Review article
Defining delirium for the International Classification of Diseases, 11th Revision

https://doi.org/10.1016/j.jpsychores.2008.05.015Get rights and content

Abstract

Objective

The development of ICD-11 provides an opportunity to update the description of delirium according to emerging data that have added to our understanding of this complex neuropsychiatric syndrome.

Method

Synthetic article based on published work considered by the authors to be relevant to the definition of delirium.

Results

The current DSM-IV definition of delirium is preferred to the ICD-10 because of its greater inclusivity. Evidence does not support major changes in the principal components of present definitions but a number of key issues for the updated definition were identified. These include better account of non-cognitive features, more guidance for rating contextual diagnostic items, clearer definition regarding the interface with dementia, and accounting for illness severity, clinical subtypes and course.

Conclusion

Development of the ICD definition of delirium can allow for more targeted research and clinical effort.

Introduction

Acute disturbance of mental status in the context of illness, stress, or drug intoxication has been recognized as an entity for millennia. However, only with the development of clear definitions and diagnostic criteria has delirium begun to receive the clinical and research attention that it warrants. The syndromal nature of delirium means that diagnostic criteria are subject to testing and refinement as new data emerge. The past decade has witnessed considerable research activity relevant to delirium and as a consequence the task of updating the existing International Classification of Diseases (ICD) definition by the World Health Organization [1] provides an opportunity to develop the concept and address the shortcomings of the present definition according to data rather than mere expert opinion. This process must be sensitive to the current definition, so that existing research maintains generalisability, as well as allow closer alignment to the Diagnostic and Statistical Manual of Mental Disorders (DSM) systems. Moreover, developments in relation to the dementias also require that the interface between these connected disorders be addressed. Finally, an updated definition must be operationalized such that delirium can be reliably detected in clinical practice as well as research. The purpose of this article was to consider evidence that can inform the revision process for the definition of delirium for ICD-11 which is planned for publication in 2011.

Delirium does not have any pathognomic feature and instead the diagnosis is based upon characteristic symptoms occurring in a context that is highly suggestive. The definition of delirium must therefore combine key clinical symptoms and signs with required contextual items. Delirium is frequently comorbid with preexisting cognitive problems and occurs in the context of precipitating illness, other forms of stress (e.g., postoperatively), and drug intoxication. A challenge in definition is to account for this complex clinical picture that varies with causation and across treatment settings. Although delirium is a complex disorder, clinicians and researchers need criteria that are robust, reliable, objective, and as simple as possible. It is essential to have criteria that have utility in real-world settings, make diagnosis of milder and less obvious forms easy, but can identify those with poor outcome across different populations.

Section snippets

International Classification of Diseases, 10th Revision

The existing ICD-10 definition of delirium [1] includes different criteria for clinical and research use both of which include a broad range of features that capture the phenomenological complexity of the syndrome. It therefore contrasts with the DSM-IV[2] definition which does not mention characteristic features such as disturbances of sleep–wake cycle and motor activity. However, the ICD-10 criteria for delirium have not been preferred by researchers, partly reflecting the sizeable

Sources of information in determining delirium caseness

Making a diagnosis of delirium usually requires gathering information from multiple sources. A patient's mental status can be assessed by observation, interview, and formal cognitive testing. Further information regarding the course of any deficits is gleaned from the observer's knowledge of the patient, clinical notes, other staff, carers, etc. Specifying the type and quality of this information is important. Delirium presents special challenges here. Because delirium symptoms fluctuate, a

Attention as the core sign of delirium

For many centuries, the concept of delirium has included altered consciousness with generalized disturbance of higher cortical function. The extent to which all measurable elements of cognition should be affected and whether a primary cognitive domain is disproportionately impaired is less clear. Historically, clouding of consciousness has been emphasized, but this is a concept that lacks precision. Disturbed attention has become a cardinal feature of diagnostic criteria for delirium since DSM

Cognitive deficits in delirium

Delirium diagnosis currently also requires the demonstration of generalized cognitive disturbance which allows distinction from disorders with more discrete neuropsychological disruptions (e.g., dysmnesic syndromes, mood disorders, attention deficit disorders, etc.). ICD-10 mandates that disturbances of both memory and orientation be evident. Specifically, a disproportionate disturbance of immediate recall and recent memory with relatively intact remote memory is required. Phenomenological

