Dementia is a brain disease that can be caused by a number of health conditions. Sometimes called “major neurocognitive disorder,” dementia is diagnosed when a person has a slow and progressive decline in their memory or other areas of cognitive function, as well as their ability to communicate, plan, care for themselves, or behave in their usual manner.

Doctors refer to mild symptoms of memory or cognitive decline as mild cognitive impairment, which can cause confusion and memory lapses. Although mild cognitive impairment may not always progress, older adults with the condition are at increased risk of developing dementia. For instance, about 15% of people over 65 with mild cognitive impairment develop dementia within two years.

Dementia typically affects people after age 65, and the risk of dementia increases as people age. About 1% to 2% of adults ages 65 to 69 have dementia, while between 20% and 25% of adults ages 85 to 89 have dementia. An even higher percentage of people in their 90s and 100s have the condition. And, as people are living longer, a greater percentage of the population will eventually be diagnosed with dementia.

As dementia progresses, it advances to the point where a person is unable to handle their most basic needs, including eating, communicating, and using the restroom. There is no cure for dementia, but some treatments can help to provide support, improve safety, and delay symptoms.

Dementia is an umbrella term that refers to a loss of brain function caused by a variety of conditions that affect capabilities like remembering, thinking, speaking, understanding others, and acting in socially acceptable ways. It is different from the occasional forgetfulness that can occur among older adults, and it is not a normal part of aging.

Dementia causes people to become unable to take care of themselves adequately and leads to a loss of independence over time. In most cases, their loved ones notice a change and suggest they see a doctor; those with dementia sometimes do not recognize their own symptoms. The rate of functioning and cognitive decline varies, depending on the type of dementia, but when a person has dementia, their ability to function physically and cognitively will continue to decline gradually over years, leading to death.

Common forms of dementia include:

• Alzheimer’s disease, the most common cause of dementia, which affects a person’s memory, language, and cognitive function
• Vascular dementia, which typically occurs in people who have had a stroke or experienced damage to blood vessels in the brain
• Lewy body dementia, which commonly causes decline in cognitive function, as well as slowed walking, stiffness, and impaired balance. It may cause hallucinations and sleep problems.
• Frontotemporal dementia, which typically causes personality, behavioral and language changes
• Mixed dementia, the term that describes when there is more than one underlying cause of dementia

Other conditions that may cause dementia include:

• Huntington’s disease
• Parkinson’s disease
• Multiple sclerosis
• Multiple sclerosis
• Progressive supranuclear palsy
• Creutzfeldt-Jakob disease
• HIV
• Syphilis
• Other brain infections

Some health conditions can cause dementia-like symptoms, which can sometimes be reversed with intervention, such as:

• Brain tumors
• Delirium (acute confusion)
• Normal pressure hydrocephalus
• Alcohol use disorder
• Significant shifts in blood sugar levels associated with diabetes
• Changes in levels of sodium or calcium in the blood
• Low levels of vitamin B12

As adults age, they occasionally forget details or have trouble recalling a friend’s name. Age-related changes in memory and thinking progress very slowly and do not impair a person’s ability to function independently. The memory changes and other symptoms associated with dementia progress faster and are more severe.

When a person has dementia, changes take place in areas of the brain involved with memory, cognitive functioning, and behavior. They are not a normal, natural part of aging, and they can’t be reversed by lifestyle changes or medication. Different symptoms may occur depending on the underlying cause of dementia for a specific person.

Dementia is caused by changes that arise in the brain, which damage or interrupt connections between neurons (nerve cells in the brain that communicate with each other). Although doctors and researchers aren’t sure of the exact reason this occurs, there are leading theories for what contributes to these changes.

Alzheimer’s disease. In patients with Alzheimer’s disease, doctors believe that substances known as plaques and tangles cause brain changes. Abnormal, sticky protein deposits—known as beta-amyloid plaques—and protein deposits within neurons—known as tangles—block communication between neurons and damage nerve cells.

Vascular dementia. In patients with vascular dementia, decreased blood flow to the brain—commonly from a stroke or repeated small strokes—leads to brain changes that cause memory loss and cognition issues.

Lewy body dementia. In patients with this condition, abnormal protein deposits, known as Lewy bodies, arise in the brain, causing changes in cognition and difficulty with walking and balance.

Frontotemporal dementia. In patients with frontotemporal dementia, several abnormal protein substances have been found in the brain, which may contribute to the progression of the disease. People may experience personality changes or have trouble speaking or understanding others.

