We are grateful to Nancy Miller, Zbigniew Lipowski, and Barry Lebowitz for their outstanding work as guest editors of this issue of International Psychogeriatrics. These papers were stimulated by a special meeting of the National Institute of Mental Health (NIMH). They are authored by Americans and Canadians and are followed by discussions and critiques from experts in Europe, Australia, and Asia. This format is a novel one, but one which presents many exciting possibilities.

While there is little question that advancing chronological age is intimately implicated in the brain's enhanced vulnerability to acute confusional states, the nature and dynamics of this relationship, until recently, have managed to escape sustained empirical scrutiny. Despite the fact that the syndrome has been described in the medical literature for over 2,000 years, despite the presence of many anecdotal reports on delirium in the clinical literature, and despite its long-rooted association with high rates of morbidity and mortality in senescence, surprisingly little hard data has been collected regarding distribution of the syndrome in the general population, critical aspects of differential diagnosis, the spectrum of syndromal phenomenology, or the nature of clinical course and outcome. Additionally, many questions regarding etiology, pathophysiology, and pathology have received less than adequate research attention.

The development of the concept of delirium spans nearly 2,500 years. Its core clinical features were recognized at least as early as the 16th century, while its management reflected a humane approach from the beginning of the modern era. In the 19th century delirium became linked with the concepts of disordered consciousness and confusion, but these two terms were also used in regard to certain functional mental disorders. The most important contribution in this century was the work of Engel, Romano, and associates, who postulated that the syndrome was due to reduction in brain metabolic rate, as reflected in slowing of the EEG background activity. These and other developments are discussed in this article. A list of proposed research priorities is included.

“Delirium” is a reversible confusional state. It results from widespread but reversible interference with the function of cortical neurons, as documented by diffuse slowing on EEG and decreases in cerebral metabolic rate. Delirium can be due to impairments in neuronal metabolism, in neurotransmission (notably cholinergic), or in input from subcortical structures. Engel and Romano (1959) formulated delirium and dementia as the two poles of a spectrum of “cerebral insufficiency,” with delirium resulting from reversible functional impairment and dementia from irreversible anatomic damage. So many disorders can precipitate delirium that the differential diagnosis tests every facet of one's knowledge of medicine. With aging, both normative changes in the brain and the increasing incidence of brain diseases predispose to the development of delirium. The brain damage responsible for a dementia can sensitize to the development of a superimposed delirium.

While all delirious patients have clouding of consciousness (alteration of attention) and cognitive dysfunction, the level of alertness of different patients may range from stuporous to hyperalert. We, therefore, developed an analog scale to rate the alertness of delirious patients, and a separate scale to rate the severity of their clouding of consciousness. Based on these scales, patients were categorized overall as relatively “activated” (relatively alert despite clouding of consciousness), or “somnolent” (relatively stuporous along with clouding of consciousness). Cognitive function was estimated using the Mini-Mental Status Exam. Separate ratings were made of hallucinations, delusions, illusions, and agitated behavior. Activated and somnolent patients had similar ages, overall severity of delirium, and Mini-Mental Status Exam scores. Activated patients, however, were more likely to have hallucinations, delusions, and illusions than somnolent patients, and were more likely to have agitated behavior. Patients with hepatic encephalopathy were more likely to have somnolent delirium, while patients with alcohol withdrawal appeared more likely to have activated delirium. These data indicate that phenomenologic subtypes of delirium can be defined on the basis of level of alertness. These subtypes are validated in part by their differing associations with symptoms unrelated to alertness. These subtypes may have different pathophysiology, and thus, potentially different treatments.

This paper provides a review of research issues and findings on the epidemiology of delirium. Despite the fact that research on this important geriatric syndrome has been conducted for many decades, several methodological issues make it difficult to compare findings across studies. In this paper we first discuss broadly methodological issues related to diagnosis, case-finding, and populations studied. We next review data on the occurrence and consequences of the syndrome. A discussion of the design and preliminary results of the Commonwealth-Harvard Study of Delirium in Elderly Hospitalized Patients documents both how we responded to the methodological issues outlined and how these choices influenced our findings. We conclude with a discussion of the needs for further research on the epidemiology of delirium.

