..Seven studies were eligible for inclusion and included 4 374 211 participants overall. A previous diagnosis of BD increased the likelihood of a subsequent diagnosis of idiopathic PD (odds ratio, 3.35; 95% CI, 2.00-5.60; I2 = 92%). A sensitivity analysis was performed by removing the studies that had a high risk of bias and also showed an increased risk of PD in people with BD (odds ratio, 3.21; 95% CI, 1.89-5.45; I2 = 94%). Preplanned subgroup analyses according to study design and diagnostic certainty failed to show a significant effect.
Conclusions and Relevance This review suggests that patients with BD have a significantly increased risk of developing PD compared with the general population. Subgroup analyses suggested a possible overestimation in the magnitude of the associations. These findings highlight the probability that BD may be associated with a later development of PD and the importance of the differential diagnosis of parkinsonism features in people with BD.