Derek Burnett
Derek Burnett is a Contributing Writer at Bottom Line Personal, where he writes frequently on health and wellness. He is also a contributing editor with Reader’s Digest magazine.
People often use the terms “Alzheimer’s disease” and “dementia” interchangeably, as if they were the same thing. In fact, Alzheimer’s is just one form of dementia. To put it another way, all Alzheimer’s is dementia, but not all dementia is Alzheimer’s. Just as diabetes has types 1 and 2, so does dementia have varying types, of which Alzheimer’s is one. Although all types of dementia are marked by a basic similarity in symptoms—cognitive decline—they vary in terms of causes, physiology, progression, and specific symptoms. People conflate Alzheimer’s with the umbrella term “dementia” because it’s the best-known and most often talked-about form of dementia. This is because it’s the most common form.
To better understand Alzheimer’s versus dementia, let’s look carefully at each of them, starting with dementia.
The National Institute on Aging (NIA) defines dementia as “the loss of cognitive functioning—thinking, remembering, and reasoning—to such an extent that it interferes with a person’s daily life and activities.” Dementia is often driven by disease, and whatever its type, the loss of cognitive functioning is rooted in damage to nerve cells (neurons) in the brain or to the connections between those nerve cells, or to both. When neurons die or lose their ability to transmit information from one to another, the person experiences cognitive lapses.
When most people think about dementia, they think immediately of memory loss. But as the NIA’s definition makes clear, dementia isn’t just about forgetting. It’s also about the debilitating loss of the ability to reason and to think clearly. As all of these aspects of cognition decline, the person becomes increasingly unable to take care of his or her daily needs, and eventually becomes completely dependent on others.
Alzheimer’s is one of five main types of dementia. The other four are frontotemporal dementia, vascular dementia, Lewy Body dementia, and mixed dementia. Dementia may also be caused by other illnesses such as Parkinson’s disease, or by treatable underlying conditions such as sleep disorders or medication side effects.
FRONTOTEMPORAL DEMENTIA (FTD) gets its name from the parts of the brain most affected, namely the frontal lobe and temporal lobe. Those are the areas of the brain most closely associated with reasoning, personality, language and behavior. FTD has two main types: one primarily affecting language, and the other behavior and personality. FTD differs from Alzheimer’s in that, typically, changes to language and personality are its earliest signs, whereas in Alzheimer’s the first symptoms tend to be deficits in short-term memory (people with FTD also will experience memory loss, but usually later in the disease process). FTD usually appears earlier in life than Alzheimer’s, with most cases occurring between ages 45 and 60.
VASCULAR DEMENTIA ALSO BEARS A DESCRIPTIVE NAME. “Vascular” refers to the blood vessels, and vascular dementia is cognitive loss when major blood vessels leading to the brain become damaged or obstructed, often by a stroke or a series of scarcely noticeable mini-strokes. The early signs of vascular dementia tend to be lapses in judgment and poor planning, organizing, and decision-making. Later, as with Alzheimer’s and frontotemporal dementia, the person will suffer severe memory loss.
LEWY BODY DEMENTIA (LBD), sometimes called dementia with Lewy bodies, is caused by a buildup in the brain of a protein called Lewy bodies. When these proteins accumulate in a part of the brain called the cerebral cortex, they have a devastating effect on visual processing, thinking, and attention. Besides having trouble staying alert and attentive, people with LBD begin having difficulty sleeping, and experience sometimes frightening visual hallucinations.
MIXED DEMENTIA is the term given to a person with more than one type of dementia. Because there is so much overlap in the symptoms of the different types of dementia, most such people are not diagnosed with mixed dementia, but rather the label is applied when their brains are studied post-mortem and doctors observe brain changes typical of more than one type of dementia.
Between 60% and 80% of all cases of dementia are Alzheimer’s disease. What sets Alzheimer’s apart from the other forms of dementia are two specific changes that occur in the brain…the formation of amyloid plaques and neurofibrillary tangles.
Amyloid-beta precursor is a protein that we all have in our brains, which helps us repair damage to nerve cells and grow new ones. In Alzheimer’s, regulation of the protein becomes disrupted, and a damaged form of it called beta-amyloid begins to build up and clump together into plaques. These beta-amyloid plaques may block communication between neurons in the gaps called synapses, and their presence may also trigger an inflammatory response that wipes out brain cells.
Neurofibrillary tangles are structures formed by another brain protein called tau. In a healthy brain, tau helps us maintain the strands within brain cells that deliver materials essential to proper cell function. But when a person has Alzheimer’s, the tau becomes twisted and those strands lose their integrity. When the cell loses its ability to transport nutrients and other essential supplies, it dies.
Indeed, the death of neurons is the third hallmark of Alzheimer’s disease, although it shares this third feature with other forms of dementia. As amyloid plaques, neurofibrillary tangles, and inflammation effect their damage on brain cells and the connections between them, so many neurons die and are cleared away that the brain literally begins to shrink in volume and the disease worsens as more and more parts of the brain are compromised.
That explanation sounds fairly straightforward, but recent attempts to reverse Alzheimer’s by clearing away amyloid have proven disappointing, suggesting that the disease is quite complex and may involve the interplay of several factors that are hard to pin down.
These processes are now thought to begin some 20 years before Alzheimer’s symptoms first appear. On average, those diagnosed live only four to eight years after being told they have the disease, although some may survive for up to two decades with it. Thankfully, we learn more and more about Alzheimer’s with every passing year. In years to come, researchers may develop ways to prevent, slow, or even reverse Alzheimer’s and other forms of dementia.