The 1981 East Baltimore Mental Health Survey, part of the Epidemiological Catchment Area (ECA) program, provided data for the examination of the prevalence of delirium in the general adult population. From an original 3,841 households surveyed, 810 individuals were selected for psychiatric evaluation and, of these, 6 individuals were diagnosed as suffering from delirium. The estimated prevalence of delirium in the population was .4% and 1.1% among those 55 years of age and over. A comparison of these cases with cases of diagnosed dementia and individuals of the same age range who did not receive a psychiatric diagnosis found that those with a diagnosis of delirium suffer from a greater number of medical conditions, take more prescribed medications, and have a higher level of physical disability.

Organic mental disorders with cognitive impairment constitute an important medical and public health problem in elderly people. The emergence of severe acute psychiatric manifestations of delirium as a consequence of structural brain disease or cerebral dysfunction related to some other physical illness is well known in clinical practice. After a long period of nosological inconsistency, the DSM-111, and now the DSM-111-R, present operational diagnostic criteria for delirium emphasizing the cognitive symptoms of the disorder. At the same time different psychomotor symptoms in, for example, hyperkinetic, mixed, or silent delirium are also being recognized. In addition, many clinical studies have illustrated the wide variation in predisposing, precipitating, and sustaining factors for delirium, thus providing a basis for etiological hypotheses.

This prospective study determined the incidence and prevalence of delirium in 235 consecutive subjects over age 70 admitted to a general medicine hospital service. The DSM-III criteria for delirium were operationalized. Using accepted screening procedures, patients were referred for evaluation by a psychiatrist who determined whether delirium was present by applying explicit operational definitions to each of the DSM-III criteria. Data on presence and severity of each of the DSM-III symptoms were recorded. Analysis of these data indicates that the DSM-III criteria describe a discrete, recognizable syndrome. However, some of the symptoms are more specific than others in identifying the syndrome in this population.

This paper reviews the historical development of the American Psychiatric Association's Diagnostic and Statistical Manual. It presents some of the issues that the clinician has found difficult in applying DSM-III and DSM-III-R criteria for delirium. In addition it introduces some options for DSM-IV criteria for delirium based on several empirical studies. These options should be studied and debated carefully over the next year because in part, they represent radical departures from existing diagnostic criteria for delirium.

The concept of delirium has gone through a major transformation in German-speaking psychiatry. In the traditional German-speaking literature, the concept was defined in very broad terms, partially corresponding to our present concept of psychosis. Today, the term is usually interpreted in terms of Bonhoeffer's “acute exogenous reaction types” which are classified under the reversible psychoses with “lowered consciousness”; the reversible (acute) organic psychoses are subdivided into those with and those without disturbance of consciousness.

The EEG is a useful and, at times, an essential test in the evaluation of delirium. In most patients with delirium, the EEG will show diffuse slowing and thus is helpful in differentiating organic etiologies from functional, psychiatric disorders. The degree of the EEG changes correlates with the severity of the encephalopathy so that the EEG may be used to help monitor therapy. In some delirious patients, the EEG may indicate whether the patient is suffering from focal, rather than global, impairment. Furthermore, the EEG is the only test that can identify an ongoing epileptic state (e.g., nonconvulsive status epilepticus) as being responsible for the clinical picture of confusion. Other electrophysiological tests that may prove helpful in the evaluation of delirium, such as computerized EEG spectral analysis, topographic brain mapping, and sleep studies, are briefly reviewed.

