Social cognitive impairment in early Parkinson's disease: A novel "mild impairment"?

INTRODUCTION: Social cognition (SC) deficit has recently been described in the early stages of Parkinson's disease (PD), but findings remain unclear. Our objective was to determine the frequency of SC impairment in newly-diagnosed PD patients and whether it is independent of Mild Cognitive Impairment (MCI). METHODS: We enrolled 109 patients with idiopathic PD diagnosed within the previous four years (ICEBERG cohort) and 39 healthy participants. SC was evaluated using the Mini-Social Cognition and Emotional Assessment (Mini-SEA) that allows a multi-domain assessment of SC. Relationships between SC and clinical characteristics, global cognitive efficiency, mood, anxiety, apathy and impulse control disorders, were also evaluated. RESULTS: 30% of patients had significant socio-emotional impairment. Moreover, SC deficit in isolation was 3.5 times more frequent than MCI in isolation (20.2% vs 5.5% respectively). Both emotion identification and Theory of Mind were impaired compared to healthy participants. No effect of age, level of education, disease severity, dopamine replacement therapy, or global cognitive efficiency were found. Only scores on the Frontal Assessment Battery were correlated with SC abilities. CONCLUSION: SC impairment is frequent in early PD and should be given more consideration. It often occurs in the absence of any other cognitive disorder and may represent the most common neuropsychological deficit in early-stage PD. In line with the definition of PD-MCI criteria, we consider the addition of a sixth MCI sub-type termed "Mild Social Cognition Impairment (MSCI)". Further studies are required to validate the addition of this new MCI domain.