We read with great interest a recent review by Savica et al1 on how research on nonmotor symptoms of Parkinson disease (PD) may help understand when PD starts. Research on PD nonmotor symptoms may eventually lead to earlier disease diagnosis, improved clinical management, and better understanding of PD natural history and pathoetiology.
Prospective epidemiological studies are particularly important for this kind of research, as they evaluate nonmotor symptoms of PD before its clinical diagnosis; However, such studies were not available until recently. In addition to the data that were summarized in the review,1 large prospective cohort studies showed that other symptoms might also precede PD clinical onset or diagnosis. These symptoms include unexplained weight loss,2 sense of imbalance,3 erectile dysfunction,4 and longer daytime napping.5 For example, using biennially reported body weights from the participants in 2 large cohorts, we found that patients with PD began to lose weight 2 to 4 years before diagnosis2; intriguingly, during the mean time, they tended to increase food intake and decrease physical activity.6 While none of these symptoms are specific to PD, when combined, they may eventually improve our ability to identify individuals at high risk of PD or at an early stage of PD.
Chen H, Gao X, Ascherio A. Prospective Research on Parkinson Nonmotor Symptoms. Arch Neurol. 2011;68(1):135-138. doi:10.1001/archneurol.2010.332