Anhedonia in Parkinson's disease: a systematic review of the literature.

Anhedonia, defined as lowered ability to experience physical or social pleasure, is a key symptom of several psychiatric illnesses. In this systematic review, we aimed to evaluate the role of anhedonia in Parkinson's Disease and its relationships with other clinical characteristics, dopamine dysfunction, and antiparkinsonian therapy. The database was selected using PubMed Services. Relevant journals were hand-searched, and the bibliographies of all the important articles were scrutinized to find additional publications. Fifteen studies assessed the topic of anhedonia in Parkinson's disease from 1984 to 2009 and mainly described it as a core symptom of depression in patients with Parkinson's disease. Some studies investigated the relationship between anhedonia and neuropsychological symptoms and found correlations with frontal lobe functions. Reports on the relationship between anhedonia and illness severity or motor symptoms are rather inconclusive. No definitive conclusions can be drawn because few studies have been published on this topic. Nevertheless, some evidence suggests that in Parkinson's disease anhedonia is a secondary phenomenon linked to depression, apathy severity, and frontal lobe dysregulation and that it could respond to antiparkinsonian treatment. Future studies of larger samples of patients are strongly required to definitively clarify the relationship between anhedonia and other clinical features, such as depression, anxiety, apathy, cognition, and motor status. Furthermore, more reliable tools and validated diagnostic criteria are necessary to assess anhedonia in patients with Parkinson's disease.