Impulsivity Is Associated With Decision-Making Deficits in De-Novo Parkinson's Disease

To the Editor: In a recent study,¹ 30 de-novo Parkinson's disease (PD) patients were assessed with the Iowa Gambling Task (IGT),² reporting preserved decision-making, as compared with healthy controls. In healthy subjects, an elevated impulsivity is associated with poor decision-making, probably due to a poor integration of feedback into the choice among different options.³ In PD patients, the early detection of impulsive features is necessary to prevent the possible development of impulse-control disorders (ICD) once dopaminergic therapy begins.⁴ If, in the sample of de-novo PD patients, IGT performances were not related to impulsivity,¹ are extreme levels of impulsivity (low versus high) associated with different IGT performances, as in healthy subjects?

In the sample of 30 de-novo PD patients, impulsivity was assessed with the Barratt Impulsiveness Scale (BIS-11).⁵ In the whole sample, the mean BIS-11 score was 66.3 (SD: 9.9): the criterion of a score >1 SD from the mean identified five low-impulsive (BIS-11 scores: 49, 53, 54, 55, 56) and five high-impulsive patients (BIS-11 scores: 79, 79, 79, 84, 85); these patients were found to be low-impulsive or high-impulsive with regard to normative data from healthy subjects.⁵ High-impulsive patients were found to be older (69.8 [3.4] versus 62 [6.2]: p<0.05); no other differences were found for demographic, clinical (UPDRS II and III motor scores), and cognitive (MMSE; Frontal Assessment Battery) characteristics.

Low-impulsive patients reported a significantly higher IGT Total score (20.4 [21.1]) than high-impulsive patients (0.8 [7.3]; U=3.5; p<0.05; W=18.5; p<0.05); examining IGT performances in five blocks of 20 choices, low-impulsive patients reported significantly better performances than high-impulsive patients in the fourth block (U=3.5; p<0.05; W=18.5; p<0.05) and in the fifth block (U=3; p<0.05; W=18; p<0.05). In the global sample, no relationships were found in the univariate analysis between the IGT scores and age, so it could be assumed that different IGT performances of the two subgroups (low-impulsive versus high-impulsive) were not due to different mean ages. Considering that these subgroups did not differ in cognitive status (MMSE and FAB), it could also be assumed that different IGT performances of the two subgroups were not due to cognitive functioning. Therefore, it could be assumed that difference IGT performances of the two subgroups were due to the different levels of impulsivity. Low-impulsive patients outperformed high-impulsive patients, suggesting that high-impulsive patients were less able to alter choice-behavior in response to fluctuations of reward contingencies. In conclusion, a subgroup of de-novo PD patients presents high impulsivity in that this characteristic is associated to mild behavioral decision-making deficits, as in healthy subjects. These patients present an increased risk of subsequently developing an ICD when treated with dopaminergic drugs, suggesting the usefulness of an early neuropsychiatric and neuropsychological assessment in this clinical population. These findings need further confirmation with larger samples of patients.