Differential diagnosis of dementia, delirium and depression. Implications for drug therapy.
Dementia, delirium and depression are the 3 most prevalent mental disorders in the elderly. While dementia and depression are prevalent in the community, hospitals and nursing homes, delirium is seen most often in acute care hospitals. Much of the management of these syndromes is undertaken by primary care physicians rather than psychiatrists. Therefore, it is imperative that generalist physicians be adept at recognising, evaluating and managing patients with these syndromes. Because no diagnostic tests are pathognomonic of these syndromes, the differential diagnosis hinges on a careful clinical evaluation. The first step is to recognise which of the syndromes is present. Dementia is defined by a chronic loss of intellectual or cognitive function of sufficient severity to interfere with social or occupational function. Delirium is an acute disturbance of consciousness marked by an attention deficit and a change in cognitive function. Depression is an affective disorder evidenced by a dysphoric mood, but the most pervasive symptom is a loss of ability to enjoy usual activities. It is important to recognise that these syndromes are not mutually exclusive, as dementia frequently coexists with delirium and depression. Furthermore, physical diagnoses, such as chronic obstructive lung disease, congestive heart failure, stroke and endocrine disorders, are frequently associated with depressive symptoms. Given this, a comprehensive evaluation is mandatory. Laboratory tests are necessary to exclude concurrent metabolic, endocrine and infectious disorders, and drug effects. Imaging studies should be obtained selectively in patients with signs and symptoms, such as focal neurological findings and gait disturbances, which are suggestive of structural lesions: stroke, subdural haematoma, normal pressure hydrocephalus and brain tumours. Appropriate management involving pharmacological and nonpharmacological measures will result in significant improvement in most patients with these syndromes. Potentially offending drugs should be discontinued. In delirious patients the underlying illness must be treated concomitantly with the use of psychotropics, if necessary. Although no current medications have been shown to have a significant effect on the functional status of patients with the 2 most common causes of dementia, Alzheimer's disease and multi-infarct dementia, the management of concomitant illness in these patients may result in improved function for as long as a year. Tacrine, an anticholinesterase inhibitor, improves cognitive function slightly in selected patients with Alzheimer's disease over short periods. Finally, the treatment of depression with medications or electroconvulsive therapy (ECT) results in significant reductions in mortality and morbidity.