Clinical manifestations and diagnosis of Alzheimer disease

INTRODUCTION - Alzheimer disease (AD) is a neurodegenerative disarray of indefinite cause and pathogenesis that mainly affects older adults. The fundamental clinical manifestations of AD are selective retentiveness impairment and dementia. AD is the most frequent cause of dementia. While treatments are available that can modulate the course of the disease and/or amend many symptoms, there is no cure, and the disease inevitably progresses in all patients.

This topic recaps the clinical manifestations and diagnosis of AD. Other topics review the risk components and treatment of AD and the clinical manifestations of other causes of dementia and cognitive impairment.

DEMOGRAPHIC FEATURES - Alzheimer disease (AD) is characteristically a disease of elderly years. It is rare for AD to occur before age 60. The incidence and prevalence of AD increase exponentially with age.

AD is slightly more common in women than men, with a comparative risk of 1.5. This does not seem to be explicated by the larger longevity in women.

There are hereditary classes of AD, all autosomal dominant, that routinely present before age 65, and frequently in the fifth decade or earlier. These account for less than 5 percent of all cases of AD. Patients with Down syndrome acquire AD at an earlier age, 10 to 20 years younger than the standard population with AD.

Other risk classes for AD are discussed separately.

CLINICAL FEATURES

Retentiveness impairment - Memory impairment is an essential feature of AD and is often its earliest expression. Even when not the fundamental complaint, memory shortfalls can be aroused in most patients with AD at the time of demonstration.

The design of memory impairment in AD is also peculiar. Declarative memory for facts and events, which reckon on mesial temporal and neocortical structures are profoundly impacted in AD, while subcortical systems supporting procedural memory and motor learning are relatively spared until rather late in the disease. A subset of declarative memory, that of specific events and contexts (episodic memory) is more profoundly impaired in early AD, compared with retention for facts such as vocabulary and constructs (semantic memory), which frequently becomes impaired somewhat later. Semantic memory is encoded in neocortical (nonmesial) temporal regions.

Within episodic memory, there is a differentiation between instant recall (eg, mental rehearsal of a telephone number), memory for recent events (which comes into play once material that has departed from consciousness must be recalled), and memory of more removed events. Memory for recent events, processed by the hippocampus, entorhinal cortex, and associated structures in the mesial temporal lobe, is conspicuously impaired in early AD. In contrast, immediate memory (encoded in the sensory association and prefrontal cortices) is spared early on, as are memories that are integrated for prolonged periods of time (years), which can be remembered without hippocampal function.

The early retention deficit in AD is most exactly identified as anterograde long-term episodic amnesia. Because the absolute time interval over which long-term memory can give way can actually be short (eg, inability to remember a few words after a couple minutes of distraction), patients and caregivers typically refer to "short-term memory" problems. For this reason, we attempt to avoid the confusion yielded by the technical terms of long-term and short-term memory and use the term "recent memory impairment" to refer to the characteristic damage.

Memory deficits build up insidiously and build up slowly over time, evolving to include deficits of semantic memory and immediate recall. Deteriorations of procedural memory appear only in late phases of AD.

Memory is normally tested by asking patients to remember three objects instantly and then at a delay of 5 to 10 minutes. Questions about orientation and recent current events are also useful memory tests. Clinicians should not rely on a patient's report of memory impairment, as many older people are errant reporters of their own retention impairment and can both over and under estimate their deficits.

Amnestic mild cognitive impairment - A state of restricted anterograde long-term retentiveness impairment, with preserved general cognitive, interpersonal functioning is identified as amnestic mild cognitive impairment (MCI). Amnestic MCI is more and more known as an early level of AD, with a transition rate to dementia at about 10 to 15 percent per year.

Other aspects of cognitive decline - Deficits in other cognitive fields may appear with or after the development of memory impairment. Speech function and visuospatial skills tend to be struck comparatively early, while deficits in executive function and behavioural symptoms oftentimes manifest afterward in the disease course. These deficits appear and build insidiously.

Language - Verbal dysfluency and anomia are frequently early characteristics of AD and are sometimes the exhibiting feature. The initial manifestations of speech disfunction normally include word-finding troubles, circumlocution, and diminished vocabulary in instinctive language and with anomia on confrontational naming tests. This advances to include agrammatism, paraphasic mistakes, poor speech content, and impaired comprehension. Patients can usually repeat phrases word for word until the disease is quite advanced.

Language dysfunction and loss of semantic retention are interconnected in AD. Some researchers have determined that loss of semantic fluency is an early finding in AD. When asked to give word lists in one minute's time, patients with AD perform significantly worse on a category fluency test (eg, lists of animals) than on a letter fluency test (eg, lists of words starting with F). Typical execution is age associated, with at least 15 items anticipated at age 65.

Visuospatial skills - Loss of visuospatial skills is an early characteristic of AD that is sometimes very conspicuous at presentation. Visuospatial impairments manifest as malposition of details and difficulty navigating in first unknown then familiar terrain. Ocular agnosia (inability to recognize objects) and prosopagnosia (inability to recognize faces) are later characteristics. Some clinicians have identified hemispatial visual neglect in their patients with AD.

Visuospatial skills may be tested by asking patients to re-create simple images (eg, intersecting pentagons) and to make a clock face. The latter, when merged with a request to fill in the time at "ten after eleven," is a deceptively problematical test and evaluates semantic knowledge as well as executive and spatial performance.

Insight - Reduced perceptiveness into his or her deficits (anosognosia) is a typical feature of AD and has been linked to frontal lobe pathology. It is common for patients to undervalue their deficits and offer excuses or explanations for them when they are pointed out. Questioning a collateral historian, normally a family member, who has known the patient over time, is facilitative, and often it is the family member, not the patient, who takes the complaint of cognitive deterioration to medical attention.

Loss of insight increments over time along with widespread disease severity. Proportional loss of insight is linked with behavioral disturbances; those with comparatively preserved insight are more apt to be depressed, while those with more impaired insight are likely to be agitated, disinhibited, and present psychotic characteristics.

Apraxia - Dyspraxia, or difficulty executing learned motor tasks, commonly comes about later in the disease after deficits in retentiveness and speech are apparent. Before it is clinically apparent, dyspraxia can be aroused by asking the patient to perform ideomotor tasks, ie, pantomime the use of tools (eg, "show me how you would use a comb"). Clinical dyspraxia leads to increasing difficulty first with complicated, multi-step motor activities, then with getting dressed, eating, and other self-care tasks and is a big contributor to dependency in middle to late degrees of AD.

Executive function - In early stages of AD, deterioration in executive function may be subtle rather than direct; family members and coworkers may find them less motivated and interested. In addition to poor insight, diminished ability for abstract thinking may be aroused. As the disease builds, a more obvious modification of personality, poor judgment and planning, and an unfitness to finish projects typically emerges.

Neuropsychiatric symptoms - Neuropsychiatric symptoms are common in AD, particularly in the intermediate and late path of disease. These can start with subtle personality modifications including apathy, social disengagement, and disinhibition. The former may be a demonstration of superimposed depression, which can be difficult to diagnose in the context of dementedness.

More troublesome in patient management is the emergence of behavioral disruptions, including unrest, hostility, wandering, and psychosis (hallucinations, illusions, misidentification syndromes). A subsequent medical illness, medication toxicity, and other causes of delirium should be considered whenever new behavioral disturbances arise. The behavioral disturbances associated with AD are discussed in detail on an individual basis.