There is a common myth that people with Alzheimer's are completely incompetent and cannot be trusted to make their own decisions. It is not true as the early stages of the disease are relatively mild.
People who are diagnosed with the disease early enough can still make their own decisions. However, as the disease progresses most do eventually lose the ability to make their legal decisions as NorthJersey.com points out in "Planning becomes vital following Alzheimer's diagnosis."
The article suggests that people who receive an Alzheimer's diagnosis should get a general durable power of attorney, a health care power of attorney and a living will.
The powers of attorney will allow the person to appoint someone else to handle financial and medical affairs, respectively, when the Alzheimer's patient is no longer able to do so. The living will is used to give advanced directives about what type of treatments doctors should employ to keep the patient alive.
These are important documents to have.
Getting them after an Alzheimer's diagnosis is solid advice. However, even better advice is not to wait until after receiving such a diagnosis. All three documents are part of general estate planning. There is no need to wait until you know you will need them to get them.
Plan ahead and get them now before an issue of competency is raised.
Reference: NorthJersey.com (Dec. 27, 2015) "Planning becomes vital following Alzheimer's diagnosis."