An older adult is diagnosed with Alzheimer's disease. The nurse knows that this diagnosis is made on the presence of which of the following? (Select all that apply.)

A. Fluctuation of symptoms over the course of a 24-hour period: Fluctuating symptoms are more characteristic of delirium or Lewy body dementia. Alzheimer’s disease typically presents with a consistent pattern of decline rather than abrupt or unpredictable changes in cognitive function throughout the day. B. A decline from previous level of functioning: Alzheimer’s disease involves a measurable decline in memory, reasoning, and daily functioning compared to the person’s prior baseline. This progressive loss interferes with independence and is one of the primary diagnostic indicators. C. An insidious onset: The onset of Alzheimer’s disease is slow and subtle, with early signs such as forgetfulness or difficulty completing familiar tasks. The gradual development of symptoms helps differentiate it from conditions like delirium, which have a sudden onset. D. A gradual decline in cognitive abilities: Alzheimer’s disease progresses steadily over time, leading to worsening impairments in memory, language, and executive function. The slow deterioration of cognitive abilities is a hallmark feature used to establish the diagnosis. E. The cognitive changes worsen in the evening hours: This phenomenon, known as “sundowning,” can occur in many types of dementia but is not a defining diagnostic criterion. While common in Alzheimer’s, it does not determine the diagnosis itself.