Parkinson's disease may significantly raise the risk of bipolar disorder

We've long known that Parkinson's disease (PD) comes with psychiatric comorbidities — depression and anxiety are common companions. But a new study published in the Journal of Psychiatric Research adds a notable finding: PD patients face a nearly fourfold higher risk of developing bipolar disorder (BD) compared to those without PD. While earlier research flagged BD as a risk factor for subsequent PD, this study suggests the relationship runs both ways.

Researchers analyzed data from over 30,000 individuals in South Korea's national health database (2012–2023), comparing 5,158 PD patients against 25,790 matched controls. The elevated BD risk was consistent across age groups and sexes, and was most pronounced in the first 3 years after a PD diagnosis — though it persisted well beyond that window. Shared biological pathways, including dopaminergic dysfunction and neuroinflammation, may help explain the link.

By the Numbers:

• ~4x higher rate of BD diagnosis in PD patients (IRR: 3.74)
• 13.01 per 1,000 person-years BD incidence in PD vs. 3.48 in controls
• Risk highest within first 3 years post-PD diagnosis (aHR: 3.55)
• 236 PD patients were subsequently diagnosed with BD

Why it matters: BD may be underdiagnosed in PD patients due to overlapping symptoms. Clinicians should consider routine psychiatric screening early after a PD diagnosis — catching BD sooner could meaningfully improve patient outcomes and quality of life.