Dopamine transporter availability predicts ICDs

Reduced striatal dopamine transporter availability is already present in patients with Parkinson’s disease (PD) who go on to develop impulse control disorders (ICDs), a study shows.

The finding supports those of previous studies, but the researchers say that “in contrast to our design, these studies were performed in patients that had already developed ICD, and so the reduced dopamine transporter availability also could also have been the consequence of prolonged dopamine replacement therapy or brain alterations associated with ICD.”

Chris Vriend (VU University Medical Center, Amsterdam, the Netherlands) and co-workers studied 31 PD patients who had no symptoms of ICD when they underwent single-photon emission computed tomography, prior to starting dopamine replacement therapy.

During an average follow-up period of 31.5 months, 11 patients developed ICD symptoms, as assessed using the Scales for Outcomes in Parkinson’s disease–Psychiatric Complications. These patients had significantly lower baseline dopamine transporter binding ratios in the right ventral striatum, right anterior-dorsal striatum and right posterior putamen, relative to patients who did not develop ICDs.

The two groups were of similar age and did not differ with regards to disease stage or duration or Mini-Mental State Examination score. However, the ICD patients had a longer interval between baseline and follow-up (38.4 vs 27.9 months), were more often men, and had higher Beck’s Depression Inventory scores and a higher levodopa equivalent daily dose.

Nevertheless, the between-group differences in dopamine transporter binding ratios persisted after post-hoc analyses to control for these variables.

Furthermore, higher scores on the Questionnaire for Impulsive-Compulsive disorders in Parkinson’s disease–Rating Scale (specifically the sum of the subscores on gambling, sexual, buying and eating behaviours) were associated with lower age-normalised binding ratios in the right ventral striatum and right anterior-dorsal striatum. These associations also persisted after post-hoc adjustments.

The researchers note in Movement Disorders that their “main finding of reduced ventral striatal dopamine transporter availability in de novo PD patients susceptible to ICD may have two non-mutually exclusive interpretations”. These are a premorbid reduced availability of dopamine transporter or more pronounced dopaminergic denervation in the course of PD, they say.

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