Biomarkers of postoperative delirium and cognitive dysfunction

Neuroinflammatory challenges compromise neuronal function in the aging brain: Postoperative cognitive delirium and Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease that targets memory and cognition, and is the most common form of dementia among the elderly. Although AD itself has been extensively studied, very little is known about early-stage preclinical events and/or mechanisms that may underlie AD pathogenesis. Since the majority of AD cases are sporadic in nature, advancing age remains the greatest known risk factor for AD. However, additional environmental and epigenetic factors are thought to accompany increasing age to play a significant role in the pathogenesis of AD. Postoperative cognitive delirium (POD) is a behavioral syndrome that primarily occurs in elderly patients following a surgical procedure or injury and is characterized by disruptions in cognition. Individuals that experience POD are at an increased risk for developing dementia and AD compared to normal aging individuals. One way in which cognitive function is affected in cases of POD is through activation of the inflammatory cascade following surgery or injury. There is compelling evidence that immune challenges (surgery and/or injury) associated with POD trigger the release of pro-inflammatory cytokines into both the periphery and central nervous system. Thus, it is possible that cognitive impairments following an inflammatory episode may lead to more severe forms of dementia and AD pathogenesis. Here we will discuss the inflammation associated with POD, and highlight the advantages of using POD as a model to study inflammation-evoked cognitive impairment. We will explore the possibility that advancing age and immune challenges may provide mechanistic evidence correlating early life POD with AD. We will review and propose neural mechanisms by which cognitive impairments occur in cases of POD, and discuss how POD may augment the onset of AD.

Pyrrolidine Dithiocarbamate Prevents Neuroinflammation and Cognitive Dysfunction after Endotoxemia in Rats

Systemic inflammation, for example as a result of infection, often contributes to long-term complications. Neuroinflammation and cognitive decline are key hallmarks of several neurological conditions, including advance age. The contribution of systemic inflammation to the central nervous system (CNS) remains not fully understood. Using a model of peripheral endotoxemia with lipopolysaccharide (LPS) we investigated the role of nuclear factor-κB (NF-κB) activity in mediating long-term neuroinflammation and cognitive dysfunction in aged rats. Herein we describe the anti-inflammatory effects of pyrrolidine dithiocarbamate (PDTC), a selective NF-κB inhibitor, in modulating systemic cytokines including tumor necrosis factor (TNF)-α and interleukin-1β (IL-1β) and CNS markers after LPS exposure in aged rats. In the hippocampus, PDTC not only reduced neuroinflammation by modulating canonical NF-κB activity but also affected IL-1β expression in astrocytes. Parallel effects were observed on behavior and postsynaptic density-95 (PSD95), a marker of synaptic function. Taken together these changes improved acute and long-term cognitive function in aged rats after LPS exposure.

Improved cognitive flexibility after aortic valve replacement surgery

OBJECTIVES

Aortic valve replacement (AVR) surgery is associated with potential risk to cerebral injury. On the other hand, improved cardiovascular functioning after the surgery may have positive impact on brain health. The aim of this preliminary study was to investigate the impact of AVR surgery on cognition, specifically on higher cognitive control functions, i.e. executive functions, that are typically implicated in cognitive decline due to vascular origin.

METHODS

Patients (n = 16) undergoing elective AVR surgery due to aortic stenosis were recruited and their cognitive performance was assessed using a computer-based Executive Reaction Time (RT) test. Testing was performed 1 day prior to AVR surgery and ∼3 months after the surgery. In addition, the Behavior Rating Inventory of Executive Function-Adult Version (BRIEF-A) was used to assess everyday challenges in executive functions and self-regulation. Patient's postoperative test results were compared with each patient's preoperative results to determine changes in executive functions.

RESULTS

Subjects' overall cognitive performance improved after AVR surgery. After surgery, patients responded in the Executive RT test more accurately with the same response speed (change from 297 to 298 ms). Their overall probability to commit an error (total errors) was reduced by 47%, reflecting improved executive functions in general (OR = 0.53, 95% CI = 0.46-0.59, error rate change from 44.8 to 28.0%). Furthermore, one key component of executive functions, inhibitory control, was improved after AVR surgery. This was seen in reduced probability of failing to withhold a response, i.e. making a commission error, by 89% (OR = 0.11, CI = 0.08-0.16, error rate change from 11.8 to 2.6%). The probability of missing a response was reduced by 48%, reflecting improved attention (OR = 0.52, 0.44-0.64, error rate change from 18.1 to 11.0%). No statistically significant differences in BRIEF-A scores were found.

CONCLUSIONS

There was a marked improvement in cognitive performance following AVR surgery, specifically in executive control functions indicating improved cognitive flexibility. Cognitive improvement, as opposed to the typical trajectory of cognitive decline in an elderly population with vascular disease, emphasizes the importance of these results and points to AVR surgery as having potential benefits on brain health in general.

CLINICAL TRIALS IDENTIFIER

NCT01953068. https://www.clinicaltrials.gov/ct2/show/NCT01953068?term=NCT01953068&rank=1.

Comparison of cognitive and neuropsychiatric profiles in hospitalised elderly medical patients with delirium, dementia and comorbid delirium-dementia

OBJECTIVES

Differentiation of delirium and dementia is a key diagnostic challenge but there has been limited study of features that distinguish these conditions. We examined neuropsychiatric and neuropsychological symptoms in elderly medical inpatients to identify features that distinguish major neurocognitive disorders.

SETTING

University teaching hospital in Ireland.

PARTICIPANTS AND MEASURES

176 consecutive elderly medical inpatients (mean age 80.6 ± 7.0 years (range 60-96); 85 males (48%)) referred to a psychiatry for later life consultation-liaison service with Diagnostic and Statistical Manual of Mental Disorders (DSM) IV delirium, dementia, comorbid delirium-dementia and cognitively intact controls. Participants were assessed cross-sectionally with comparison of scores (including individual items) for the Revised Delirium Rating Scale (DRS-R98), Cognitive Test for Delirium (CTD) and Neuropsychiatric Inventory (NPI-Q).

RESULTS

The frequency of neurocognitive diagnoses was delirium (n=50), dementia (n=32), comorbid delirium-dementia (n=62) and cognitively intact patients (n=32). Both delirium and comorbid delirium-dementia groups scored higher than the dementia group for DRS-R98 and CTD total scores, but all three neurocognitively impaired groups scored similarly in respect of total NPI-Q scores. For individual DRS-R98 items, delirium groups were distinguished from dementia groups by a range of non-cognitive symptoms, but only for impaired attention of the cognitive items. For the CTD, attention (p=0.002) and vigilance (p=0.01) distinguished between delirium and dementia. No individual CTD item distinguished between comorbid delirium-dementia and delirium. For the NPI-Q, there were no differences between the three neurocognitively impaired groups for any individual item severity.

CONCLUSIONS

The neurocognitive profile of delirium is similar with or without comorbid dementia and differs from dementia without delirium. Simple tests of attention and vigilance can help to distinguish between delirium and other presentations. The NPI-Q does not readily distinguish between neuropsychiatric disturbances in delirium versus dementia. Cases of suspected behavioural and psychological symptoms of dementia should be carefully assessed for possible delirium.