Starting treatment earlier does not appear to worsen the course of Parkinson’s disease or be associated with more severe treatment side effects, an observational study reports.
The study, “Estimating the Effect of Early Treatment Initiation in Parkinson’s Disease Using Observational Data,” was published in the journal Movement Disorders.
People with Parkinson’s and their clinicians may decide to delay beginning treatment for a variety of reasons, including concerns about side effects or that the treatment might accelerate the underlying disease. Clinical trials testing dopamine replacement therapies, such as levodopa and others, have so far found no evidence that such treatments speed the course of the disease, though clinical findings pertaining to its long-term benefits have been mixed.
Clinical trials are essential to assess the safety and effectiveness of treatments in a controlled and unbiased manner. However, clinical trials also have limitations. For example, these studies typically have fairly short follow-up times, and treatments dispensed in the context of a clinical trial are not always identical to those used in day-to-day clinical practice.
Observational data — information obtained simply by observing differences among people in a real world setting — also present challenges, especially the fact that such findings are less resilient to potential confounders (variables), compared with clinical trial data.
“When such challenges in analyzing observational data are addressed carefully, these types of data can be valuable sources of complimentary evidence regarding the outcomes of real‐world clinical decisions,” the authors wrote.
“Our goal here is to estimate the long‐term effect of early or delayed start of treatment in patients with [recently diagnosed Parkinson’s] using longitudinal, observational data,” they wrote.
Investigators analyzed data from approximately 300 people who were part of the de novo cohort of the Parkinson’s Progression Markers Initiative, an ongoing observational study that uses different techniques to identify new biomarkers of disease progression. Patients included in the de novo cohort had been diagnosed with Parkinson’s recently (two years or less) and were not expected to require immediate treatment, although they remained in the study if that was the case.
Most patients in the group were men (67%), with an average age of 61.3 years. The most common treatment used was levodopa (45%).
Taking advantage of the fact that there was natural variation as to when these individuals began treatment, researchers assessed whether people who started treatment earlier had different outcomes compared with those who started treatment later. Statistical adjustments were made to account for possible confounders, for example, how an individual who already has a more severe disease might be more likely to start treatment earlier.
“We used a rigorous approach using models that considered the time‐varying nature of treatment initiation, thereby effectively removing some confounding that is present in simpler models,” the researchers wrote.
The main goal, or outcome, measured was motor function in “off” periods — times when symptoms cease to be controlled by medication — as assessed by the MDS‐UPDRS Part III. Outcomes were compared between the two groups of patients after two, three, and four years; not all individuals had data available for every time point.
Overall, people who started treatment earlier tended to have lower scores — indicating less-severe symptoms — at later time points. However, most of these score differences between the two groups were not sufficient to reach statistical significance.
When individuals treated only with levodopa were included in the analysis, earlier treatment was associated with lower scores after two years, and this difference was statistically significant. At later time points, the same trend was evident, but the difference again was not statistically significant.
Other outcome measures, which included non-motor symptom assessments, generally did not find significant differences between people who started treatment earlier or later.
“These data do not provide evidence that earlier treatment initiation leads to consistently worse motor symptoms, non-motor symptoms, and functional disability,” the researchers wrote.
Side effects from treatment also were generally not found to be more common in people who started treatment earlier. The only exception was a small, but significant, increase in dyskinesias (involuntary movements) after three years.
“These findings should further alleviate concerns that early initiation of dopaminergic therapy leads to more severe side effects,” they wrote.
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