Alzheimer’s Dementia

Synonyms

Alzheimer’s disease; Early-onset Alzheimer’s disease; Familial Alzheimer’s disease; Late-onset Alzheimer’s disease; Senile dementia of the Alzheimer’s type

Short Description or Definition

One of the leading causes of dementia in late life, Alzheimer’s dementia (AD) is a progressive neurodegenerative disorder characterized by a gradual onset and progressive course, affecting memory and other cognitive domains. Traditionally, a diagnosis of AD is made if the cognitive impairments do not occur exclusively in the context of other conditions that affect cognitive status (e.g., delirium, depression, medication side effects, thyroid malfunction, or certain vitamin deficiencies) and are of sufficient severity to cause impairment in social or occupational functioning. Recent changes to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-V), allow a diagnosis of AD under either major or mild neurocognitive disorder. The criteria for major neurocognitive disorder state that cognitive decline must be significant and interfere with daily activities (e.g., paying bills, managing household chores, or shopping), whereas mild neurocognitive disorder represents “modest” decline that does not necessarily interfere with accomplishing daily tasks. A diagnosis of mild neurocognitive disorder due to Alzheimer’s disease can be made if the condition has not yet progressed to interfere with daily functioning (American Psychiatric Association 2013). Diagnoses of AD are based on the history and presentation of clinical symptoms, evidence of cognitive impairment, and the exclusion of other causes of dementia such as stroke, metabolic disorders, or other conditions that may account for the cognitive impairment. A diagnosis of definite AD is based upon postmortem neuropathological analysis and is made when there are sufficient numbers of senile plaques and neurofibrillary tangles in specific brain regions.

Categorization

AD may be categorized according to onset age, family history, or presenting clinical features. Age categories distinguish between early (occurring before age 65) and late (occurring at age 65 and older) onset. Classifications based on family history (familial AD vs. sporadic AD) distinguish AD forms that show high heritability. Familial AD is rare, generally of early onset, and has been associated with mutations in the APP gene on chromosome 21, presenilin 1 gene on chromosome 14, and presenilin 2 gene on chromosome 1 (Hardy 2003). Its transmission resembles an autosomal dominant pattern (Morris and Nagy 2004).

AD has also been classified according to the clinical presentation of symptoms. Its most common presentation involves early and significant memory impairment. Variants to this presentation have been reported in the literature and include a visual (posterior) form with significant impairment in higher-level processing of visual stimuli, an aphasic form with significant language involvement, and a frontal form with prominent impairment of executive functions. At autopsy, these variants usually exhibit AD neuropathology in brain regions typically involved in the specific neuropsychological domain (Grabowski and Damasio 2004).

Epidemiology

AD is the most common cause of dementia in late life, accounting for 60–80% of all cases (“2015 Alzheimer’s” 2015). Current estimates suggest 5.3 million individuals suffer from AD in the United States, and projections based on population trends suggest an increase to 13.8 million by 2050, including approximately seven million individuals aged 85 and older (Hebert et al. 2013). The overall prevalence of AD is about 11% in individuals age 65 years or older in America and increases with age to include 32% of persons aged 85 and older (Hebert et al. 2013). Incidence rates also exhibit an age-related increase. For example, of the 473,000 individuals that are projected to develop AD in 2015, just 61,000 new cases represent those aged 65 to 74, while 172,000 new cases are among those age 75 to 84, and the final 240,000 cases are among individuals aged 85 and older (the “oldest-old”) (“2015 Alzheimer’s” 2015; Hebert et al. 2013). Studies report differing patterns of AD prevalence and incidence at the upper end of the life span, with some reporting a plateau at very old ages (age 90 or 100; Mendez and Cummings 2003). Additionally, research demonstrates racial differences in the prevalence of dementia with higher rates among Black and Latino populations. Some of these differences are attributed to differences in cardiovascular risk (“2015 Alzheimer’s” 2015).

