Loss of smell related to dementia, Parkinson’s disease

The nerves in our nasal cavity send signals to our brain to alert us to what we are feeling. As we age, our sight, hearing and smell decline. When we lose our ability to distinguish one scent from another, say vanilla versus cinnamon, it can be an early sign of dementia or Parkinson’s disease, a 2018 study in Current Asthma and Allergy Reports and a 2016 study in Neurology find.

We may temporarily lose our sense of smell, for example from a viral infection like the common cold, the flu, or COVID-19, but it usually comes back. Poor scent identification in adults – the ability to distinguish one scent from another versus the overall ability to smell – has been linked to a significant increased risk of subsequent dementia, according to a 2020 study in Frontiers in neuroscience.

Early diagnosis

The loss of the ability to identify smells signals dysfunction in the region of the brain responsible for identifying and naming smells, says Devangere P. Devanand, professor of psychiatry and neurology at Columbia University Irving Medical Center. But more research is underway.

“We don’t know enough about what changes in odor can mean for a person’s overall risk,” says Devanand. About 4% of the population, since childhood, cannot identify smells, but that has nothing to do with dementia, he adds.

When a patient notices a decrease in their ability to identify odors, Devanand presents them with a test consisting of 12 scratch and sniff samples; they are asked to identify flavors such as pizza, apple, coffee and gasoline. The tests are usually given when a patient or a family member notices slight deficits in memory and odor identification, he says. If someone scores poorly on the odor identification test and shows memory loss during the test, this will trigger additional tests to confirm the diagnosis. If they do well on an odor identification test and agree on a memory test, the patient can wait and follow up later or, if still worried, have more tests, he said.

Although there is no cure for dementia or Parkinson’s disease, the odor identification test can lead to an early diagnosis. An ear, nose and throat doctor can examine the patient’s nasal tissues under a microscope and look for telltale signs of Alzheimer’s disease or another type of dementia, says Johannes Reisert, faculty member of Philadelphia. Monell Center, an independent, non-profit scientific institute dedicated to research into the senses of taste and smell. Because scent decline precedes other symptoms, he says, “it could lead to an earlier diagnosis.”

Early diagnosis “is extremely important,” says Heather Snyder, vice president of medical and scientific relations for the Alzheimer’s Association. It allows people to create their plans for their health care and personal finances. Participation in clinical trials is more feasible in the early stages of the disease, and participation in trials gives patients access to emerging treatments “that may be appropriate at an early stage of the disease,” she says.

It helps for family members to know the diagnosis, as the behavior of some patients with dementia changes, says Devanand. “Family members get really upset when they don’t realize this is happening.” Those who lose their scent identification should speak to a doctor who takes their concerns seriously and investigates them, he says.

Delay progress?

“There is no established way to delay the onset of dementia. There are things that people can do that may have a very small effect, ”says Devanand, especially exercising regularly, eating the Mediterranean diet and stimulate the brain.

“Exercise and fitness are also important. We do not know if improving fitness, which has been shown to have a weak effect on cognitive performance, decreases the risk of small or mini-strokes in the brain, or if it is more specific for. reduce the risk of developing Alzheimer’s disease, ”says Devanand.

Specifically, the guidelines call for at least 30 minutes of moderately intensive exercise at least three days a week, says Carolyn Fredericks, neurologist at Yale Medicine. The studies showing a cognitive advantage were based on the type of exercise that makes you breathe heavily and makes your heart beat, she says.

The Mediterranean diet has also been shown to help cognition, says Fredericks. She advises her patients to eat as they would if they were on vacation on the Italian coast – lots of fish, lean protein, beans, vegetables with protein, fruits and dark leafy greens “which appear to have specific advantages in preserving cognitive functions. And olive oil rather than butter, and whole grains, ”she says. “It’s really not a restrictive diet at all, but rather a style of eating that seems to be really good for the brain.”

Again, says Devanand, it’s not clear whether the benefits of this diet lower the risk of small strokes, which occur with aging and can affect cognition, or whether the diet directly prevents or delays disease. ‘Alzheimer’s.

Although studies have been done on brain games, anything people do to exercise and stimulate their brains and increase brain activity “helps reduce the likelihood of being diagnosed with the disease,” he says. Learning new skills, keeping your brain engaged, and socializing all contribute to cognition. Brain exercise “builds up cognitive reserves. You have more intellectual capacities to the extent that they compensate for the memory loss you face,” Devanand explains. “It really is a way to improve your resilience when you contract the disease. “

Drugs approved for the treatment of Alzheimer’s disease improved cognitive abilities, including performance of memory tests, to a very small extent compared to placebo in clinical trials, says Devanand, citing a recently published study. in June 2021 in Neuropharmacology. However, the drugs used to treat Alzheimer’s disease, he says, “don’t really change the long-term course of the disease.”

The controversial aducanumab, which has received accelerated approval from the United States Food and Drug Administration, was shown in two studies to reduce plaque buildup in the brain, he says, but clinical measures showed a small effect in one study and no effect in the other study. Doctors’ offices including Devanand, the Cleveland Clinic and the Mount Sinai Health System in New York City have said they will not prescribe it.