Factors associated with drug-induced visual hallucinations in Parkinson's disease

Visual hallucinations are common in medication-treated Parkinson's disease (PD) patients. Although their etiology is unknown several factors seem to be involved in their pathogenesis. The aim of this study was to identify possible risk factors and determine clinical characteristics associated with the development of visual hallucinations in PD.

166 consecutive patients fulfilling clinical criteria for PD were studied. During a semi-structured interview, demographic characteristics and clinical variables were recorded. Motor, cognitive and psychiatric status was also assessed. Patients with and without visual hallucinations were compared using non-parametric tests, and logistic regression was applied to significant data.

During the month before evaluation 20.4% of our patients experienced visual hallucinations (11.4% benign, 9% malignant). Logistic regression analysis identified three factors independently associated with visual hallucinations: long duration of Parkinson's disease, dementia, and disease severity as measured by the UPDRS total score.

Our findings indicate that apart from well established risk factors such as cognitive impairment and disease duration, disease severity is also important for the development of visual hallucinations in PD. Furthermore, the presence of bradykinesia and instability, the absence of tremor and the severity of rigidity and bradykinesia (limb and axial) may act as cofactors.