Aims Cognitive impairment in Parkinson's disease (PD) has been associated with both pathological gambling and apathy. The aim of this study is to investigate, by means of a direct comparison, the neuropsychological associations of three behavioural groups of PD sufferers: impulse control disorder (ICD), apathy and controls.

Methods Non-demented (n=96) PD sufferers were compared on clinical (motor and psychiatric) and cognitive variables. The PD sufferers were divided into three behavioural groups: impulse control disorder (ICD) (n=33); apathy (n=26); and controls (n=37). Correlations between variables were sought.

Results The three behavioural groups differed significantly in set shifting (errors on the Trail Making task part B; p<.001), verbal fluency (FAS task; p=0.006), global cognition (total MMSE; p=0.001) and complex concentration (serial 7’s; p=0.022), with the apathy group being significantly more impaired compared to the other two groups. Correlations were found between measures of complications of therapy and global cognition (UPDRS IV; ñ=0.238; p=0.042); and level of apathy with verbal fluency (Starkstein; ñ=–0.394; p=0.001).

Conclusions Cognitive functioning differs according to behavioural phenotype, with apathy PD patients experiencing more difficulties.