It has long been known that the conventional electroencephalogram (EEG) is a useful tool in the evaluation of delirium. There are moderate correlations between the amount of slowing seen on EEG and the degree of confusion or level of arousal observed among delirious patients. The usefulness of the EEG for assessment and diagnosis in this area has been limited, however, by: (a) difficulties in assessing the significance of slow-wave activity, (b) problems in detecting changes in relative EEG power, and (c) the logistical problem of lengthy recording sessions with agitated patients. This article selectively reviews the development of quantitative EEG methods and presents preliminary data from an ongoing longitudinal study of the use of these methods among elderly delirious patients. There has been little work done in applying quantitative methods to the study of delirium, and no work done that has systematically compared conventional EEG analysis to quantitative analysis. Delirium shares electrophysiological characteristics with other organic mental syndromes, however, where quantitative EEG has been shown to be useful. Furthermore, analysis of digital EEG data is inherently superior to visual inspection in assessing the distribution of EEG power among different frequency bands. Previous studies, as well as data presented here, suggest that quantitative EEG is a clinically useful supplement to the conventional EEG for the assessment of elderly patients with delirium.

The central nervous system electrical potentials recorded by the EEG are sensitive to alterations in the levels of consciousness and attention (Mesulam, 1986). Thus it is understandable that previous studies on delirious patients using routine EEGs have shown an increase of slow-wave activity and slowing and disruption of the normal alpha rhythm (Romano & Engel, 1944). At present, the electrocephalogram is widely accepted as a valuable ancillary laboratory procedure for diagnosis and serial evaluation of delirium, as EEG changes often accompany delirium.

Over the past several decades, numerous investigators have studied the syndrome of delirium. Researchers have relied on a number of different case finding methods to detect the syndrome. This paper provides an overview of instruments used in studies of delirium. We assess the validity and reliability of these instruments and compare the advantages and disadvantages of the different methods. We then present the rationale for the development of the Delirium Symptom Interview, an instrument constructed for use in the Commonwealth-Harvard Study of delirium in elderly hospitalized patients.

Ceiling effects limit the utility of many established brief cognitive screening tests for detecting and measuring mild delirious states and prodromal disorders. The High Sensitivity Cognitive Screen (HSCS) (Faust & Fogel, 1989), a bedside test taking approximately 25 minutes to administer, may overcome this limitation. The test consists of a selection of moderately difficult items testing six major domains of neuropsychological performance: memory, language, attention/concentration, visual/motor, spatial, and self-regulation and planning. Reliability is adequate, and two separate concurrent validity studies show accuracy rates of 93% and 87% in classifying the overall result of comprehensive neuropsychological testing. HSCS performance is highly correlated with EEG results in medical psychiatric inpatients, and with functional status in HIV-infected community-dwelling subjects. The brevity and convenience of the HSCS and related instruments make them particularly useful in studies of elderly and chronically ill subjects.

Current approaches to the diagnosis of delirium are based upon the recognition of symptoms that emerge in the pathological state. As an alternative, we propose an approach to case identification for research purposes based on the recognition of significant changes in the cognitive or cerebral state of the individual patient. Categorical change can be defined using prediction intervals calculated from repeated measures on a population of medically stable subjects. Data from subjects enrolled in a prospective study of delirium in a long-term care population were utilized to calculate prediction intervals for the Mini-Mental Status Examination and for measures of the electroencephalographic background frequency as obtained with a two-channel microprocessor-based EEG device. Preliminary findings support the validity of this quantitative approach for defining changes in brain state. Future research should evaluate both cognitive and electrophysiological techniques for monitoring vulnerable patients.

Characteristics of instruments developed by nurses for use in evaluating delirium/acute confusional states include relative emphasis on observable behavior and the need to impose low respondent burden. Two instruments that have been most used by nurse researchers are described: The Confusion Rating Scale and the NEECHAM Confusion Scale. The former is based on observable behavior; the latter incorporates vital function and oxygen saturation measurements that may serve as early warning sings of impending delirium.

The papers devoted to the subject of delirium in this issue make significant contributions toward the more precise and reliable diagnosis of the syndrome for the purposes of scientific investigation and clinical practice.