By Paula Span for the New York Times

It’s difficult for physicians to determine with much precision how long anyone with a terminal disease can expect to live, but it’s particularly challenging when the disease is advanced dementia.

“People with dementia get sicker inch by inch,” said Lin Simon, director of quality at Gilchrist Hospice in Baltimore, the largest hospice organization in Maryland. “Trying to say, ‘Now, she’s ready for hospice’ is much harder.”

Yet doctors serve as the gateway to hospice, which provides palliative care for the dying and support for their families. Medicare regulations require a physician to certify that a patient entering hospice is likely to die of his or her disease within six months. Doctors are more likely to do so when the disease is cancer or heart failure, which have more predictable trajectories.

That’s the major reason that dementia patients are under-enrolled in hospice programs.

Only 11 percent of Americans who died in hospice care last year had a primary diagnosis of dementia, according to statistics from the National Hospice and Palliative Care Organization — up from 7 percent eight years earlier, but still a small proportion given the country’s galloping rates of dementia.