The impact of Parkinson's disease on quality of life may vary depending on age at onset. We investigated the effect of age at onset on quality of life in a large Parkinson's disease population (n = 426) using a disease-specific rating scale (PDQ-39) and with careful adjustment for confounding and intermediary factors. We also explored the relationship between depression and excessive daytime sleepiness by age at onset and compared this with the general population. We found that a younger age at onset was significantly associated with worse overall quality of life scores (odds ratio, 2.66; 95% confidence interval, 1.39-5.09; P = .003), but this was attenuated by adjustment for depression as an intermediary factor (odds ratio, 1.86; 95% confidence interval, 0.84-4.11; P = .13). Younger onset was also a risk factor for poor emotional well-being independent of depression status. Risk of depression and excessive daytime sleepiness were elevated in patients with Parkinson's disease compared with controls (odds ratio, 2.99; 95% confidence interval, 1.93-4.65; P < .001; and odds ratio, 3.84; 95% confidence interval, 2.56-5.75; P < .001, respectively), with similar findings seen in both early- and late-onset groups. Our study highlights the need for accurate diagnosis and treatment of depression in younger-onset patients in order to improve quality of life.
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