(NYTIMES) - After Ms Maria Turner's minivan was totalled in an accident a dozen years ago, she grew impatient waiting for the insurance company to process the claim.

One night, she saw a red pickup truck on eBay for US$20,000 (S$26,700). She thought it was just what she needed. She clicked "buy it now" and went to bed.

The next morning, she got an e-mail about arranging delivery. Only then did she remember what she had done. Making such a big purchase with no forethought and then forgetting about it was completely out of character for Ms Turner, then a critical care nurse in Greenville, South Carolina. Although she was able to back out of the deal, the experience scared her.

"I made a joke out of it, but it really disturbed me," she said.

It didn't stop her, though. She continued to shop impulsively online with her credit card, buying dozens of pairs of shoes, hospital scrubs and garden gnomes. When boxes arrived, she didn't remember ordering them.

Six years passed before Ms Turner, now 53, got a medical explanation for her spending binges, headaches and memory lapses: Doctors told her that imaging of her brain showed all the hallmarks of chronic traumatic encephalopathy, a degenerative brain disease that can only be definitively diagnosed post-mortem.

It could be linked to the many concussions she suffered as a competitive horseback rider in her youth. Her doctors now also see evidence of Alzheimer's disease and frontotemporal dementia, which affects the frontal and temporal lobes of the brain.

Ms Turner's money troubles aren't unusual among people who are beginning to experience cognitive decline. Long before they receive a dementia diagnosis, many people start losing their ability to manage their finances and make sound decisions as their memory, organisational skills and self-control falter, studies show.

As people fall behind on their bills or make unwise purchases and investments, their bank balances and credit rating may take a hit.

Even during times that aren't complicated by a global health crisis, families may miss the signs that someone is struggling with finances, experts say.

"It's not uncommon at all for us to hear that one of the first signs that families become aware of is around a person's financial dealings," said Ms Beth Kallmyer, vice-president for care and support at the Alzheimer's Association.

Early in the disease, Ms Kallmyer said, dementia robs people of the abilities they need to manage money: "executive functioning" skills, like planning and problem-solving; judgment; memory; and the ability to understand context.

Many people have mild symptoms for years before a diagnosis. During this stage, before obvious impairment, they may make substantial errors managing their finances.

A recent study published in JAMA Internal Medicine found that people with Alzheimer's and related dementia were more likely to miss bill payments up to six years before their diagnosis than were people with no diagnosis.

"We went into the study thinking we might be able to see these financial indicators," said Associate Professor Lauren Hersch Nicholas, a co-author of the study at University of Colorado.

"But we were sort of surprised and dismayed to find that you really could. That means it's sufficiently common, because we're picking it up in a sample of 80,000 people."

For decades, Mrs Pam McElreath kept the books for the insurance agency that she and her husband, Jimmy, owned. In the early 2000s, she started having trouble with routine tasks.

She assigned the wrong billing codes to expenditures, filled in cheques with the wrong year, and forgot to pay the premium on her husband's life insurance policy.

"But it's not like my friend that made that one mistake, one time," Mrs McElreath, 67, said. "Every month, I was having to correct more mistakes. And I knew something was wrong."

She received diagnoses of mild cognitive impairment in 2011, at age 56, and early-onset Alzheimer's two years later. In 2017, doctors changed her diagnosis to frontotemporal dementia.

Getting a devastating diagnosis is hard enough, but learning to cope with it is also hard. Eventually, both Mrs McElreath and Ms Turner put mechanisms in place to keep their finances on an even keel.

Ms Turner, who has two adult children, lives alone. After her diagnosis, she hired a financial manager, and together they set up a system that provides her with a set amount of spending money every month and doesn't allow her to make large withdrawals on impulse.

She ditched her credit cards and removed eBay and Amazon from her phone.

In 2017, the McElreaths sold their insurance agency to spend more time together and moved west to Sugar Grove, in the Blue Ridge Mountains. They worked with a therapist to figure out how to ensure that Mrs McElreath can keep doing as much as possible.

These days, she still signs their personal cheques, but now her husband looks them over before sending them out. The system is working so far.

"At first, I was mad, and I went through this dark time," she said.

Her husband's gentle approach helped. "He was so good about telling me when I did something wrong but doing it in such a kind way, not blaming me for making mistakes," she said. "We've been able to work it out."