Risk Factors

Increasing age is among the strongest risk factor for AD. Other risk factors include the e4 allele of the apolipoprotein E (APOE) gene, positive family history (also in sporadic AD), low education (possibly due to less neural reserve), female sex (even after accounting for differential survival), history of head trauma, and cardiovascular factors (“2015 Alzheimer’s” 2015; Tschanz et al. 2013). Well-established vascular risk factors include hypertension, high cholesterol, and diabetes (Tschanz et al. 2013). Some of these risk factors affect AD risk when occurring earlier in the life span. For example, studies suggest that high blood pressure, high serum cholesterol, and obesity in midlife increase the risk of AD later in life (“2015 Alzheimer’s” 2015; Kivipelto et al. 2005). Although inconsistent, some studies report treatment with antihypertensive medications or cholesterol-lowering agents reduces risk for AD (Soininen et al. 2003). Among potential “protective” factors, data from epidemiological studies suggest a lower risk of AD among women receiving hormone replacement therapy (Zandi et al. 2002b; Kawas et al. 1997). However, a large randomized clinical trial of estrogen and estrogen+progesterone in elderly women suggested an increase in all-cause dementia in those receiving the combination hormone treatment. Thus hormone therapy is not recommended for cognitive health (Malaspina et al. 2008). Other modifiable risk factors that have shown potential benefits for cognitive health and reduced risk for dementia include diet, nutrients, and nutrient supplements such as antioxidant vitamins, omega-3 fatty acid, medications such as nonsteroidal anti-inflammatory agents, and lifestyle practices such as physical activity and cognitive and social engagement (Scarmeas et al. 2009; Zandi et al. 2002a; Wengreen et al. 2009; Morris 2012; Engelhart et al. 2002; Norton et al. 2012; Wang et al. 2012).

Natural History, Prognostic Factors, Outcomes

The clinical course of AD is usually one of the gradual onset of symptoms with progressive decline. Many scientists believe the disease process starts in the brain decades before overt symptoms emerge. A preclinical phase, characterized primarily by episodic memory deficits, heralds the onset of symptoms. This stage, also referred to as mild cognitive impairment (MCI), lasts approximately 1–3 years. Progression to dementia is characterized by increasing severity of cognitive impairment with severe memory deficits, visuospatial impairment, and other perceptual disturbances. Language impairment begins with mild naming difficulties and circumlocutory speech but progresses to include comprehension deficits. Apraxia (difficulty performing learned motor tasks in the absence of impairment in primary motor or sensory functions) and impaired executive functions and computational ability are also apparent. Behavioral changes are common with indifference, irritability, and sadness, progressing to delusions and, in some individuals, more severe psychiatric disturbances such as hallucinations and agitation. In end stages, there is severe deterioration of all cognitive functions, speech is generally unintelligible, and motor rigidity and urinary and fecal incontinence are present. Death may occur as the result of other causes such as pneumonia or infections (Mendez and Cummings 2003). On postmortem exam, the brain is characterized by generalized atrophy and sulcal and ventricular enlargement. Figure 1a and b display gross atrophy of an AD brain compared with a brain from a cognitively normal elderly individual. Figure 2 displays a coronal section of an AD brain at the level of the hippocampus.

Alzheimer’s Dementia, Fig. 1

(a and b) Displays the brains from a cognitively normal elderly individual and an individual who suffered from advanced AD, respectively. Note the severe atrophy apparent in the AD brain (Photo courtesy of Christine Hulette, M.D., Bryan Alzheimer Disease Research Center, Duke University. Used by permission of Elsevier Limited)

Alzheimer’s Dementia, Fig. 2

Displays atrophy in AD in this coronal section including the hippocampi. Note dilated lateral ventricles and loss of inferior temporal mass are present bilaterally (Photo courtesy of Steven S. Chin, M.D., Ph.D., University of Utah Health Sciences Center)

The duration of the entire disease course from MCI to death is highly variable. Mean survival estimates from symptom onset range from 4 to 8 years, but some studies have reported considerably longer duration of 20 years (“2015 Alzheimer’s” 2015). Regardless of duration, one study suggests that individuals will spend the majority of their total years with AD in the most severe stage (Arrighi et al. 2010). More rapid rate of disease progression has been associated with early, prominent language impairment, frontal features, and extrapyramidal signs (Mendez and Cummings 2003). Studies examining risk factors of progression after AD onset indicate more rapid decline of cognitive and functional deficits for females, those with earlier onset ages, and those with comorbid vascular risk factors. Alternatively, use of various vascular treatments and cholinesterase inhibitors has been associated with slower rates of decline (Tschanz et al. 2013).

