Signs of Sir Terry Pratchett’s dementia may have been present in his writing a decade before his official diagnosis, new research has found. Researchers have examined the lexical diversity—a measure of how varied an author’s word choices are—of 33 books from Pratchett’s Discworld series, focusing specifically on his use of nouns and adjectives.

The study found that Pratchett’s language in “The Lost Continent,” written almost 10 years before his diagnosis of posterior cortical atrophy (PCA), a rare form of Alzheimer’s, showed a significant decline in the complexity of the language used compared to his previous works.

The research team hopes that the study may aid in the early detection of dementia, for which there is currently no cure. The work is published in the journal Brain Sciences.