The Dutch study found that overall, Alzheimer’s disease was the most common cause of young-onset dementia. But when symptoms developed before age 50, early-onset Alzheimer’s was a less likely explanation than two other causes: vascular dementia and frontotemporal dementia.

Vascular dementia results from a blockage or injury to blood vessels in the brain that interfere with circulation and deprive the brain of oxygen and nutrients. Its most common symptoms, in addition to memory problems, are confusion, difficulty concentrating, trouble organising thoughts or tasks, and slowed thinking.

In frontotemporal dementia, portions of the brain that lie behind the forehead and ears shrink, resulting in dramatic personality changes, socially inappropriate or impulsive behaviour and emotional indifference. Movement and memory problems typically develop later in the course of the disease. According to the Mayo Clinic, frontotemporal dementia often begins between the ages of 40 and 65 and may be misdiagnosed as a psychiatric problem.

Lewy body disease is another cause of dementia in younger adults. It is associated with abnormal deposits of a protein called alpha-synuclein in the brain that affects brain chemistry and leads to behavioural, thought and movement problems. Most of the symptoms are similar to those seen in other dementias, and additional symptoms like hallucinations may resemble schizophrenia, but the decline in brain function occurs significantly faster. A distinguishing symptom of Lewy body dementia is having violent dreams and attempting to act them out, Knopman said.

Alzheimer’s disease remains the most common cause of dementia in younger as well as older adults. There is an inherited form of Alzheimer’s that typically arises at younger ages, but those cases account for fewer than 10 per cent of young-onset disease. Most cases of Alzheimer’s occur sporadically, for unknown reasons, though genetic factors may increase risk.

People with Alzheimer’s typically have a build-up of abnormal substances — tau and beta-amyloid proteins — in the brain. Early symptoms include impaired memory, language problems, difficulty concentrating and finishing tasks, poor judgment and visual or spatial deficits that result in problems like driving errors and getting lost. Brain scans may show a loss of brain cells and an impaired ability to metabolise glucose that is indicative of degenerative brain disease.

Probably the most publicised factor known to increase the risk of early dementia is repeated head injuries like those experienced by professional boxers, football and soccer players, and sometimes by military veterans.

Once brain cells are injured or lost, there’s no going back. So preventing head injuries is the best possible protection at the moment.

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Many parents these days try to discourage youngsters from playing sports like football, in which repeated head injuries are common. However, proper and consistent use of helmets and not heading the ball in soccer can limit their risk of head injuries. Knopman said he’s less concerned with primary school children playing such sports; the risk of developing dementia at a young age from repeated head trauma is much greater among those who played Division 1 football or became professional boxers.

Among older adults in general, the same inflammatory factors associated with atherosclerosis, the clogging and hardening of the arteries that nourish the heart, can also afflict blood vessels that feed the brain. Body-wide inflammation linked to diabetes and heart disease can cause brain changes that promote dementia.

Diagnosis of early-onset dementia

Accurately diagnosing young-onset dementia can be difficult and time-consuming and should start with a detailed medical history, Knopman said. “If doctors don’t ask the right questions, families may fail to mention a telltale symptom like violent dreams.”

A thorough cognitive assessment of the person’s memory and language difficulties is critical, he said. Does the person stumble over words or say “white” when he means “black”? Neuropsychological tests can detect subtle difficulties with memory, visual, cognitive and executive functions.

A brain scan is needed to rule out the possibility that a tumour is causing the person’s cognitive symptoms. A spinal tap and analysis of the spinal fluid can reveal elevated levels of tau and beta-amyloid proteins in the brain. An MRI scan can depict shrinkage in specific parts of the brain. And a glucose PET scan can uncover abnormal patterns of sugar uptake in various parts of the brain that can help distinguish between Alzheimer’s disease, Lewy body dementia and frontotemporal dementia. “Different degenerative brain diseases have specific patterns of glucose uptake,” Knopman said.

As with older dementia patients, it’s essential to keep young people with dementia safe. They should no longer drive, operate dangerous equipment, including the stove, or be left alone. All should wear an identifying tag day and night that alerts others to their condition.

This article originally appeared in The New York Times.

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