The Diagnosis of Delirium Superimposed on Dementia: An Emerging Challenge

Abstract

Delirium occurring in patients with dementia is referred to as delirium superimposed on dementia (DSD). People who are older with dementia and who are institutionalized are at increased risk of developing delirium when hospitalized. In addition, their prior cognitive impairment makes detecting their delirium a challenge. The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition and the International Statistical Classification of Diseases and Related Health Problems, 10th Revision are considered the standard reference for the diagnosis of delirium and include criteria of impairments in cognitive processes such as attention, additional cognitive disturbances, or altered level of arousal. The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition and the International Statistical Classification of Diseases and Related Health Problems, 10th Revision does not provide guidance regarding specific tests for assessment of the cognitive process impaired in delirium. Importantly, the assessment or inclusion of preexisting cognitive impairment is also not addressed by these standards. The challenge of DSD gets more complex as types of dementia, particularly dementia with Lewy bodies, which has features of both delirium and dementia, are considered. The objective of this article is to critically review key elements for the diagnosis of DSD, including the challenge of neuropsychological assessment in patients with dementia and the influence of particular tests used to diagnose DSD. To address the challenges of DSD diagnosis, we present a framework for guiding the focus of future research efforts to develop a reliable reference standard to diagnose DSD. A key feature of a reliable reference standard will improve the ability to clinically diagnose DSD in facility-based patients and research studies.

Keywords: Alzheimer disease; Delirium; Lewy Body dementia; delirium superimposed on dementia; dementia; diagnosis.

Fig. 1

Cognitive domains and arousal. Different cognitive domains are affected in dementia, but the ability to engage cognition depends on the degree of arousal. In the radar plot to the left of the figure, this particular individual has almost normal arousal, perhaps being somewhat hyperalert (dashed circle signals “normal” arousal). With the onset of delirium, most cognitive domains deteriorate as arousal decreases (degree of arousal = dotted red circle) as could be the case given hypoactive delirium (radar plot to the right). In this constellation of an individual having shown cognitive impairment, including attention, prior to delirium, it is especially challenging to adequately test for specific change in any one of multiple attentional domains (marked 1). It is, moreover, as difficult to determine the time of onset given that change is not from a nonimpaired state (marked 2; the solid black line on the timeline signals the fluctuating degree of cognitive impairment, in close relationship to the severity of delirium symptoms), not knowing how severe the baseline impairment (dotted red line on the timeline) actually was (marked 3).

Fig. 2

The challenge of delirium across different types of dementia and possible overlap with behavioral and psychological symptoms of dementia (BPSD). AD, Alzheimer dementia; DLB, dementia with lewy bodies; VaD, vascular dementia; PD, Parkinson dementia.