Neuropsychiatric symptoms are associated with dementia in Parkinson’s disease but not predictive of it

Background Neuropsychiatric symptoms in Parkinson’s disease (PD) may increase dementia (PDD) risk. The predictive value of these symptoms, however, has not been compared to clinical and demographic predictors of future PDD. Methods 325 PD participants completed baseline neuropsychiatric and MDS-Task Force Level II assessments. Of these, 195 non-demented individuals were followed-up over a four-year period to detect conversion to PDD; 51 developed PDD. ROC analysis tested associations between baseline neuropsychiatric symptoms and conversion to PDD. The probability of developing PDD was also modelled as a function of neuropsychiatric inventory (NPI) total score, PD Questionnaire (PDQ) hallucinations, PDQ anxiety and contrasted to cognitive ability, age and motor function. Leave-one-out information criterion was used to evaluate which models provided useful information when predicting future PDD. Results The PDD group experienced greater levels of neuropsychiatric symptoms compared to the PD-MCI and PD-N groups at baseline. Few differences were found between the PD-MCI and PD-N groups. Five neuropsychiatric measures were significantly, but weakly, associated with future PDD. The strongest was NPI total score: AUC=0.66 [0.55-0.76]. There was, however, no evidence that it contained useful out-of-sample predictive information of future PDD (delta ELPD=1.6 (SD 2.4)); Similar results held for PDQ hallucinations and PDQ anxiety. In contrast, cognitive ability (delta ELPD=35 (SD 8)) and age (delta ELPD=11 (SD 5)) provided useful predictive information of future PDD. Conclusions Cognitive ability and age strongly out-performed neuropsychiatric measures as markers of developing PDD within four years. Therefore, neuropsychiatric symptoms do not appear to be useful markers of PDD risk.