One of the most common symptoms of vascular dementia is general cognitive and physical slowing. This likely occurs because the signals in the brain aren’t moving as efficiently through the impaired white matter, Iadecola says. Other symptoms might include difficulty with decision making, problem solving and task execution.

Poor cardiovascular health, particularly high blood pressure, is the biggest risk factor. In fact, an important clue that someone has vascular dementia is a history of heart attack, stroke or high blood pressure. An MRI can help confirm the diagnosis by revealing the white matter damage.

As with any type of neurodegenerative disease, once brain cells are damaged, the symptoms are largely irreversible. But vascular dementia is more preventable than other forms of dementia.

“Let’s try to keep the blood vessels healthy,” Iadecola says. “That’s the best thing we can do right now. We know how to do that better than we know how to fight neurodegeneration.”

Lewy Body Dementia

This type can cause a constellation of symptoms involving the whole body. That’s because it’s “not just something that affects the brain, it affects the nervous system in the periphery as well,” says Dr Sudha Seshadri, the founding director of the Glenn Biggs Institute for Alzheimer’s and Neurodegenerative Diseases at the University of Texas Health Science Centre at San Antonio.

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Some people experience classic cognitive impairment, like problems with executive functioning, though memory loss is less common. Others have visual-spatial difficulties; for example, struggling to locate items in a pantry or judge distances. People may also have striking visual hallucinations.

Physical issues can include constipation, difficulty urinating, lightheadedness when standing up and, in men, erectile dysfunction. Parkinson’s disease symptoms can also occur, such as tremor, muscle rigidity and difficulty with balance.

The overlap with Parkinson’s makes sense because the two conditions are caused by the same dysfunctional protein, alpha-synuclein. The protein clumps into so-called “Lewy bodies” inside neurons, damaging and ultimately killing the cells. A person’s symptoms depend on which areas of the brain are affected first and how the toxic proteins spread.

Doctors tend to rely on a person’s symptoms to make a diagnosis, but that can be difficult because “they’re so different in different patients, and are not always easy to recognise,” says Dr David Irwin, an associate professor of neurology at Penn Medicine. As a result, Lewy body dementia is thought to be underdiagnosed.

Frontotemporal Dementia

This type of dementia is rarer than the other forms, and it tends to emerge earlier in life, with people typically first experiencing symptoms in their 40s, 50s or 60s.

The brain’s frontal lobe, as the name suggests, is one of the areas most affected. Cognitive symptoms often include difficulty with executive functioning, planning or organising. Those problems may become apparent if someone has trouble managing their finances or planning a trip, Irwin says.

Dramatic personality changes can also occur. Some people become uninhibited and impulsive; they may approach strangers or make rude or inappropriate comments. People can also become apathetic and unmotivated, or emotionally cold and distant.

As a result, frontotemporal dementia, or FTD, is often initially misdiagnosed as a psychiatric condition, says Dr Winston Chiong, a professor of neurology at the University of California, San Francisco. A lot of the core symptoms “get attributed to depression or mood or addiction or life events that cause people to behave differently,” he says.

Some people with FTD also experience primary progressive aphasia, or difficulty with speaking and comprehending language.

In the brain, there are two main proteins that become dysfunctional and are associated with FTD. One is TDP-43, which is also involved in LATE and amyotrophic lateral sclerosis, or ALS. The other is tau, but different forms of tau than the one implicated in Alzheimer’s.

LATE

LATE, or limbic-predominant age-related TDP-43 encephalopathy, is a relatively new dementia diagnosis. It first came to light roughly 20 years ago, after scientists observed that many people who died with Alzheimer’s symptoms had toxic clusters of the protein TDP-43 in their brains (sometimes in lieu of amyloid and tau, and sometimes in addition to them).

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As the acronym suggests, LATE is most common in the later decades. Dr Peter Nelson, a professor of pathology at the University of Kentucky College of Medicine, says that roughly a third of people in their 80s and 90s have signs of the disease in their brains.

As with Alzheimer’s, the part of the brain most affected is the hippocampus, and memory loss is the most common symptom. On its own, LATE progresses slowly and “is relatively benign,” Nelson says. But people often have LATE and Alzheimer’s concurrently, which results in “a more swift and severe clinical course,” including anxiety, depression, hallucinations and delusions.

There isn’t a blood test for TDP-43, so doctors can only make a diagnosis based on a person’s symptoms and by ruling out other forms of dementia. The disease is most commonly discovered during an autopsy. The first clinical trial for a treatment for LATE is currently under way.

This article originally appeared in The New York Times.

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