Hedonic tone and its mood and cognitive correlates in Parkinson's disease.
BACKGROUND
Anhedonia has been mainly reported as a symptom of depression and cognitive impairment in Parkinson's disease (PD) patients. Here, we investigated whether hedonic tone depends on depression and clarified its relationship with the cognitive performance of PD patients with different mood disorders.


METHODS
In 254 patients, we assessed hedonic tone using the Snaith-Hamilton Pleasure Scale, depression severity using the Beck Depression Inventory, and cognitive performances using the Mental Deterioration Battery. A structural psychiatric interview was used to diagnose major depressive disorder (MDD) and minor depressive disorder (MIND), according to the DSM-IV-TR criteria.


RESULTS
PD patients with diagnosis of MDD were more anhedonic than those with MIND and those without depressive disorders. Reduced hedonic tone correlated with depression severity in patients with MDD and no depressive disorders. In multivariate models that consider depression severity and cognitive performances together, anhedonia was related to increased depression severity and episodic memory (auditory-verbal learning) impairment, in patients with MDD and with increased depression severity and attention impairment in patients with no depressive disorders. In patients with MIND, anhedonia did not correlate with depression severity or any cognitive performance score.


DISCUSSION
Our findings suggest that anhedonia is related to depression severity and specific cognitive performances in patients with MDD and with no depressive disorder. By contrast, the reduced hedonic tone in patients with MIND is independent from depression severity and cognition. Thus, anhedonia in PD is a heterogeneous and multidimensional phenomenon and require investigation at different levels.