Hemiparkinsonism secondary to a vascular mesencephalic lesion is infrequent; these patients offer an exceptional opportunity to study neuropsychological alterations attributable to unilateral dopaminergic denervation, shedding light on the pathophysiology of cognitive disorders in early-stage idiopathic Parkinson's disease (PD). From the investigation of our case, we conclude that destruction of the right nigrostriatal pathway is accompanied by deficits in executive functioning and verbal/visual memory similar to those observed in many patients with early-stage idiopathic PD. The more complex neuropsychological dysfunction developed by other PD patients must therefore be related to the additional involvement of other brain structures. (JINS, 2013, 19, 1–6)
