The issue isn't whether you can refuse hospitalization -- which you can do without hospice intervention -- or whether you can opt for palliative care. It's how much of the tab Medicare will pick up.
Hospice is for those who are terminally ill and sick enough that they are expected to die within six months. Because they are expected to die, most hospice programs forego extensive life-prolonging treatments, so that hospice patients can concentrate on getting the most out of the time they have left, without the negative side-effects that life prolonging treatments can have. As Audrey notes, life expectancy can be difficult to predict in an Alzheimer's patient. Once the doctor agrees there are so many co-morbidities that life expectancy is thought to be 6 months or less, s/he will authorize hospice care. As long as the patient continues to need hospice treatment, the patient can continue to receive it. I have friends whose loved ones have been on hospice for more than three years. Medicare pays for hospice care, whether in the home or in a hospice facility. This care includes a lot of "extras" that Medicare would not usually cover -- incontinence supplies, medicines, chaplain, home health nursing visits, etc. That's why a doctor's authorization is needed.
OK, but what if the doctor feels your loved one has a longer life expectancy than that? How do you get "comfort care" for your loved one, supervised by a doctor, and avoid unnecessary and distressful hospitalizations?
Palliative care is appropriate for patients who have life-altering, but not necessarily life-threatening, disorders. It can be received by patients at any time, at any stage of illness whether the illness is terminal or not. Palliative care has the same focus on quality of life as hospice, but there is no expectation that life-prolonging therapies will be avoided -- the patient may choose the treatments s/he desires.
Some palliative care specialists see their more mobile patients in the office, and their less mobile at home. Some places offer a palliative care program that is like hospice, in that all of the care providers (nurse practitioner, nurse, chaplain, etc) come to your home. Palliative care is often provided by an organization that provides hospice care.
The big differences from hospice, then, are (a) you do not need to have anyone's authorization to choose palliative care, (b) the palliative care patient can opt for "curative" treatments at will, and (c) Medicare may not pick up the full tab.
My husband is being cared for by a certified geriatrician who is a palliative care / hospice care specialist. He sees her at her office (a senior healthcare center), and those visits are covered by Medicare, just like a "regular" doctor's. As his disease progresses, we will transition to at-home palliative care services, with the palliative care team supervised by the same doctor. I love her to pieces. She focuses on what's important for his quality of life. And both she and the rest of staff at the center really know how to work with Alzheimer's patients.