Bipolar Spectrum disorders in Parkinson's disease: a systematic evaluation

Objective: Psychiatric disorders are very common in patients affected by Parkinson's disease (PD). However, comorbidity with Bipolar Spectrum disorders is understudied. The aim of this study is to explore the clinical correlates of PD associated with Bipolar Spectrum disorders. Methods: One hundred PD patients were screened for psychiatric comorbidities, cognitive profile, motor, and non-motor symptoms. The sample was divided into three groups: PD-patients with Bipolar Spectrum disorders (bipolar disorder type I, type II, and spontaneous or induced hypomania; N = 32), PD-patients with others psychiatric comorbidities (N = 39), PD-patients without psychiatric comorbidities (N = 29). Clinical features were compared among the groups using analysis of variance and chi-square test. A logistic regression was performed to evaluate the association between Bipolar Spectrum disorders and early onset of PD (≤50 years) controlling for lifetime antipsychotic use. Results: In comparison with PD patients with and without other psychiatric comorbidity, subjects affected by Bipolar Spectrum disorders were younger, showed more frequently an early onset PD, reported more involuntary movements and a higher rate of impulse control disorders and compulsive behaviors. No differences were observed in indexes of exposure to dopamine agonist treatments. The early onset of PD was predicted by Bipolar Spectrum comorbidity, independently from lifetime antipsychotic use. Conclusion: Bipolar Spectrum disorders are common in early onset PD. The presence of bipolar comorbidity could identify a particular subtype of PD, showing higher rates of neurological and psychiatric complications and deserving further investigation.