In a retrospective case-matched study from Taiwan published in Neurology, persons with bipolar disorder (BPD) were almost 7 times more likely to develop Parkinson’s disease (PD). Incidence of PD in people with BPD was 0.7% vs 0.1% for those without BPD (HR 6.95; 95% CI: 6.95-8.02). Onset of PD earlier in those with BPD (64 vs 73 years; P < .001). For those with BPD, the risk of PD increased with the number of hospitalizations for psychiatric symptoms.
These findings suggest a diagnosis of BPD with other findings of PD risk factors (eg, positive dopamine transporter [DaT] scan or REM sleep behavior disorder [RBD]) could identify individuals with prodromal PD. If preventive or disease-modifying treatments are developed, this could help identify individuals for early treatment. The findings also reaffirm that treatments for BPD and PD may act on similar disease mechanisms, which has implications for treatment planning. For example, it is important to be aware that deep brain stimulation (DBS) for PD may cause mania and that mood stabilizers can worsen parkinsonism.
“Previous studies have shown a relationship between depression and Parkinson’s disease, but few studies have looked at whether there is a relationship between BPD and PD,” said author Mu-Hong Chen, MD, PhD, of Taipei Veterans General Hospital in Taiwan, noting that “Further studies are needed to investigate whether these diseases share underlying processes or changes in the brain. . . that could include genetic alterations, inflammatory processes, or problems with the transmission of messages between brain cells. If we could identify the underlying cause of this relationship, that could potentially help us develop treatments that could benefit both conditions.”
In the study, 56,340 individuals diagnosed with BPD between 2001 and 2009 with no history of PD, were identified and matched to 4 other individuals of the age, sex, time of diagnosis/enrollment, comorbid conditions, income, and level of urbanization. All 281,700 individuals were followed through 2011. Sensitivity analysis was used to control for time of enrollment and exposure to antipsychotic drugs. Limitations include the small geographic area that could allow confounding genetic factors and the short time-frame (BPD and PD may both develop well before diagnosis such that BPD could be an early symptom of PD). Despite controlling for antipsychotic drug use, it is still possible that some individuals had drug-induced PD symptoms.