International psychogeriatrics
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Delirium is often considered a global and nonspecific alteration in cerebral function. However, the recent clinical evidence for heterogeneity within the syndrome of delirium suggests that different systems of the brain may be important in different kinds of delirium. Some forms of delirium, such as anticholinergic toxicity and hepatic encephalopathy, may be caused by drugs or toxins acting on specific brain neurochemical systems. ⋯ Little is known about changes in these systems with aging. The well-known degeneration in cholinergic systems in Alzheimer's disease, and the sensitivity of individuals with Alzheimer's disease to anticholinergic toxicity, suggest a role of central cholinergic systems in anticholinergic delirium in demented patients. Further research into the involvement of the other systems in aging and delirium apparently would be fruitful.
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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. ⋯ 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.
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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. ⋯ 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.
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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). ⋯ 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.