Clinical features Cognitive impairment

Dementia is an acquired and progressive cognitive decline in multiple areas; AD is one cause of dementia and the core clinical symptom of AD is cognitive impairment. However, as noted above, AD is clinically heterogeneous and includes diverse non-cognitive symptoms and inevitable functional impairment. Cognitive decline is manifested as amnesia, aphasia, agnosia, and apraxia (the 4As).

Amnesia

Memory loss in AD is early and inevitable. Characteristically, recent memories are lost before remote memories. However, there is considerable individual variation, with some patients able to recall specific and detailed events of childhood and others apparently having few distant memories accessible. With disease progression, even remote and emotionally charged memories are lost. The discrepancy between recent and remote memory loss suggests that the primary problem is of acquisition or retrieval of memory rather than a destruction of memory, and this is confirmed in early AD,(2) although as the disease progresses it is likely that all memory processes are impaired. Retrieval of remote memory is assumed to be preserved for longer because of rehearsal over life.

Aphasia

Language problems are found in many patients at presentation, although the language deficits in AD are not as severe as those of the frontotemporal degenerations (3) and may only be apparent on detailed examination. Word-finding difficulties (nominal dysphasia) are the earliest phenomena observed and are accompanied by circumlocutions and other responses, for example repetitions and alternative wordings. As the disorder progresses, syntax is affected and speech becomes increasingly paraphasic. Although harder to assess, receptive aphasia, or comprehension of speech, is almost certainly affected. In the final stages of the disorder, speech is grossly deteriorated with decreased fluency, preservation, echolalia, and abnormal non-speech utterances.

Agnosia

Patients with AD may have difficulty in recognizing as well as naming objects. This can have implications for care needs and safety if the unrecognized objects are important for daily functioning. One particular agnosia encountered in aD is the loss of recognition of one's own face (autoprosopagnosia). This distressing symptom is the underlying cause of perhaps the only clinical sign in AD—the mirror sign. Patients exhibiting this will interpret the face in the mirror as some other individual and respond by talking to it or by apparent fearfulness. Autoprosopagnosia can present as an apparent hallucinatory experience, until it is realized that the 'hallucination' is fixed in both content and space, occurring only when self-reflection can be seen.

Apraxia

Difficulties with complex tasks that are not due to motor impairment become apparent in the moderate stages of AD. Typically, difficulties with dressing or tasks in the kitchen are noticed first, but these are inevitably preceded by loss of ability for more difficult tasks. Strategies to avoid such tasks are often acquired as the disease progresses, and it is only when these fail that the dyspraxia becomes apparent.

Other cognitive impairments

There appear to be no cognitive functions that are truly preserved in AD. Visuospatial difficulties commonly occur in the middle stages of the disorder and may result in topographical disorientation, wandering, and becoming lost. Difficulties with calculation, attention, and cognitive planning all occur.

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