A recent meta-analysis investigated the relationship between bipolar disorder and Parkinson’s disease, examining whether such association may be inherent or due to drug-induced effects.
Bipolar disorder is one of the most severe and complex psychiatric disorders. It is characterized primarily by the shifting of mood states from one extreme (i.e., depressive state) to another (i.e., manic).
Bipolar disorder is believed to have a robust biopsychological basis, and treatment often includes a combination of several medications – lithium, antipsychotics, and/or antiepileptic medications.
Such a combination of medications has been associated with a condition called drug-induced parkinsonism. Being clinically indistinguishable from Parkinson’s disease, drug-induced parkinsonism is often diagnosed in patients with bipolar disorders.
This phenomenon led professionals to question whether bipolar disorder and Parkinson’s disease are associated over and above the effects of medication. In other words, what if doctors’ tendency to diagnose bipolar patients with drug-induced parkinsonism is, in fact, a mistake?
To test this, a group of researchers from Portugal, Italy, and the United Kingdom, set out to examine in a systematic manner the data from seven different studies on bipolar disorder and Parkinson’s disease. The researchers were interested in determining whether an association exists between patients with Parkinson’s disease and bipolar disorder, over and above any drug-induced symptoms. Being a meta-analysis and systematic review, the researchers’ data pool included over 4.3 million participants from the selected studies.
As published in JAMA Neurology, the researchers found that a previous diagnosis of bipolar disorder significantly increased the likelihood of a subsequent Parkinson’s disease diagnosis. In addition, the researchers discovered that when the study followed up with the patients within a shorter period of time (nine years or less), they were more likely to be diagnosed with Parkinson’s disease.
The researchers suggest that the relationship between the two disorders may be due to the dysregulation of the neurotransmitter dopamine. In bipolar disorder, patients cycle between higher and lower receptor sensitivity, which is believed to be associated with the two extremes in mood. Over time, such cycles of dopamine dysregulation may create an overall reduction in the neurotransmitter, which is also correlated with Parkinson’s disease.
In terms of the increased diagnosis in the shorter follow-up studies, the researchers suggest that this may be indicative of a trend of misdiagnosis. Such evidence should be further investigated, but the researchers continue to suggest that efforts should be concentrated on bettering the diagnostic procedures. Neuroimaging is one such procedure that may help differentiate between drug-induced parkinsonism and Parkinson’s disease.
Written by Maor Bernshtein
Reference: Faustino, P. R., Duarte, G. S., Chendo, I., Caldas, A. C., Reimão, S., Fernandes, R. M., … Ferreira, J. J. (2019). Risk of Developing Parkinson Disease in Bipolar Disorder. JAMA Neurology. doi: 10.1001/jamaneurol.2019.3446
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