Bipolar Disorder as a Long-Term Risk Factor for Parkinson's Disease: A Nationwide Case-Control Study

Area of Science:

• Neuroscience
• Psychiatry
• Epidemiology

Background:

• Previous research indicates a connection between bipolar disorder (BD) and Parkinson's disease (PD).
• The long-term temporal relationship and influence of diagnostic duration between BD and PD risk remain unclear.

Purpose of the Study:

• To investigate the association between BD and PD over extended time windows.
• To examine PD risk across various exposure durations preceding PD diagnosis, up to 35 years.

Main Methods:

• A nationwide, register-based, nested case-control study in Finland.
• Included 22,189 PD patients and 148,009 matched controls, analyzing BD diagnoses from 1972 onwards.
• Conditional logistic regression assessed BD-PD association with lags up to 35 years, focusing on an 8-year lag.

Main Results:

• BD diagnoses preceded PD diagnosis in 0.87% of PD patients versus 0.34% of controls.
• An elevated PD risk was observed with a 20-year lag, showing a trend even at 30 years.
• BD diagnosis was associated with a more than twofold increased relative risk of PD (aOR 2.32, 95% CI 1.85-2.91) with an 8-year lag.

Conclusions:

• Bipolar disorder is significantly associated with an elevated risk of Parkinson's disease, detectable decades prior to PD onset.
• Findings suggest BD may represent a long-term vulnerability to PD, not just a prodromal state.
• Further research into shared pathophysiological mechanisms underlying BD and PD is warranted.