Depending on the type of dementia, people may experience symptoms such as:

• Difficulty remembering recent events, people’s names, and important dates
• A decline in the ability to reason or problem-solve
• A pattern of making poor judgments
• Losing the ability to understand the consequences of one’s actions

• An inability to follow instructions or complete tasks
• Withdrawing from people and activities that once brought the person joy
• Losing interest in personal hygiene and self-care, food, and the world around them
• Increased irritability
• Rapidly shifting emotions
• Losing track of time
• Difficulty finding words while speaking
• Difficulty understanding what others are saying
• A tendency to get lost or wander away from home
• Personality changes
• Exaggeration of personality traits
• Paranoid thoughts
• Increased confusion, agitation, or anxiety, especially in the evening
• Difficulty falling asleep or staying asleep

As dementia becomes more advanced, additional symptoms may arise, such as:

• Not being able to recognize relatives or close friends
• Loss of bladder and/or bowel control
• Unsteadiness that leads to falls
• Getting lost in one’s own home
• Losing the ability to speak
• Forgetting how to feed yourself, chew, and swallow
• An inability to get out of bed

A small percentage of people with dementia experience hallucinations, delusions, and/or paranoia.

Dementia typically arises in older adults, so increased age is a risk factor. Other risk factors of dementia include:

• A family history of dementia
• A personal history of depression, loneliness, social isolation, and/or mild cognitive impairment
• Being diagnosed during one’s 40s or 50s with type 2 diabetes, high blood pressure, or high cholesterol levels
• Personal history of stroke or atrial fibrillation
• Having gene variants linked to dementia, including the APOE ε4 allele, which increases the risk of Alzheimer’s disease

Doctors may diagnose dementia after obtaining a medical history, performing a physical exam, and offering diagnostic tests. A primary care physician may be able to diagnose dementia, but a psychiatrist, neurologist, or geriatrician with subspecialty training in cognitive disorders evaluation and treatment may be needed.

When dementia is suspected, patients often visit the doctor with a family member, who may be able to share deeper insights and information about the patient. The family member should tell the doctor about the symptoms the patient has experienced, including details about how long they have noticed the problems, how quickly they progressed, and whether the patient has lost interest in activities they normally find enjoyable. It’s also important to mention if there is a personal history of depression or a family history of dementia. Be sure to mention any medications the patient takes and any health conditions they have.

During a physical exam, doctors may offer neuropsychological testing to see how well a patient’s brain functions. Testing assesses a patient’s ability to recall information, solve problems, pay attention, reason, and use language appropriately. The test results can show whether a patient has normal cognitive functioning or a decline in cognitive function that may indicate mild cognitive impairment or dementia.

Doctors who suspect dementia may order one or more of the following diagnostic tests:

• A magnetic resonance imaging (MRI) scan of the brain, which can show structural brain changes
• A computed tomography (CT) scan or X-ray of the brain to look for abnormalities or changes
• Blood tests to rule out thyroid problems, vitamin B12 deficiency, and other conditions
• A lumbar puncture to check for common causes of dementia or dementia-like symptoms

There is no cure for dementia, although medications may slow the progression of the disease. Symptoms of dementia progress over time.

When a patient is diagnosed with dementia, they should take an active role in planning for their future care, naming relatives or close friends as financial power of attorney (to make financial decisions on their behalf when they are unable to make decisions on their own) and medical power of attorney (to make health care decisions on their behalf when they are unable), and creating an advance directive or living will that details their financial and health care preferences. Family members should involve the patient with dementia in decision-making for as long as the patient is able to participate in these conversations.

As dementia progresses, patients ultimately become unable to care for themselves and need around-the-clock care. Some patients with dementia are able to remain at home with assistance. Other patients move to an assisted living facility or nursing home. People in the later stages of dementia at a higher risk for infections—the most common cause of death in someone with dementia is pneumonia.

“Our teams at Yale offer comprehensive evaluations and testing to determine the cause of dementia, which is essential to guide conversations about possible treatments and expectations of disease progression,” says Adam Mecca, MD, PhD, a Yale Medicine geriatric psychiatrist who specializes in memory disorders including Alzheimer’s disease, dementia, mild cognitive impairment, and other related conditions. “Importantly, we focus on the unique needs of each patient to help provide appropriate social and functional support.”