Cognitive dysfunction in drug induced parkinsonism (DIP)

Several studies have suggested that the presence of dementia increases the risk of developing DIP. However, these prior studies exclusively focused on the underlying conditions before the development of DIP and there are no studies about the characteristics and prognosis of the cognitive status associated with DIP. We investigate the cognitive impairments associated with DIP by comparing neuro-psychological test results in patients with Parkinson's disease (PD) and normal controls and the longitudinal outcome of cognition in DIP. The cohort in this study included 13 consecutive patients with DIP and 91 patients with PD; all subjects completed a clinical assessment, neuropsychological investigation, and magnetic resonance imaging of brain. All patients with DIP were followed closely for more than six months after withdrawal of the offending drug. The cognitive function in DIP was significantly worse than in controls for most domains; however, there were no significant differences found in the comparisons with the PD patients. In addition, the severity of motor impairment was in part associated with cognitive function. Some patients had transient and reversible cognitive impairment, similar to other Parkinsonian motor features, and others experienced persistence and eventual worsening of their cognitive dysfunction after discontinuation of the offending drug. The results of this study suggest that cognitive impairment in patients with DIP reflects the toxic/metabolic symptoms associated with the offending drug in addition to being a risk factor for DIP.