Neuropsychology and Psychology of Alzheimer’s Dementia

Neuropsychological Deficits

The neuropsychology of AD follows the clinical progression. In early stages, memory is almost always involved, with specific deficit in learning new information. Remote memory such as memory for autobiographical or other knowledge-based systems (semantic memory) is relatively unaffected. In early stages, standardized testing with word lists may reveal relative preservation of immediate or working memory but impairment in delayed (free) recall. There is usually some benefit from cuing or recognition procedures. With progression, cuing is no longer helpful, and remote recall is affected. Implicit memory may be relatively spared as patients show evidence of learning on priming or procedural motor tasks. Orientation to time and place is also affected in AD (Knopman and Selnes 2003).

Language impairments progress from mild anomia and word finding difficulties in early stages to include impairment in comprehension and writing. Errors in speech (paraphasias) become more common, and word substitutions become progressively less related to the target words. Repetition of speech may be relatively unaffected until late in the disease course (Mendez and Cummings 2003; Knopman and Selnes 2003). Sensitive to changes in language are tests of verbal fluency and confrontation naming. Visuospatial disturbances may be subtle or nonexistent in the earliest stages of AD. In moderate and severe stages, impairment may be evident on figure copying tasks or judgment of line orientation (Knopman and Selnes 2003). Figure 3 displays characteristic examples of visuoconstructional impairment in four representative patients with AD.

Alzheimer’s Dementia, Fig. 3

Displays visuoconstructional impairments in the drawings of four individuals with possible or probable AD. The stimulus is the left-most figure (Photographs courtesy of Norman L. Foster, M.D., and Angela Y. Wang, Ph.D., Center for Alzheimer’s Care, Imaging and Research, University of Utah)

Impaired abstract reasoning, sustained attention, planning, judgment, and problem-solving may characterize impairment in executive functions. Deficits in executive functions may be demonstrated on tests of verbal fluency, trailmaking, and set shifting. Tests such as the Rey complex figure and clock drawing may also elicit impairment in executive functions with poor planning and execution of the tasks. Deficits in working memory may be evident on tasks requiring mental manipulation or divided attention (Knopman and Selnes 2003).

Other neurocognitive aspects of AD include apraxia and anosognosia. In mild AD, deficits in praxis are not common but emerge later in the disease course. Assessment of apraxia may involve pantomiming the execution of a task. Anosognosia or an unawareness of disability is extremely common (Knopman and Selnes 2003). Standardized assessment approaches are few. Some approaches rely on clinical observation, noting a discrepancy between self-report of cognitive impairment and test performance or a discrepancy between caregiver and patient report of impairment.

Behavioral Symptoms

Behavioral changes are extremely common in AD, with nearly all individuals exhibiting at least one symptom at some point over the disease course. Among the most common of these changes is apathy, characterized by a lack of interest and indifference. Anxiety, irritability, and depression are also common, as are delusions. Some patients may exhibit hallucinations, and particularly challenging for caregivers and family are disruptive behaviors such as agitation and aggression. The course of behavioral symptoms is variable, with severe episodes alternating with milder ones, raising questions about environmental triggers. Noting the co-occurrence of several behaviors, some scientists believe these symptoms are better conceptualized as behavioral syndromes, with implications for underlying brain pathology. Several questionnaires are available for assessing behavioral symptoms, ranging from a single symptom questionnaire to a large inventory of symptoms. Assessment of behavioral symptoms is particularly important in an AD evaluation as their presence may suggest other causes for dementia.

