Is a dementia diagnosis grounds for divorce?

There is nothing easy about caring for a spouse with dementia – someone who can't eat on his own, or follow a conversation or even be left alone for fear she will start a fire or wander off.

But when does it get so hard that you have permission to call the marriage quits?

Religious broadcaster Pat Robertson says divorcing a spouse with Alzheimer's is morally justifiable, calling the disease a "kind of death."

During his live television show, Mr. Robertson was asked by a viewer what to tell a friend who had started dating another woman after his wife was diagnosed with Alzheimer's.

Mr. Robertson said he wouldn't "put a guilt trip" on someone who divorces a spouse with the illness. "I know it sounds cruel," the former Baptist minister said, "but if he's going to do something, he should divorce her and start all over again, but make sure she has custodial care and somebody looking after her."

Where does this leave the vow to stay married until "death do us part?" Alzheimer's, which is a progressive neurological disorder that can't be cured, is a form of death, Mr. Robertson explained.

A spokesperson for the Alzheimer's Association said it is uncommon for couples to divorce as one partner progresses through an Alzheimer's diagnosis. But other research suggests this may not be true for illnesses such as cancer, and that men may be more likely to bail than women.

A study published in 2009 found that a woman is six times more likely to be separated or divorced soon after a diagnosis of cancer or multiple sclerosis than if a man in a relationship is the patient. (Longer marriages were more likely to last.)

Despite the hardship of Alzheimer's, many spouses offer a different perspective.

Gary Grais of Vancouver, interviewed for The Globe and Mail's Dementia series in 2010 , described the isolation of living with a woman who could no longer dress herself or cook, and who barely spoke any more. But, he said, "I am not putting her in a home until I absolutely have to."

Donna MacDiarmid, another subject of the series, drove every day to feed her husband, Roger, in his Fredericton, N.B., nursing home, staying each night until he was tucked into bed.

"What I am doing is not a sacrifice," she said. "This is the time I have with him. It's what we have left that is intimate and special."

How long do you stay, and when is it all right to go? Perhaps that's a marriage discussion worth having before you need to make the decision on your own.

Is it okay to leave a spouse declining with an Alzheimer's diagnosis? What about other diseases? What would you want your spouse to do in that situation?