Using the presence of visual hallucinations to differentiate Parkinson's disease from atypical parkinsonism

Objectives: Visual hallucinations (VH) occur frequently in Parkinson's disease (PD) and dementia with Lewy bodies (DLB) and are much less common in other bradykinetic rigid syndromes. Pathological series suggest that the presence of VH is highly specific for Lewy body pathology. To address the issue of diagnosis in patients with parkinsonism, we developed instructions for a structured interview (Queen Square Visual Hallucination Inventory (QSVHI)), capable of rapidly screening for VH in the outpatient setting. Methods: 181 consecutive patients from a specialist movement disorders clinic were tested (115 with PD, 23 with progressive supranuclear palsy (PSP), 9 with multiple system atrophy (MSA), 5 with vascular parkinsonism, 19 with unclassifiable parkinsonism (UP) and 8 others), and 15 selected patients from other clinics and 14 neurologically normal controls. The characteristics of hallucinators and non-hallucinators were compared and the sensitivity, specificity and predictive values of VH for a clinical diagnosis of PD calculated. Results: Screening questions identified VH in only 38% of patients with PD. The QSVHI identified VH in 75% of patients with PD and 47% of those with UP. The specificity of VH identified by the QSVHI for PD was 91%, sensitivity was 62%, positive predictive value was 95% and negative predictive value was 48%. Conclusions: The QSVHI appears to be a sensitive method for identifying VH in a movement disorders clinic. VH occurred predominantly in PD and very rarely in PSP and MSA. Among patients with unclassifiable or undetermined parkinsonism, the presence of VH should be considered a red flag for underlying Lewy body pathology.