In one of my regular reads of Metafilter, I came across a discussion of paintings done by William Utermohlen as he declined as a result of Alzheimer's Disease. Mr. Utermohlen passed away in 2007, 12 years after his diagnosis. He was able to paint for the first five years of that time. The paintings are very interesting and worth a look.
An earlierMetafilter discussion brought up the topic of using an author's own words to see if they are suffering the effects of Alzheimer's or another dementia.
Telling It Like It Is
Art Stimulates Conversations with Alzheimer's Patients
Easing Alzheimer's Symptoms with Art Therapy
Museum Programs for Alzheimer's Patients Show the Power of Art as Therapy
Longitudinal Detection of Dementia Through Lexical and Syntactic Changes in Writing: a Case Study of Three British Novelists