Parkinson disease and impulse control disorders: a review of clinical features, pathophysiology and management.

Impulse control disorders (ICDs) are a heterogeneous group of conditions involving repetitive, excessive and compulsive activities that interfere with life functioning. Examples are pathological gambling, compulsive shopping and hypersexuality. Over the last decade, ICDs have become increasingly recognised as being associated with Parkinson disease (PD), with the literature highlighting a link between dopamine replacement therapy and the development of ICDs. Patients who develop ICDs in the context of compulsive anti-Parkinsonian drug use are described as having dopamine dysregulation syndrome (DDS), which is associated with repetitive complex stereotyped behaviours called punding. Case-control and observational studies have further noted that patients with PD who develop ICDs are more likely to have younger-onset PD, a history of alcohol dependence, novelty-seeking personality traits and psychiatric comorbidities. The pathophysiology of underlying mechanisms is not fully understood, but recent evidence suggests that dopaminergic drugs, particularly dopamine agonists, coupled with changes in reward pathways involving the ventral striatal and related circuitry, may play a role. Neuroimaging studies using positron emission tomography and functional MRI have provided valuable information in this area: patients with DDS have been found to show enhanced dopamine release in the ventral striatum, suggesting functional abnormalities in the mesolimbic networks. Management of ICDs in patients with PD can be challenging, as they may not be aware of a change in their behaviour or may conceal their symptoms to avoid embarrassment. Currently, there is no clear evidence of an optimal treatment. Management is based on a careful balance of dopaminergic drugs with control of the aberrant behaviour, supported by psychological interventions. This review aims to summarise the current literature on ICDs, their phenomenology, epidemiology, clinical features, pathophysiology and management.