Researchers have outlined a syndrome called "mild behavioural impairment" where behaviour changes could indicate dementia may be brewing.

Memory loss may not always be the first warning sign that dementia is brewing - changes in behaviour or personality might be an early clue.

Researchers on Sunday outlined a syndrome called "mild behavioural impairment" that may be a harbinger of Alzheimer's or other dementias, and proposed a checklist of symptoms to alert doctors and families.

Losing interest in favourite activities? Getting unusually anxious, aggressive or suspicious? Suddenly making crude comments in public?

"Historically those symptoms have been written off as a psychiatric issue, or as just part of ageing," said Dr Zahinoor Ismail of the University of Calgary, who presented the checklist at the Alzheimer's Association International Conference in Toronto, Canada.

Now, "when it comes to early detection, memory symptoms don't have the corner on the market anymore", he said.

Alzheimer's, the most common form of dementia, gradually strips people of their memory and the ability to think and reason.

But it creeps up, quietly ravaging the brain a decade or two before the first symptoms become noticeable.

Early memory problems called "mild cognitive impairment", or MCI, can raise the risk of later developing dementia, and worsening memory often is the trigger for potential patients or their loved ones to seek medical help.

It's not uncommon for people with dementia to experience neuropsychiatric symptoms, too - problems such as depression or "sundowning", agitation that occurs at the end of the day - as the degeneration spreads into brain regions responsible for more than memory.

And previous studies have found that people with mild cognitive impairment are at greater risk of decline if they also suffer subtler behavioural symptoms.

Ismail is part of an Alzheimer's Association committee tapped to draft a checklist of the symptoms that qualify - new problems that linger at least six months, not temporary symptoms or ones explained by a clear mental health diagnosis or other issues such as bereavement, he stressed.

They include apathy, anxiety about once routine events and flaunting social norms. He even cites extreme cases, like a 68-year-old who started using cocaine before anyone noticed her memory trouble.

If validated, the checklist could help doctors better identify people at risk of brewing Alzheimer's and study changes over time.

Technology specialist Mike Belleville of Douglas, Massachusetts, thought stress was to blame when he found himself getting easily frustrated and angry. Normally patient, he began snapping at co-workers and rolling down his window to yell at other drivers, "things I'd never done before", Belleville said.

The final red flag was a heated argument with his wife, Cheryl, who found herself wondering, "Who is this person?"

When Mike Belleville didn't remember the strong words the next morning, the two headed straight for a doctor.

Eventually Belleville, now 55, was diagnosed with an early-onset form of dementia - and with medication no longer gets angry so easily, allowing him to volunteer his computer expertise.