Various conditions that should be considered in the differential diagnosis of delirium are listed in Table 4.
Table 4. Differential Diagnosis of Delirium
(A) Drug-induced disorders in which delirium, or a state resembling it, is a component.
(B) Acute neurologic disorders that may present with delirium
(C) Other conditions that are also risk factors for the development of delirium
(D) Psychiatric disorders
(E) The intensive care unit syndrome, which is an altered emotional state, occurs in a highly stressful environment and may manifest itself as delirium.
Anticholinergics, together with a number of different drugs, may significantly contribute to the delirium onset, especially in elderly, demented persons (Gareri et al 2007). Side effects such as delirium, induced by anticholinergic drugs, are particularly severe in aging brain (Cancelli et al 2009).
Anticholinergic syndrome used to be common after general anesthesia because of the premedication with anticholinergic agents atropine and scopolamine. Because these agents are used infrequently, this syndrome occurs infrequently but may still occur due to anticholinergic effect of some general anesthetics. Therefore, this syndrome should still be considered in the differential diagnosis of delirium after anesthesia. It can be reversed by administration of physostigmine.
After drug-induced disorders, the next most important differential diagnosis is dementia. Delirium has an acute onset, whereas dementia develops slowly over a longer period. In uncomplicated dementia, consciousness remains essentially intact, whereas its impairment is an important feature of delirium. One of the features of dementia is short-term memory deficit in the absence of an attentional deficit before the disease progresses to impair long-term memory as well. In delirium, short-term memory deficit does not occur in the absence of attentional deficits, and there is no clear-cut progression to long-term memory deficits. A higher level term cognitive impairment that includes both dementia and delirium may be used if it is not possible to delineate delirium from dementia, which may coexist in a particular patient.
Clinical features common to delirium and schizophrenia are incoherent speech, disturbances of affect, delusions, and hallucinations. Delusions form a part of abnormal beliefs in schizophrenic patients, and hallucinations are usually auditory. Hallucinations in delirium are usually visual. Consciousness, memory, and attention are relatively unimpaired in schizophrenia as compared to delirium. There may be a difficulty in differentiating between delirium and an acute psychotic state where the patient may be confused and show signs of altered consciousness.