COGNITIVE SYMPTOMS

Impairment in cognitive function is the core feature of Alzheimer’s disease. Several areas of cognition may be affected and the degree of impairment varies with illness severity (Table 41.1).

Memory

Disturbance of memory is regarded as the hallmark of Alzheimer’s disease. Memory impairment is, however, not always the initial symptom. Affective symptoms may often precede memory disturbance⁵. It is important to note that the spouse or close relatives of most patients with Alzheimer’s disease are usually the ones who bring the memory deficits to clinical attention, not the patients themselves. Early memory symptoms heralding the onset of dementia include difficulty with the registration and retention of new information, leading to repeating questions or comments. There may also be difficulty manipulating stored information associated with working memory. Delayed spontaneous recall of recently acquired information is impaired in early stages⁶. Immediate recall, recognition and registration of information become increasingly affected with progression of illness. As these symptoms worsen, memory dysfunction affects daily function, which is important in differentiating dementia from memory decline associated with normal ageing. Individuals with early Alzheimer’s disease may develop difficulty recalling recent tasks, events, directions and appointments.

Those with advanced education or high intellectual reserve may be able to adapt for some time with minimal impact on their daily function. Some resort to memory cues, such as taking notes or keeping journals, to compensate for decline in memory. In moderate to severe stages, long-term memory becomes impaired. There may be inability to accurately recall details of familiar historic events and personal information, including names of family members, birthdays, special occasions or other aspects of declarative memory.

Language

Both oral and written impairments of language are found in Alzheimer’s disease. In the early stages, fluent dysphasia may predominate, often in a pattern similar to transcortical sensory aphasia. Characteristic deficits at this stage include diminished vocabulary and word finding difficulty. Individuals with early dementia often have difficulty selecting words and may lose track during conversations⁶. Word repertoire shrinks and use of language

Table 41.1 Cognitive symptoms associated with Alzheimer’s dementia

becomes more simplistic, often described as circumlocutory. There may be paraphasic errors with incorrect word substitutions.

In advanced disease, impaired comprehension and word finding difficulties are more pronounced. The ability to communicate effectively becomes impaired. The patient’s speech may become nonfluent with mainly short simple phrases or words. Echolalia and palilalia may also occur as affected individuals develop complete loss of verbal expression. These deficits may extend to reading and writing ability. Some affected individuals may retain their ability to understand and respond to non-verbal and emotional cues.

Visuo-spatial Function

Visuo-spatial cognitive impairment and non-verbal visuo-spatial information processing are the characteristic visuo-spatial disturbances observed in Alzheimer’s disease. Visual discrimination, visual recognition and visuo-spatial attention deficits may also occur, but less frequently. Although subtle impairments may be seen with early Alzheimer’s disease, deficits occur more commonly in moderate to severe stages of dementia and often become progressive. There may be impairment in ability to synthesize, integrate and organize visual sensory stimuli or other environmental information. There may also be difficulty developing strategies for complex construction. Some persons with Alzheimer’s disease have impaired right-left orientation and defective re-visualization, which involves internally re-visualizing and imagining a named object and then describing it accurately when prompted. Some may have difficulty with the synthesis of parts of an object into a whole and then properly identifying the whole (classic agnosia). Patients may also have difficulty copying or drawing objects and, with further progression of the illness, lose the ability to construct complex figures or diagrams. Rarely patients present with reduplicative paramnesia, involving the belief that they are in two or more locations simultaneously. Reduplicative paramnesia, more often seen following head injury, can also be regarded as a misidentification syndrome.

Praxis

Impairments with planned motor movements are closely related to executive dysfunction. These deficits are usually seen in advanced stages of Alzheimer’s disease dementia. Ideomotor and ideational apraxias may occur earlier. Ideomotor apraxia is characterized by inability to execute learned movements when prompted despite intact comprehension, sensation, motor strength and coordination. There may be difficulty in organizing and sequencing of movements involved in executing an action, e.g. pantomiming combing one’s hair or brushing teeth. Individuals with Alzheimer’s disease may exhibit motor perseveration and poor limb positioning. Ideational apraxia is the inability to perform an action comprised of several steps. An example is pantomiming the act of getting dressed or changing the batteries in a remote control. Given the profound limitations to daily function from apraxia, these symptoms can be very distressing to both patients and care providers. There may also be difficulty recalling the ability to perform previously learned tasks such as driving, using utensils, toileting and self-care.

Executive Dysfunction

Impairment of executive function may result in cognitive, mood, behavioural and personality changes. The latter are discussed later as part of NPS. The cognitive symptoms of executive dysfunction are closely related to higher intellectual capacity and involve several aspects of higher intellectual function, including planning, sequencing, abstraction, set shifting and organizing. Features of executive dysfunction arise commonly early in the course of Alzheimer’s disease, and may be the primary reason why functioning becomes impaired and care is sought. There is often loss of generative thought, and inability to plan or organize several mental tasks simultaneously without the use of aids. Individuals who previously did not require daily to-do lists to successfully perform tasks may have progressive difficulty completing activities.

It is important to note that there are age-associated declines in executive function; however, the mental flexibility that allows for the adaptive skills in the absence of dementia is often absent with Alzheimer’s disease. Ability to solve problems mentally is affected early. In addition, there may be impairment in symbolic and abstract thinking. Thoughts become more concrete and patients may have difficulty accurately interpreting proverbs. Poor response inhibition (e.g. impaired Stroop colour-word interference test), reduced ability to sustain and divide attention, and perseveration of sequential motor tasks can also be seen in Alzheimer’s disease at any stage of dementia or in the clinical prodrome to dementia.

NON-COGNITIVE NEUROPSYCHIATRIC SYMPTOMS ASSOCIATED WITH ALZHEIMER’S DISEASE

Neuropsychiatric symptoms such as depression, apathy, agitation and delusions are nearly universal in dementia associated with Alzheimer’s disease. Over time, over 98% of individuals with Alzheimer’s disease experience at least one NPS disturbance during the course of their illness⁷. In Alzheimer’s disease, the presentation, severity and frequency of these symptoms may fluctuate with progression of the illness. NPS can be classified based on individual symptoms or clusters of frequently co-occurring symptoms⁸. The Neuropsychiatric Inventory (NPI) helps distinguish neuropsychiatric symptoms and signs into 12 domains: delusions, hallucinations, agitation, dysphoria, anxiety, apathy, irritability, euphoria, disinhibition, aberrant motor behaviour, night-time behaviour disturbances, and appetite and eating abnormalities⁹ (Table 41.2).

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