An Interdisciplinary Reappraisal of Delirium and Proposed Subtypes

Abstract

An interdisciplinary plenary session entitled "Rethinking and Rehashing Delirium" was held during the 2021 Annual Meeting of the Academy of Consultation-Liaison Psychiatry to facilitate dialog on the prevalent approach to delirium. Panel members included a psychiatrist, neurointensivist, and critical care specialist, and attendee comments were solicited with the goal of developing a statement. Discussion was focused on a reappraisal of delirium and, in particular, its disparate terminology and history in relation to acute encephalopathy. The authors endorse a recent joint position statement that describes acute encephalopathy as a rapidly evolving (<4 weeks) pathobiological brain process that presents as subsyndromal delirium, delirium, or coma and suggest the following points of refinement: (1) to suggest that "delirium disorder" describe the diagnostic construct including its syndrome, precipitant(s), and unique pathophysiology; (2) to restrict the term "delirium" to describing the clinical syndrome encountered at the bedside; (3) to clarify that the disfavored term "altered mental status" may occasionally be an appropriate preliminary designation where the diagnosis cannot yet be specified further; and (4) to provide rationale for rejecting the terms acute brain injury, failure, or dysfunction. The final common pathway of delirium appears to involve higher-level brain network dysfunction, but there are many insults that can disrupt functional connectivity. We propose that future delirium classification systems should seek to characterize the unique pathophysiological disturbances ("endotypes") that underlie delirium and delirium's individual neuropsychiatric symptoms. We provide provisional means of classification in hopes that novel subtypes might lead to specific intervention to improve patient experience and outcomes. This paper concludes by considering future directions for the field. Key areas of opportunity include interdisciplinary initiatives to harmonize efforts across specialties and settings, enhance underrepresented groups in research, integration of delirium and encephalopathy in coding, development of relevant quality and safety measures, and exploration of opportunities for translational science.

Keywords: acute encephalopathy; altered mental status; delirium disorder; neuropsychiatric symptoms; pathophysiology; subtypes.

Figure 1:. Spectrum of mental states caused by acute encephalopathy

This figure represents both metabolic and toxic encephalopathies. Note that not all psychiatric syndromes due to medical conditions or states of substance intoxication or withdrawal necessarily qualify as an acute encephalopathy.

Figure 2:. Analogy of the different types of electrical grid disruption

Consider the many ways an electrical grid might malfunction. Each kind of disruption requires its own approach to restore grid activity. Repairs may require that the grid function at a lower power for a time (e.g., reduced level of arousal), that certain customers lose power temporarily (e.g., dysfunction in specific neurocognitive domains) or that the entire grid be reset (e.g., a restorative night’s rest). Some insults will cause irreversible damage (e.g., aging) whereas others cause only a temporary disruption of service (e.g., anesthesia). Adapted from public domain image from US Energy Information Administration.