What Is Dementia?

March 3rd, 2025

According to the National Institute on Aging, dementia is a term that describes a group of symptoms related to thinking, memory and changes in personality. The symptoms are chronic (long-lasting) and severe enough to interfere with the person’s day-to-day activities. Although they vary considerably from one individual to another, these symptoms commonly include the following: 

• Problems with memory, especially short-term memory
• Difficulty performing familiar tasks, such as preparing breakfast or getting dressed
• Language difficulties
• Changes in visual perception
• Disorientation
• Diminished judgment
• Difficulty concentrating
• Changes in mood or behavior

Typically, these changes come about gradually and slowly worsen over time. They may also wax and wane — a person with dementia may seem very lucid in one moment, and quite confused in the next. 

Types of Dementia

Dementia is not a disease in its own right. Rather, it is a symptom of an underlying problem in the brain. In fact, according to the Alzheimer’s Society of Ireland, there are at least 400 different types of dementia, although a few disease processes account for the bulk of cases seen. These include the following: 

Alzheimer’s Disease

Alzheimer’s disease is a progressive, irreversible brain disease that gradually destroys memory and thinking skills. Symptoms usually begin when a person is in their mid-60s, although a subtype of Alzheimer’s disease, known as early-onset Alzheimer’s, can occur in people who are younger than 65. Alzheimer’s disease is named for Dr. Alois Alzheimer, who discovered the condition in 1906. It is the most common cause of dementia and accounts for between 60% to 80% of cases in the U.S. 

Today, Alzheimer’s disease is thought to be caused by the accumulation of abnormal proteins in the brain. These proteins — beta amyloid and tau — form characteristic plaques and tangles that are believed to interfere with communication between nerve cells and prevent the absorption of essential nutrients within the cells. Research suggests that these abnormal proteins begin accumulating many years before symptoms of dementia begin. 

Additionally, a number of medical conditions and lifestyle factors  have been identified as risk factors for Alzheimer’s disease. These include:

• High blood pressure 
• Obesity
• Cardiovascular disease 
• Diabetes
• Physical inactivity
• Smoking
• Alcohol misuse

Stages of Alzheimer’s & Associated Symptoms

Alzheimer’s disease progresses slowly but inexorably in fairly typical stages. As of this writing, seven stages have been identified. Below is an overview of the symptoms associated with each:

• Stage One:
  • Begins 10-15 years before symptoms develop
  • No cognitive decline 
  • No complaints of memory problems
• Stage Two: Mild forgetfulness
  • Mild memory problems, such as misplacing items or forgetting names. 
  • Memory lapses may increase in frequency
  • Social and work life are unaffected.
• Stage Three: Noticeable problems with memory
  • Impaired concentration
  • Trouble remembering recently read books or magazines
  • Trouble organizing or remembering plans
  • Some difficulty with work or household tasks
• Stage Four: Significant memory loss and other cognitive skills
  • Difficulty remembering what day it is
  • Wandering or getting lost
  • Sleep problems; “sundowning” (waking at night and sleeping during the day)
  • Inappropriate clothing choices
• Stage Five: Significant cognitive impairment
  • Difficulty remembering people close to them
  • Trouble completing basic tasks such as bathing and dressing
  • Psychological symptoms such as hallucinations, paranoia or delusions
• Stage six: Severe symptoms
  • Unable to complete activities of daily living independently
  • Difficulty communicating: may not be able to come up with the right word for items  or activities
  • Emotional and behavioral difficulties including anger, aggression, paranoia, and delusions
• Stage seven: Loss of physical control
  • Lack of strength or ability to move independently
  • Swallowing difficulty
  • Incontinence
  • Greater susceptibility to infections

It’s important to note that these stages often overlap, and mild to moderate memory loss may last many years. 

Vascular Dementia

Vascular dementia is a form of dementia associated with cerebrovascular disease, which causes damage to the blood vessels in the brain. It is often associated with the same risk factors — high blood pressure, high cholesterol, atherosclerosis, Type II diabetes and cigarette smoking — that are known to increase the risk of Alzheimer’s disease, suggesting a link between the two. In fact, it is not uncommon for a person with vascular dementia to also have brain changes consistent with Alzheimer’s disease.

Symptoms of Vascular Dementia

The symptoms of vascular dementia are very similar to those of Alzheimer’s disease, and include the following:

• Problems with memory, thinking and organization
• Difficulty concentrating
• Confusion
• Changes in behavior and mood

Lewy Body Dementia

The third most common form of dementia, Lewy body dementia or LBD affects about 1 million people in the U.S. and is characterized by an abnormal accumulation of the protein alpha-synuclein in the brain. In healthy people, alpha-synuclein plays a role in helping nerve cells communicate with one another. But in LBD, this same protein forms clumps inside nerve cells that interfere with normal function and eventually cause the cells to die. These clumps also cause disruption of various brain chemicals, causing widespread damage to different parts of the brain. They are named Lewy bodies after the German neurologist Dr. Friederich Lewy, who discovered them in the brains of people with Parkinson’s disease in 1912. 