Evaluation

A thorough dementia work-up is important for diagnosing AD or determining the etiology of dementia. Critical elements of an evaluation include a detailed clinical history, mental status and physical exam, and, due to potential inaccuracies in patient reporting, an interview with a reliable informant. Neuropsychological testing, laboratory, and neuroimaging are important to exclude other causes of dementia.

Neuropsychological testing is especially important in determining severity of cognitive decline and developing a differential diagnosis between dementia and cognitive deficits due to other conditions. Neuropsychologists may administer a battery of standardized assessments of memory, visuospatial functioning, language, and executive functions and estimate a discrepancy between current and premorbid functioning based on normative data associated with those tests. Alternatively, many neuropsychologists may administer several follow-up examinations to identify patterns of cognitive change over time in establishing a diagnosis. Psychometric properties of these assessments as well as reliable change methods should be considered when determining the validity and reliability of results. While practice effects are generally considered problematic, recent research has elucidated the utility of practice effects for prognosis and differential diagnosis (Chelune and Duff 2013).

Laboratory testing may include a blood count, routine chemistries, thyroid function, and B12 levels. Neuroimaging with MRI or CT may reveal generalized cerebral atrophy with associated sulcal widening and ventricular enlargement. In early stages of the disorder, the brain may appear normal on MRI/CT. PET imaging is a more sensitive technique for detecting changes in brain function in early stages. Reduced glucose metabolism, usually in the temporoparietal regions, is a consistent pattern in early AD. Figures 4, 5, and 6 display the pattern of glucose hypometabolism in MCI and AD compared with a cognitively normal elderly individual. Additional examination of biomarkers, such as sampling cerebrospinal fluid for tau and amyloid-B42 assays, may be helpful as supplemental procedures for complex cases (Mendez and Cummings 2003).

Alzheimer’s Dementia, Fig. 4

These images are processed FDG-PET images obtained from elderly subjects. The images have been processed using Neurostat stereotactic surface projections to illustrate the changes of the brain in Alzheimer’s disease. Subject scans are shown in two rows in each figure, depicting projections onto six surfaces: R-lateral, L-lateral, R-medial, L-medial, superior, and inferior. The top row in each figure displays regional glucose metabolism with “cooler” colors (purple, blue) reflecting areas of hypometabolism. The bottom row in each figure displays relative glucose metabolism for each participant as compared with a normative sample of 27 cognitively normal elderly individuals. In this bottom series, the images display the statistical significance, expressed as Z-scores, of the hypometabolism when compared to those of the normative sample. The brighter colors (red, white) represent areas of significant hypometabolism, and the cooler colors of blues and purples represent relatively normal brain metabolism. 74-year-old control subject with normal cognition. The top row shows normal brain metabolic activity, and the lower row shows very few regions of hypometabolism. The areas of significant hypometabolism indicated in the medial views are due to this individual having enlarged lateral ventricles relative to normative subjects (Photographs courtesy of Norman L. Foster, M.D., and Angela Y. Wang, Ph.D., Center for Alzheimer’s Care, Imaging and Research, University of Utah)

Alzheimer’s Dementia, Fig. 5

These images are processed FDG-PET images obtained from elderly subjects. The images have been processed using Neurostat stereotactic surface projections to illustrate the changes of the brain in Alzheimer’s disease. Subject scans are shown in two rows in each figure, depicting projections onto six surfaces: R-lateral, L-lateral, R-medial, L-medial, superior, and inferior. The top row in each figure displays regional glucose metabolism with “cooler” colors (purple, blue) reflecting areas of hypometabolism. The bottom row in each figure displays relative glucose metabolism for each participant as compared with a normative sample of 27 cognitively normal elderly individuals. In this bottom series, the images display the statistical significance, expressed as Z-scores, of the hypometabolism when compared to those of the normative sample. The brighter colors (red, white) represent areas of significant hypometabolism, and the cooler colors of blues and purples represent relatively normal brain metabolism. 60-year-old subject clinically diagnosed with MCI. The top row shows symmetric decreases in metabolic activity in both hemispheres of the brain. Abnormalities are primarily in the parietal lobe (shown in the R-lateral and L-lateral views) and the posterior cingulate cortex (shown in the R-medial and L-medial views), as seen in the green regions. The bottom row confirms that these regions (green, yellow, and red areas) are indeed significantly (Z-scores > = 2.5) hypometabolic. This pattern is a distinguishing feature of AD seen in FDG-PET studies (Photographs courtesy of Norman L. Foster, M.D., and Angela Y. Wang, Ph.D., Center for Alzheimer’s Care, Imaging and Research, University of Utah)

