The study, “Bipolar disorder and risk of Parkinson disease: A nationwide longitudinal study,” was published in the journal Neurology.
An association between major depressive disorder and Parkinson’s disease has been suggested in previous studies. But such an analysis has not been conducted in people with bipolar disorder, which is characterized by unusual shifts in mood, energy, and activity levels.
Data from a hospital registry previously showed that people with manic or depressive episodes — both experienced by those with bipolar disorder — had an increased risk of being diagnosed with Parkinson’s, but the temporal link between these two events had not yet been properly assessed.
To address this lack of knowledge, researchers conducted a longitudinal study using Taiwan’s National Health Insurance Research Database. Clinical records from 56,340 patients with bipolar disorder (mean age 40 years) and 225,360 healthy individuals, collected between 2001 and 2009 and followed until 2011, were evaluated. None of the participants had a history of Parkinson’s or related diseases at the start of the study.
Patients with bipolar disorder developed Parkinson’s significantly more often than those in the control group (0.7% vs, 0.1%). These patients also had a shorter time from enrollment to Parkinson’s disease diagnosis (4.2 vs. 6.5 years), and were younger when Parkinson’s was identified (64.2 vs. 73 years).
Use of antipsychotic agents was found to have no impact on these findings. The prevalence of cerebrovascular diseases, traumatic brain injury, hypertension, dyslipidemia (abnormal levels of lipids), and diabetes did not differ between the two groups.
Further analysis revealed that adult bipolar patients were about 6.78 times more likely to develop Parkinson’s than controls, while bipolar patients older than 65 had a 3.87 times higher risk.
Patients with a high frequency of hospital admission (more than two times per year) for psychiatric episodes were found to have 5.62 times higher risk of Parkinson’s than patients admitted less than once a year. Also, two or more psychiatric admissions for manic/mixed or depressive episodes were associated with a greater likelihood of having Parkinson’s.
“Our population-based longitudinal study found that patients with bipolar disease had an increased risk of developing [Parkinson’s] later in life compared to the controls,” the researchers wrote.
“Additional experiments are required to obtain a deeper understanding of the mechanisms involved” in the development of these two disorders,” they said. In addition, “medical practitioners should be aware that the risk of subsequent [Parkinson’s] should be particularly considered in patients with bipolar disease, especially those with multiple psychiatric admissions for mood episodes.”