Arousal and motor activity in delirium

Another important differentiating feature between delirium and dementia is arousal. Marked variations in arousal are a defining feature of dementia with Lewy bodies [19], but are not a common feature of other forms of dementia of mild to moderate severity. In contrast, patients with delirium are frequently drowsy or stuporous. When reduced arousal occurs in the context of acute illness, delirium is a likely diagnosis. In such circumstances the patient is usually not amenable to cognitive

Other neuropsychiatric features

Delirium typically includes a range of noncognitive neuropsychiatric symptoms. Some are almost invariably present (i.e., disturbances of motor activity and sleep–wake cycle occur in over 90% of cases of delirium) [7], [20]. However, these are relatively nonspecific symptoms that occur with great frequency across a range of neuropsychiatric syndromes and in nondelirious hospitalized elderly. For DSM-IV[21], it was concluded that the inclusion of sleep and motor disturbances would not add to the

The context of delirium symptoms

Although individual symptoms and signs are not specific to delirium, their combination and context are highly characteristic and are an important pointer when attempting to distinguish delirium from more chronic disorders such as dementia. Delirium is typically of acute onset and symptoms fluctuate over the course of the day. In ICD-10 diagnostic criteria for research, Criterion E mandates that “symptoms have rapid onset and show fluctuations over the course of the day.” However, many cases are

Aetiological attribution

Delirium is highly heterogeneous in its causation with typically three to four significant causes operating in parallel and/or sequentially over the course of an episode [7], [26], [27]. As such, single aetiology delirium is the exception rather than the rule. Although many accept that the aetiology of delirium contributes to clinical profile, convincing evidence that aetiology impacts upon phenomenological presentation and/or treatment needs remains lacking. Moreover, existing studies do not

Delirium and dementia

A major challenge is to create a delirium definition that improves recognition in clinical practice. A principal reason for poor detection is that delirium and dementia commonly co-exist especially in elderly patients where delirium is frequently misattributed to dementia symptoms [29]. In ICD-10, the presence of underlying dementia is emphasized as a subtype of delirium but the diagnosis of each is made separately. According to the ICD-10, the diagnosis of dementia cannot be established before

The duration, course, and severity of delirium

The course of delirium is highly variable, ranging from a short-lived disturbance lasting hours to days to a more persistent and often more severe deterioration that overlaps with dementia [23], [33]. The classical concept of delirium includes reversibility as a key element, although studies have highlighted that this is not the course for many elderly medical patients that develop delirium [34], [35]. The extent to which this reflects delirium's role as a harbinger of a previously silent

Clinical subtypes

Delirium is a highly heterogeneous syndrome and as such there may be utility in allocation of cases according to clinical subtypes. To date, most interest has involved subtyping according to motor activity alterations partly because of their high visibility and frequency (over 90% of deliria). Agitated-hyperalert vs. quiet-hypoactive variants of acute cognitive disturbances have been noted since ancient times as phrenitis and lethargicus, respectively. In more recent times, three motor variants

Syndromal vs. subsyndromal delirium

Recent studies have suggested that the presence of some features of delirium, but without sufficient features to meet DSM or ICD criteria or at a severity below diagnostic cut-off for delirium on diagnostic scales, may be associated with adverse outcomes [58], [59], [60]. These findings along with studies that have linked prognosis to individual symptoms [61] suggest that further clarification of the significance of individual features is required. In particular, these findings raise the

Conclusions

DSM-IV descriptions of delirium have good acceptance among both clinicians and researchers and future descriptions within ICD need to be better aligned. Where possible, changes should be according to available research rather than to expert opinion or other factors. There does not appear to be strong, formal evidence to support major changes in the key features outlined in current DSM definitions, but some elements of the syndrome could be better accounted for, especially disturbances of

Acknowledgments

AM was supported by an MRC Clinician Scientist Fellowship. The UK Medical Research Council and the University of Edinburgh provide core funding for the MRC Centre for Cognitive Ageing and Cognitive Epidemiology which supported AM.

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