This patient should undergo testing for concurrent illnesses. She has had an acute change in cognitive symptoms accompanied by fluctuating symptoms, inattention, and a depressed level of consciousness. This presentation is consistent with delirium, which should be recognized early and treated by correction of the underlying cause. Underlying cognitive impairment or dementia is a significant risk factor for delirium. The acute change in mental status experienced by this patient is unlikely to be due to worsening dementia, given that the disease course has been slowly progressive to this point. Features of inattention and a depressed level of arousal are not common in Alzheimer disease until late in the disease course. The initial evaluation should focus on ruling out the most common metabolic and infectious causes of delirium in older patients by obtaining a complete blood count, serum electrolyte and plasma glucose levels, liver chemistry and kidney function tests, urinalysis, and a chest radiograph. Additional tests should be tailored to the clinical presentation.

Initiation of quetiapine is premature in this patient. Immediate therapy should focus on identifying and treating the underlying cause of delirium. For agitation, nonpharmacologic interventions should be tried first, such as frequent reorientation, avoiding immobilization and catheterization, restoring normal sleep patterns, and minimizing disruptions in the environment. Only if these steps prove inadequate should treatment with dopamine antagonists be considered.

Although cholinesterase inhibitors, such as donepezil, may be associated with cholinergic adverse effects in some patients, these effects tend to occur shortly after starting the medication or increasing the dose. This patient has tolerated a stable dose of donepezil for at least 1 year, and so it would not be appropriate to attribute her acute delirium to this medication. Evaluation for another cause should be pursued.

Neuroimaging is not indicated in the immediate evaluation of this patient because the findings on neurologic examination were nonfocal. If the initial testing for concurrent illnesses is unrevealing, additional evaluation would include neuroimaging to rule out hemorrhage, territorial infarction, or mass lesion.