Major Neurocognitive Disorder of the Alzheimer’s type – Alzheimer’s Dementia

Alzheimer’s dementia refers to four main syndromes that have historically been associated with a common brain pathology called Alzheimer’s disease, highlighting the distinction between Alzheimer’s dementia (i.e., the symptoms of a person that we see on the surface) and Alzheimer’s disease (i.e., what’s going on
 

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underneath in their brain), requiring clarification of the abbreviation “AD.” The common underlying pathology of the four syndromes, Alzheimer’s disease, was originally defined by observations in the early 20th century that certain proteins we all have in our brains, called beta-amyloid and tau, cluster in abnormal ways in certain brain areas and interfere with normal brain function. Depending on the distribution of these proteins, especially tau, people develop different syndromic phenotypes. As we come to understand neurodegeneration better, it is becoming clearer that the so-called proteinopathy component of Alzheimer’s disease and other neurodegenerative diseases is only part of the whole picture, and instead several processes, such as immune, vascular, metabolic, and genetic, contribute at various degrees to the gradual functional and structural changes we see in people’s brains that give rise to symptoms.

• Late Age of Onset Alzheimer’s Dementia (LOAD) – Amnestic predominant: This is the most common presentation of Alzheimer’s dementia for the majority of people, affecting primarily people over the age of 65, and with the earliest and predominant symptom being difficulty with memory. It is not uncommon that caregivers will report that their loved ones forget appointments or conversations they recently had, despite being able to recall remote events in detail. Although the majority of people have Alzheimer’s disease in areas of the brain involved in memory consolidation, called the hippocampi, we are becoming aware that, more often than not, people tend to have more than one underlying brain pathology, much like people who have hypertension are more likely to also have high cholesterol or diabetes. As such, a significant number of people also have vascular brain disease or other neurodegenerative diseases under the microscope. This variability of what happens in people’s brains is characteristic in those presenting with Alzheimer’s dementia above the age of 80 where LATE, for Limbic-predominant Age-related TDP-43 Encephalopathy, can be the predominant brain pathology instead of Alzheimer’s disease. The above highlight the need of expert multidisciplinary approaches in caring for patients with dementia.
• Posterior Cortical Atrophy (PCA) – Visuospatial predominant: First described by D. Frank Benson, MD, PCA is less common than LOAD and presents in people of a somewhat younger age. Its unique features involve difficulty in visually recognizing complex shapes, such as a face, or exact distances or movement, such as a moving car, despite people having intact elementary visual abilities, such as being able to perceive colors or static shapes. This is because the brain is unable to synchronize its function and combine individual elements of an image into a gestalt percept. PCA takes its name from the fact that areas responsible for these visual functions are in the posterior part of the brain. Many people delay being diagnosed because they assume their problems are caused by poor eyesight, and because other cognitive abilities, such as memory, are intact. Even more, they often suffer from depression that is incorrectly attributed to social rather than brain causes. The underlying pathology of PCA is almost exclusively Alzheimer’s disease.
• Logopenic Primary Progressive Aphasia (lvPPA) – Language predominant: The term Primary Progressive Aphasia (PPA) refers to three syndromes where people’s first and predominant difficulties involve a gradually progressive deficit in language, and they are further subdivided into three subtypes: logopenic, non-fluent/agrammatic, and semantic. The first is one of the Alzheimer’s dementia syndromes, whereas the latter two fall under Frontotemporal Dementia Syndromes. People with lvPPA have a predominant language deficit of word-finding difficulties, which is the result of left posterior temporal lobe dysfunction. People present with marked pauses between words when speaking because they search for the right word, even though they know what words mean, and often use a roundabout way in expressing themselves. It is also common they retain less information when spoken to because it is difficult for them to grasp at once long sentences. This explains why being spoken to with short and direct sentences is a more effective way of communicating with them. For a subset of patients with lvPPA, a history of dyslexia is common, whereas the underlying pathology is almost exclusively Alzheimer’s disease.
• Early Age of Onset Alzheimer’s Dementia (EOAD) – Dysexecutive-Behavioral predominant: A less common phenotype of Alzheimer’s dementia is EOAD, where symptoms start at an age younger than 65 years old. In contrast to its counterpart, LOAD, memory difficulties may not be the predominant deficit, and instead difficulty in organizing and planning (key features of executive function), or marked apathy, are often driving daily difficulties. Furthermore, and in contrast to the other three Alzheimer’s dementia syndromes, brain atrophy is less pronounced, often requiring specific biomarkers of neurodegeneration to verify the diagnosis.