Apathy, fatigue and quality of life in patients with Parkinson's disease

Parkinson’s disease (PD) is a chronic neurodegenerative disorder characterised by the presence of motor but also a number of non-motor symptoms (NMS). This study focuses on the NMS in PD, on the tools for their assessment, especially the Movement Disorder Society – Unified Parkinson’s DIsease Rating Scale (MDS-UPDRS) and on the relationships between different NMS and Quality of life (QoL). It also focuses on neuropsychiatric symptoms, including fatigue, apathy and depression, which have a high coincidence and can be easily misdiagnosed, on the associations between these NMS and their clinical determinants. One of the most important NMS in PD regarding QoL is fatigue, which has been previously associated most commonly with depression. Based on the presence of depression and excessive daytime somnolence, we have as first formulated the concept of primary and secondary fatigue, which presents different constructs in PD; therefore, future studies on the pathophysiology and/or treatment of fatigue should distinguish these concepts. Moreover, a similar relationship with depression, as seen in fatigue, can be found also in apathy; however, all of these symptoms have to be distinguished in PD. As found in our study, apathy is not related to the physical aspects of fatigue in either depressed or non-depressed patients, but we found it to be the only clinical determinant of mental aspects of fatigue in non-depressed PD patients