61.4%).
“In this study, we have demonstrated a high frequency of early caudate dopaminergic dysfunction in patients with recently diagnosed [Parkinson’s disease],” the researchers wrote.
“Our study suggests that early bilateral caudate dopaminergic dysfunction is associated with an increased frequency of clinically significant depression and to worse depressive symptoms, regardless of age,” they added.
DaTscan parameters used to define the presence of early caudate dysfunction may be a “valid indicator of more rapid onset of such symptoms,” they said, which may help in “identifying patients at risk of clinical progression to cognitive impairment, depression, and gait problems in the near future.”
Assessment of caudate dopaminergic denervation may also assist clinicians in better predicting disease course at an early stage and identifying patients who may benefit the most from early, targeted disease-modifying therapies.