Relationship between depression and cognitive dysfunctions in Parkinson's disease without dementia

To explore the relationship between depression and cognitive impairment in non-demented PD patients, we evaluated neurological and neuropsychological asset in 65 patients with a diagnosis of major depressive disorder (dPD) according to DSM-IV criteria and 60 patients without depression (nPD). Compared with nPD patients, dPD patients had significantly higher scores on behavioral rating scales and performed worse on the Frontal Assessment Battery (FAB), Semantic Fluency Task, Copying Task (CT), and Stroop Test. Three dPD subgroups were identified based on the first two DSM-IV criteria: patients fulfilling criterion 1 (depressed mood; group 1); patients fulfilling criterion 2 (apathy/anhedonia; group 2); patients fulfilling criteria 1 and 2 (group 3). Patients of group 2 scored significantly lower than patients of group 1 on the CT, FAB and phonological fluency task. Patients of groups 2 and 3 scored significantly lower than nPD patients on visuoconstructional and frontal tasks. Similar results were obtained in dPD patients stratified in four subgroups based on cut-off scores of the Apathy Evaluation Scale and the Snaith Hamilton Pleasure Scale. In summary, PD patients with concomitant apathy and anhedonia may show more severe cognitive impairments. Since such patients are diagnosed to be affected by depression according to clinical DSM-IV criteria, we suggest that DSM-IV criteria may not distinguish an affective from a cognitive disorder in PD.