Alzheimer’s Dementia, Fig. 6

These images are processed FDG-PET images obtained from elderly subjects. The images have been processed using Neurostat stereotactic surface projections to illustrate the changes of the brain in Alzheimer’s disease. Subject scans are shown in two rows in each figure, depicting projections onto six surfaces: R-lateral, L-lateral, R-medial, L-medial, superior, and inferior. The top row in each figure displays regional glucose metabolism with “cooler” colors (purple, blue) reflecting areas of hypometabolism. The bottom row in each figure displays relative glucose metabolism for each participant as compared with a normative sample of 27 cognitively normal elderly individuals. In this bottom series, the images display the statistical significance, expressed as Z-scores, of the hypometabolism when compared to those of the normative sample. The brighter colors (red, white) represent areas of significant hypometabolism, and the cooler colors of blues and purples represent relatively normal brain metabolism. 72-year-old subject clinically diagnosed with AD. This subject shows an even greater and more widely distributed decrease in glucose metabolism. Parietal and temporal lobes and posterior cingulate cortex (green and blue regions in the top row) are affected. The statistically significant changes in metabolic pattern (red and white regions in the lower row) are much greater than the MCI case (Photographs courtesy of Norman L. Foster, M.D., and Angela Y. Wang, Ph.D., Center for Alzheimer’s Care, Imaging and Research, University of Utah)

All acquired data are used in differential diagnosis under the DSM-V and National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer’s Disease and Related Disorders Association (NINCDS-ADRDA) criteria (American Psychiatric Association 2013; McKhann et al. 1984). In 2011 the National Institute on Aging (NIA) and Alzheimer’s Association workgroup proposed updated criteria to increase diagnostic range and specificity, including a preclinical stage of AD before symptom onset and incorporation of diagnostic biomarkers (McKhann et al. 2011). These criteria are gaining supporting scientific evidence toward their validity although further evaluation is required before they are adopted in clinical settings (“2015 Alzheimer’s” 2015).

Treatment

Treatment for AD is palliative, with medications and therapies for symptom management. Medications most commonly used are cholinesterase inhibitors that functionally address the cholinergic deficit of AD by blocking the activity of the acetylcholine-degrading enzyme, acetylcholinesterase (see “Cholinesterase Inhibitors”). These medications are modestly effective, and patients and family may note an improvement in some cognitive and behavioral symptoms. However, the medications do not modify the trajectory of disease progression. In general, cholinesterase inhibitors are well-tolerated. The use of the first FDA-approved drug of this class, tacrine, however, is rarely administered now due to risk of liver toxicity. Other medications include donepezil, rivastigmine, and galantamine. Side effects include gastrointestinal symptoms such as diarrhea, nausea, and vomiting (Orgogozo 2003). Memantine, an NMDA glutamate receptor blocker, has been approved for use in moderate and severe AD with the mechanism of action presumably reducing neuronal excitotoxicity. Additionally, a sixth drug combining donepezil and memantine was approved in 2014 for use in moderate and severe AD (“2015 Alzheimer’s” 2015). Other treatments include the use of psychotropic medications (such as antidepressant and antipsychotic medications) to address the behavioral symptoms. Cognitive rehabilitation may be attempted early in the disease course while patients are still able to participate, and personalized psychosocial interventions such as reminiscence therapy and music therapy have gathered support (Cotelli et al. 2012). Furthermore, psychoeducation, behavioral techniques, and caregiver support and interventions are also important elements of clinical care.

See Also

• Cholinesterase Inhibitors

• Neurofibrillary Tangles

• Senile Dementia

• Senile Plaques