Cognitive correlates of hallucinations and delusions in Parkinson's disease

Hallucinations and delusions that complicate Parkinson's disease (PD) could lead to nursing home placement and are linked to increased mortality. Cognitive impairments are typically associated with the presence of hallucinations but there are no data regarding whether such a relationship exists with delusions.

We hypothesized that hallucinations would be associated with executive and visuospatial disturbance. An exploratory examination of cognitive correlates of delusions was also completed to address the question of whether they differ from hallucinations.

144 PD subjects completed a neuropsychological battery to assess cognition and the SAPS to examine psychosis. Correlational analyses assessed associations between hallucinations and delusions with cognitive domains.

48 subjects (33%) reported psychotic symptoms: 25 (17%) experienced hallucinations without delusions, 23 (16%) had symptoms dominated by delusions. Severity and/or number of hallucination subtypes were significantly correlated with lower scores in language, memory, attention, executive functioning, and visuospatial ability. Correlations with delusions were non-significant. Tests of differences in the size of the correlations between groups revealed a significant relationship between language and visuospatial performance with hallucinations.

Cognitive correlates of hallucinations and delusions appear to be different in PD, suggesting distinct pathogenic mechanisms and possibly anatomical substrates. Hence, delusions may not share the same associations with dementia as hallucinations. Since this is a new finding, further studies will be needed to confirm our results.