Relationship between apathy and cognitive dysfunctions in de novo untreated Parkinson's disease: a prospective longitudinal study

Background and purpose: Apathy may be either a symptom of major depression or a behavioral disturbance occurring in concomitance with depression or alone in Parkinson's disease (PD). The aim of the present study was to determine the progression of cognitive impairment in drug-naïve untreated PD patients with or without clinically significant apathy.

Methods: Sixty-two PD patients with a disease duration <2 years and without history of present or past therapy with pro-dopaminergic agents were included and underwent the Apathy Evaluation Scale (S-AES), a clinical interview based on diagnostic criteria for apathy and a comprehensive neuropsychological battery to assess memory, frontal functions and visuospatial functions. Two years after the first assessment, all patients were re-evaluated on the S-AES, a clinical interview and neuropsychological tests.

Results: According to the cut-off value of the S-AES and diagnostic criteria for apathy, eight patients experienced apathy at both baseline and follow-up (A+A+), nine patients had apathy only at follow-up (A-A+), 37 patients never experienced apathy (A-A-) and eight patients showed apathy at the baseline only (A+A-). Cognitive performance significantly declined in all four groups. At both baseline and follow-up A+A+ performed worse than A-A- on visuospatial and frontal tests; A-A+ had lower scores than A-A- on the interference task of the Stroop test (IT-ST). Regression analysis showed that poor performance on the IT-ST at baseline was the only independent predictor of onset of apathy at follow-up.

Conclusions: The results indicated a relationship between apathy and dysexecutive syndrome in early PD. Reduced scores on the IT-ST may predict development of apathy in PD patients.