When Ann Vandervelde visited her primary care doctor in August, he had something new to show her.

Dr. Barak Gaster, an internist at the University of Washington School of Medicine, had spent three years working with specialists in geriatrics, neurology, palliative care and psychiatry to come up with a five-page document that he calls a dementia-specific advance directive.

In simple language, it maps out the effects of mild, moderate and severe dementia, and asks patients to specify which medical interventions they would want — and not want — at each phase of the illness.

“Patients stumble into the advanced stage of dementia before anyone identifies it and talks to them about what’s happening,” Dr. Gaster told me. “At what point, if ever, would they not want medical interventions to keep them alive longer? A lot of people have strong opinions about this, but it’s hard to figure out how to let them express them as the disease progresses.”

One of those with strong opinions, it happens, was Ms. Vandervelde, 71, an abstract painter in Seattle. Her father had died of dementia years before, in a nursing home after her mother could no longer care for him at home. Ms. Vandervelde had also spent time with dementia patients as a hospice volunteer.