He has been diagnosed with a rare form of dementia, Creutzfeldt-Jakob disease.
There are only about 300 cases of this disease per year in the US. It's very fast-moving.
Here's what the NIS says about the disease:
CJD belongs to a family of human and animal diseases known as the transmissible spongiform encephalopathies (TSEs). Spongiform refers to the characteristic appearance of infected brains, which become filled with holes until they resemble sponges under a microscope.
One form of the TSEs is mad cow disease.
If you have a relative are struggling with Alzheimer's disease, remember that there are worse fates. One of them is Creutzfeldt-Jakob disease.