Parkinson’s disease as a neuropsychiatric disease
Parkinson’s disease is a neurodegenerative disease caused by a loss of dopaminergic neurons in the substantia nigra. The lack of dopamine causes the cardinal symptoms of Parkinson’s disease (PD), which are bradykinesia, rigidity, tremor and postural instability. However, in the past decades, clinicians and researchers have begun to understand that neuropsychiatric symptoms such as depressive symptoms, anxiety, apathy and behavioural problems are very frequent in PD. If untreated, those neuropsychiatric symptoms have a negative impact on the quality of life of patients and their caregivers.
The lack of dopamine leads to depressive symptoms, anxiety and apathy in many patients with PD. In fact, those symptoms often appear years before the onset of the motor symptoms, when the loss of dopaminergic neurons in the brain starts occurring. Once treated with dopaminergic medication, those symptoms are often alleviated. The dopaminergic medication itself can also change behaviour, by increasing motivation and pleasure-seeking activities. This change in behaviour is usually perceived as positive and remains unproblematic in most patients. However, in some patients, increasing dopaminergic medication above a certain individual threshold can induce impulse-control disorders such as pathological gambling, hypersexuality, compulsive shopping, binge eating, excessive hobbyism, punding or an abuse of dopaminergic medication. The treatment of apathy and impulse control disorders remains challenging, as they often develop gradually over time and there are is only little consensus on treatment strategies. We therefore direct our research at better understanding the underlying mechanisms and treatment options for behavioural disorders in PD.
One special area of our research concerns behavioural changes before and after deep brain stimulation (DBS). DBS reduces motor symptoms in advanced Parkinson’s disease via electric stimulation of specific brain areas. Whilst the beneficial effect of DBS on motor symptoms has been proven in many studies, the effect on DBS on neuropsychiatric symptoms remains less clear. Some studies show that impulse control disorders decrease along with tapering of the dopaminergic medication after the DBS surgery. At the same time, studies report that patients gradually develop apathy if medication is reduced markedly after DBS. Yet other studies suggest that there might be new-onset impulse control disorders or hypomania linked to DBS stimulation itself. Our research group is therefore undertaking different research projects that specifically concern behavioural changes before and after DBS.