OBJECTIVES:To investigate whether delirium is associated with an unbalanced inflammatory response or a dysfunctional interaction between the cholinergic and immune systems. DESIGN: Cohort observational study. SETTING: General hospital orthopedic ward. PARTICIPANTS: One hundred one individuals aged 60 and older with no previous cognitive impairment undergoing elective arthroplasty. MEASUREMENTS: Incidence of postoperative delirium, plasma cholinesterase activity (acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE)) and inflammatory mediators (C-reactive protein (CRP), interleukin (IL)-1 beta, tumor necrosis factor alpha, IL-6, IL-8, IL-10) before and after surgery. RESULTS: Thirty-seven participants developed postoperative delirium and had greater production of CRP and proinflammatory to anti-inflammatory ratio after surgery. In participants with delirium, but not in controls, preoperative levels of plasma cholinesterase activity correlated with DCRP (AChE: ρ = 0.428, P = .008 and BuChE: ρ = 0.423, P = .009), DIL-6 (AChE: ρ = 0.339, P = .04), and DP/A ratio (AChE: ρ = 0.346, P = .04). CONCLUSION: Delirium was associated not only with an unbalanced inflammatory response, but also with a dysfunctional interaction between the cholinergic and immune systems. Comprehensive understanding of the relationship between the cholinergic and immune systems is crucial to developing new insights into delirium pathophysiology and novel therapeutic interventions. J Am Geriatr Soc 2012.

plasma cholinesterase activity can be a useful candidate biomarker to identify subjects at greater risk of developing postoperative delirium.

Hypothalamic-pituitary-adrenal axis hyperresponsiveness and a less frequent suppression of the GH/IGF-1 axis in response to acute stress are possibly involved in delirium pathophysiology.