According to the National Institute on Aging, there are two forms of Lewy body dementia:

• Dementia with Lewy bodies, in which the cognitive changes characteristic of Lewy body dementia appear before the onset of movement problems.
• Parkinson’s disease dementia, in which cognitive symptoms develop after the onset of movement problems. According to the Alzheimer’s Association, between 50% and 80% percent of people with a diagnosis of Parkinson’s disease will experience dementia as the disease progresses. Research suggests that the time between a Parkinson’s diagnosis and dementia onset is about 10 years.  

Symptoms of Lewy Body Dementia

Unlike people with Alzheimer’s disease, who typically have memory problems early in the course of the illness, people with LBD tend to have few memory problems initially, and instead present with symptoms such as the following: 

• Trouble paying attention/loss of concentration
• Visual and spatial disturbances (for instance, not being able to judge distances correctly or not recognizing familiar objects) 
• Difficulty planning and multitasking
• Trouble problem solving 
• Visual hallucinations 
• Parkinsonism, a movement disorder characterized by stiff, slow movements, tremors, muscle rigidity, a flat facial expression, trouble speaking or swallowing, balance problems and falls

Sleep disorders, particularly insomnia and REM sleep behavior disorder, in which a person physically acts out troubling dreams by flailing, kicking, punching their bed partner and/or falling out of bed, are also common, and are often paired with excessive sleepiness during the day. 

Additionally, LBD causes dysregulation of the body’s autonomic nervous system, which controls automatic functions such as temperature regulation, perspiration, digestion and blood pressure. As a result, people with LBD may suffer physical symptoms such as the following:

• Sensitivity to heat and cold
• Dizziness and/or fainting
• Constipation
• Urinary incontinence
• Diminished sense of smell

Frontotemporal Dementia 

Frontotemporal dementia, or FTD, is a term used to describe a group of disorders that cause changes in personality, language and motor skills. Although relatively uncommon, it is a significant cause of dementia in people between the ages of 40 and 65. 

Frontotemporal dementia is the result of damage to one or two portions of the brain — the frontal and temporal lobes. Its symptoms differ from those of most other forms of dementia and reflect the functions that these two areas of the brain perform. 

Specifically, the frontal lobe, which is located just behind the forehead, is responsible for behavior, emotions, problem solving and planning, as well as speech. By contrast, the temporal lobes, located on either side of the brain, are responsible for interpreting the meaning of words (on the left) and recognizing faces and objects (on the right). When these lobes are damaged as they are in FTD, a constellation of symptoms develop, depending on which portions of the brain are affected the most. 

Symptoms of Frontotemporal Dementia

Frontotemporal dementia is sometimes initially diagnosed as a psychiatric disorder because sufferers exhibit bizarre behavior that is totally out of sync with their former selves. Symptoms typically occur in predictable patterns depending on what parts of the brain are involved. According to Mayo Clinic, these include the following:

• Behavior changes
  • Impulsivity and inappropriate social behavior
  • Poor judgment
  • Lack of inhibition
  • Apathy
  • Loss of empathy/insensitivity to the feelings of others
  • Compulsive behaviors, such as tapping or clapping
  • Changes in eating habits, especially a craving for sweets
  • Pica — eating things that are not normally thought of as food

• Language difficulties
  • Trouble finding the right word or understanding written language
  • Difficulty naming common objects
  • Hesitant speech
  • New difficulties with grammar and syntax

• Movement disorders
  • Tremors
  • Stiffness
  • Muscle spasms
  • Lack of coordination
  • Muscle weakness
  • Trouble swallowing

This latter group of symptoms often resembles those of Parkinson’s disease or amyotrophic lateral sclerosis or ALS. And, in fact, research has confirmed that there are genetic and biological similarities between ALS and FTD, although the nature of the connection is unclear at this time.  

Mixed Dementia

As researchers become more familiar with the chemical and structural brain changes associated with dementia, it has become more apparent that the majority of people with symptoms of dementia have more than one underlying disease. Known as mixed dementia, this condition may be a combination of Alzheimer’s disease and vascular dementia, or vascular dementia and other neurodegenerative processes. According to a study of 1000 elderly brains led by Dr. Patrician Boyle, a Professor at the Rush Alzheimer’s Disease Center in Chicago, over 94% had at least one identifiable “neuropathology” (for example, plaques and tangles associated with Alzheimer’s disease, or abnormal deposits of alpha-synuclein as seen in Lewy body dementia.) What’s more, 78% had two or more, 58% had three or more, and 35% had four or more. Further, there was no consistent association between the type of pathology seen and the level of cognitive decline. (The participants had been assessed for cognitive changes over many years before their deaths.) 

Obviously, the medical community still has much to learn about the causes of dementia and the ways in which our brains change as we age. Mixed dementia is probably much more common than we realize, according to Boyle. “Most people who live to be in their 80s will have some combination of neuropathologies in the brain,” she said. “We need to understand how these neuropathologies work together to impair cognition in order to develop effective interventions to prevent cognitive decline in old age.”

