Decreased platelet serotonin concentration in Alzheimer's disease with involuntary emotional expression disorder

• AD patients with IEED have low platelet 5-HT concentrations.
• Aggressive behavior in AD is not related with platelet 5-HT deficiency.
• IEED in AD could be associated with the changes in serotonergic system.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder manifested by progressive decline in cognitive functions. A variety of behavioral disturbances appear very often in AD which might be associated with altered function of serotoninergic system. The aim of the study was to determine platelet serotonin (5-HT) concentrations in 49 patients with AD (NINCDS-ADRDA and DSM-IV-TR criteria) subdivided in three groups: (a) patients with aggressive behavior, (b) patients with involuntary emotional expression disorder (IEED) and (c) patients without aggression or IEED (controls). Platelet 5-HT concentrations were measured using ELISA. Platelet 5-HT concentrations were significantly lower in patients with AD and co-existing IEED compared to AD patients with aggressive behavior or control patients. No significant difference in platelet 5-HT concentrations was found between patients expressing aggressive behavior and controls. Our results suggest disruptions in serotoninergic system in AD patients with comorbid IEED but not with aggressive behavior and support the presumption that platelet 5-HT concentration is a suitable and easy measured peripheral indicator of some behavioral and psychological symptoms of AD.