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.

Between January 1988 and December 1989, 1,600 autopsies were performed at Huddinge University Hospital, representing approximately 40% of the 4,000 deceased patients. In 40% (647) of the autopsy cases, patients showed clinical signs of CNS dysfunction.

Of these cases, 58% (380) were subject to neuropathological evaluation, including both macro- and microscopic examination. Only macroscopic examination by general pathologists was performed on the remaining cases. Clinical signs of dementia were seen in 10% (169 cases) of the autopsied patients. Neuropathological evaluations were performed on 70% (118) of these patients. Of these, 60% (70) showed degenerative changes and 36% (43) vascular alterations. Macroscopic examinations alone were performed in 30% of the cases. Of these, signs of severe cortical atrophy were seen in 21%, vascular lesions in 12%, and no macroscopic changes in 67%. The completeness of clinical and postmortem examinations of the 169 demented patients was variable. Approximately 40% of the patients lacked any diagnostic decision. In approximately 50% of the cases with diagnostic decision, the clinical diagnosis correlated with the histopathological diagnosis. This low correlation between the clinical diagnosis and the exact nature of the disease was primarily based on the variable completeness of the clinical examinations. In order to improve this situation, it is important to perform both a complete clinical investigation and a neuropathological verification of the nature of the disease.

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.

The authors report preliminary data from a psychological autopsy study of completed suicide in late life. Sixteen of 18 victims had diagnosable psychopathology, most commonly major depression of late onset. Symptoms manifest prior to death are described and directions for future investigation discussed. The psychological autopsy is shown to be a viable method for studying suicide in the elderly.

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.

A thorough neuropathological analysis of several hundred cases from a prospective dementia study shows degenerative disorders such as dementia of Alzheimer type (DAT) and frontal lobe dementia (FLD) of non-Alzheimer type to be the prevailing disorders.

The pattern of basic changes relatable to neuronal atrophy in DAT correlates better to functional parameters and symptomatology than do senile plaques and neurofibrillary tangle density and distribution. The etiological or pathogenetic role of amyloid and of a cholinergic deficit also remains unclear. The dominating disease pattern may be blurred by confounding additional alterations with more pronounced frontal case pathology, as found in a limited number of cases. Another and much more common factor is structural white matter attenuation associated with cerebrovascular pathology as well as frank infarctions in a smaller but still important number of DAT cases. The concurrence of degenerative and other brain changes each at subthreshold levels may cause signs and symptoms of a dementia difficult to classify.

Frontal lobe dementia of non-Alzheimer type, the next most common dementing degenerative disorder, displays only the basic changes found in DAT but derives its separate clinical profile from the frontal predominance of lesions. It may be confounded with Pick's disease and others possibly belonging to the same group, but also with frontally projected dementias due to lesions ranging from thalamic infarcts to brain stem afflictions.

The topographic pattern of lesions rather than the structural details forms a useful basis for a clinical classification of the dementing disorders.

The effects of hospitalization on affective status were assessed by an original protocol in 214 consecutive elderly patients (mean age=78.3+/−5.0 years, range=70–92 years). Psychological decompensation was significantly related to length of stay (p<0.01) and drug use (p<0.05) and unaffected by sex, marital status, prior living place, diagnostic category. Affective status and functional status were directly correlated (p<0.0001), although in 51% of medical patients the affective status worsened or remained unchanged despite improved physical function. Improvement in affective status occurred more frequently in surgical patients (p<0.001) due to psychological improvement following surgery. Physicians providing medical and surgical care for geriatric patients must remain aware of the patients' emotional response to hospitalization and illness, given the accompanying risk for psychological decompensation.

The Max Planck Institute for Psychiatry (MPIP; Director: Florian Holsboer, M.D., Ph.D.) is a clinical research institute which serves psychiatric inpatients and several outpatient clinics (e.g., lithium clinic, memory clinic, anxiety disorder clinic, neuroleptic clinic). Affiliated with the Krankenhaus München-Schwabing, the largest general hospital in Bavaria (approximately 1,400 beds), the MPIP provides neurological and psychiatric consultation services for this center. According to the scientific concept envisioned by the first director of the MPIP, Emil Kraepelin, the Clinical Institute runs numerous on-site, state-of-the-art laboratories for basic research (molecular biology, neuroendocrinology, neuropharmacology, electrophysiology, neuropsychology, brain imaging) in order to bridge the gap between preclinical and clinical scientific activities.

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.