Alzheimer’s and Dementia Research

The first major milestone in the history of modern dementia research came in the mid-18th century, when scientists first described cerebral atrophy (shrinking of the brain) in persons who had died at an advanced age (about 35 to 50 years at that time). Later, in 1907, Alois Alzheimer first identified plaques and tangles in the brain of a young woman who had died after developing progressively worsening confusion, memory loss and hallucinations. Alzheimer was reportedly unsure whether these abnormalities caused her symptoms or were a related finding at that time. 

Throughout much of the 20th century, the condition discovered by Alzheimer was considered a rare disorder of younger people, separate from age-related senility (as it was called at that time). But as research continued, the scientific community began to see many similarities between the brains of people with age-related senile dementia and those with Alzheimer’s disease. Eventually, the two were lumped together under the diagnosis of senile dementia of the Alzheimer type.

Today, research into Alzheimer’s disease and other forms of dementia has come a long way. For example, the development of the amyloid PET scan in 2004 now allows doctors to quantify the amount of amyloid deposits in the brains of Alzheimer’s sufferers, even before significant symptoms appear. Not only has this opened up new approaches to following the progress of the disease, it will also enable scientists to track the success of new therapies using objective criteria that heretofore didn’t exist. 

Other avenues of study include the contribution of aerobic exercise to brain health (it’s huge) and the benefits of lowering blood pressure in people at risk for dementia. Additionally, a host of new therapies, from monoclonal antibodies to a vaccine that prevents the formation of tau, are under investigation, and some have already entered clinical trials. 

Alzheimer’s and Dementia Treatment

As of this writing, effective therapies for Alzheimer’s disease and most kinds of dementia are limited, but a number of medicines are available that treat their symptoms. Additionally, The Food and Drug Administration recently approved two medicines that have been shown to slow the progression of early-stage Alzheimer’s disease. They are:

• Aducanumab (Aduhelm®)– Aduhem was the first anti-amyloid antibody approved by the FDA. However, due to concerns about its side effects and high cost, the FDA limited its use to clinical trials. Aduhelm’s manufacturer discontinued manufacturing it in 2023, but the drug will be available to some patients until late 2024. 

• Lecanemab (Leqembi®)– Lecanemab is an anti-amyloid antibody that is delivered via IV infusion every two weeks. It has received full FDA approval for the treatment of early Alzheimer’s disease and mild-cognitive impairment or dementia in people who have confirmed amyloid accumulation in the brain. Like Aduhelm, Legembi is costly (about $26,000 per year, not including administration costs) and its side effects can be severe. Patients receiving the drug require periodic imaging studies to look for side effects such as brain swelling and bleeding in the brain. 

Medications for Symptom Relief

Although no medicine currently available reverses the progression of dementia and Alzheimer’s disease, there are certain classes of drugs that may help with symptoms of memory loss and cognitive difficulties. These include:

• Cholinesterase inhibitors, which are indicated for the treatment of early- to moderate-stage Alzheimer’s disease. These medicines treat symptoms such as memory loss, impaired thinking, poor judgment and language difficulties by preventing the breakdown of the chemical acetylcholine, which helps transmit messages between nerve cells. Drugs in this class include:

• Donepezil (Aricept) 
• Galantamine (Razadyne)
• Rivastigmine (Exelon)

• Glutamate regulators are prescribed for dementia and Alzheimer’s symptoms such as memory loss, inattention, difficulties performing simple tasks, and difficulty with language and reasoning. They act by regulating the activity of the chemical messenger glutamate in the brain. There is only one drug in this class currently approved for moderate to severe Alzheimer’s disease, memantine (Namenda).

Additionally, the medication (Namzaric®), a combination of Donepezil and memantine, is approved for moderate-to-severe Alzheimer’s disease. 

Medications for Behavior and Sleep

In addition to medications to treat memory and cognitive issues, a few medicines are currently approved to address two common symptoms of Alzheimer’s disease and dementia, agitation and impaired sleep. These include:

• Suvorexant (Belsomra®) –  approved for treatment of insomnia in people with mild to moderate Alzheimer’s disease. Possible side effects include impaired alertness and motor coordination (including impaired driving), worsening of depression or suicidal thinking, sleep-walking, sleep-driving and/or sleep paralysis and compromised respiratory function. 

• Brexpiprazole (Rexulti®) –  approved for the treatment of agitation associated with dementia due to Alzheimer’s disease. Rexulti should be used with caution, since serious side effects, including increased risk of death in patients with dementia-related psychosis, may occur. Other unpleasant side effects include sleepiness, weight gain, cold symptoms, and restlessness. 

Conclusion

In conclusion, dementia and Alzheimer’s disease represent significant public health challenges in the U.S. and globally. With an aging population, the prevalence of these conditions continues to rise, placing a growing burden on healthcare systems and caregivers. Research efforts are critical in advancing our understanding of the disease process and developing effective treatments. While no cure currently exists, a few breakthrough medicines show promise in halting progression of the disease. Public awareness and advocacy are essential to improve diagnosis, care, and support for individuals and families affected by dementia and Alzheimer’s disease.