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Study further suggests link between bipolar disorder, risk for Parkinson’s disease

Joaquim J. Ferreira

Patients with bipolar disorder appeared significantly more likely to develop Parkinson’s disease than the general population, according to results of a systematic review and meta-analysis published in JAMA Neurology.

"The main message for clinical practice is the alert that patients with bipolar disorder may later develop Parkinson's disease and in those patients, Parkinson's disease should be formally diagnosed and properly treated," Joaquim J. Ferreira, MD, PhD, of the Laboratory of Clinical Pharmacology and Therapeutics at the University of Lisbon in Portugal, told Healio Psychiatry. "Patients with bipolar disorder who begin developing, throughout the course of their disease, symptoms similar to those of Parkinson's disease may actually have both diseases and physicians should suspect that those features of parkinsonism may not be just a side effect of the medication used in the treatment of bipolar disorder."

The researchers noted that physicians may misdiagnose Parkinson’s disease as drug-induced parkinsonism. They conducted the current study to evaluate the possible association of bipolar disorder with a later diagnosis of idiopathic Parkinson’s disease.   

Faustino and colleagues extracted data from seven prospective, retrospective and cross-sectional studies that included a total of 4,374,211 participants. Results of the meta-analysis showed that, compared with individuals without bipolar disorder, those previously diagnosed with bipolar disorder had an increased likelihood of a subsequent diagnosis of idiopathic Parkinson’s disease (OR = 3.35; 95% CI, 2-5.6; I² = 92%). A sensitivity analysis, for which researchers removed studies that had a high risk for bias, also showed an increased risk for Parkinson’s disease among individuals with bipolar disorder (OR = 3.21; 95% CI, 1.89-5.45; I² = 94%). Researchers noted that preplanned subgroup analyses according to diagnostic certainty and study design did not show a significant effect.

“In addition to the important implications for clinical practice of psychiatrists and neurologists, these findings will open the door to investigate the biological link between these two clinical entities and also reopen the discussion on the possible long-term side-effects of antipsychotic drugs. – by Joe Gramigna

Disclosures: Ferreira reports grants and personal fees from Allergan, GSK, Novartis and Teva Pharmaceuticals, among other industry ties. Please see the study for all other authors’ relevant financial disclosures.