People with Bipolar Disorder Have a Greater Risk of Developing Parkinson’s Disease

There exists a link between bipolar disorder (BD) and Parkinson’s disease (PD), according to a new study. Patients with BD have a significantly higher chance of developing PD than others in the general population. The findings appeared in JAMA Neurology.

The research authors wrote in their introduction that: “The standard treatment for BD that includes lithium, antipsychotic medications, and antiepileptic medications may be associated with drug-induced parkinsonism, which is not clinically distinguishable from PD, both being characterized by bradykinesia, resting tremor, rigidity, and postural instability. Since drug-induced parkinsonism is more common among patients with BD, physicians may be more inclined to misdiagnose PD as drug-induced parkinsonism.”

To conduct this study, researchers performed a literature search of the following online databases from inception until May 2019: Cochrane Controlled Register of Trials; MEDLINE, Embase; and PsycINFO, using the terms Parkinson’s disease, bipolar disorder, and mania. Although they assessed studies of any design, they were particularly focused on examining cohort, case-control, or cross-sectional studies that reported data on the link between idiopathic PD in BD versus non-BD populations. Subsequently, they pulled any articles identified as relevant by at least one review author, while two review authors independently screened each full text article, and convened discussions to resolve any discrepancies. They pooled data utilizing a random-effects model and reported results using odds ratio (OR) estimates with corresponding 95% CIs, while reporting heterogeneity as I2. In total, seven studies were deemed eligible for inclusion, and those studies comprised 4,374,211 participants.

Findings and Clinical Implications

According to the study results, patients with a previous diagnosis of BD had a notably increased chance of a subsequent diagnosis of idiopathic PD (OR=3.35; 95% CI, 2.00 to 5.60; I2 = 92%). Moreover, a sensitivity analysis that was conducted by removing the studies that had a high risk of bias also revealed an increased risk of PD in people with BD (OR=3.21; 95% CI, 1.89 to 5.45; I2 = 94%). “The findings of this systematic review and meta-analysis suggest that people with BD have a significantly increased likelihood of later developing PD. When placed in the context of other systematic reviews looking at risk factors for PD, our statistical evidence is highly suggestive,” the authors wrote.

They added that: “The main clinical implication of this review should be to underline that if patients with BD present with parkinsonism features, this may not be drug induced and may recommend the investigation of PD. To clinically distinguish parkinsonism from PD in clinical practice, the use of functional neuroimaging methods may be of particular interest, as PD classically presents with nigrostriatal degeneration while drug-induced parkinsonism does not.”