Delusions and hallucinations occur frequently in patients with Alzheimer’s disease (AD). They are also often correlated with accelerated cognitive decline and poorer outcomes. While neuroanatomical studies have revealed frontal gray-matter changes to be associated with the presence of delusions and changes in parietal and occipital regions with hallucinations, it is still unclear how psychosis affects the cognition of patients with AD. This study therefore aims to examine how the presence of delusions or hallucinations impacts the cognitive functioning of those with AD.

A total of 156 patients (79 women, M age = 77.82, M education = 14.21) diagnosed with Alzheimer’s disease (AD) participated in comprehensive neuropsychological assessment as part of outpatient neurology evaluations. 24% reported experiencing delusions, and 20% reported experiencing hallucinations. There were no differences in gender, age, or education between patients with AD who did and didn’t have either hallucinations or delusions, p = n.s. 

According to t-test analyses, patients with delusions performed significantly worse on MoCA, t(147) = 3.00, p < .01, BNT, t(145) = 2.23, p < .03, and WAIS-IV Similarities, t(145) = 3.03, p < .01, than those without delusions. They also had nonsignificant, but meaningful trends toward weaker scores on WAIS-IV Picture Completion, t(142) = 1.78, p = .07 and ROCF Copy, t(122) = 1.84, p = .07. Those experiencing hallucinations exhibited significantly lower scores on MoCA, t(147) = 2.86, p < .01, DKEFS Color Naming, t(129) = 2.07, p < .05, Trails A, t(140) = 4.45, p < .01, ROCF Copy, t(122) = 3.87, p < .01, and Trails B, t(131) = 3.33, p < .01, than those without hallucinations.

This suggests that delusions and hallucinations are associated with unique cognitive profiles among those with AD. Those with AD who experience hallucinations have significantly greater difficulties in gross cognitive functioning, visual processing speed, figure copying, and divided attention than those not experiencing hallucinations. Significantly greater problems in gross cognitive functioning, confrontation naming, visual perception, and abstract reasoning occur when delusions are present. Accounting for these differences are likely the frontal, temporal, and parietal alterations that engender hallucinations and delusions. These findings highlight the criticality of assessing for hallucinations and delusions during clinical interviews, and differentiating between these profiles is essential to improving patient outcomes. Moreover, interventions for offsetting decline corresponding to hallucinations and delusions may be most effective when targeting these specific cognitive abilities.