He became increasingly demented!

Tom is demented.

You're demented.

He's demented.

I think Tom is demented.

In relating the circumstances which have led to my confinement within this refuge for the demented, I am aware that my present position will create a natural doubt of the authenticity of my narrative.

Although there was once believed to be a causative relationship between syphilis and artistic genius, I would hope that the vast majority of modern artists and writers are reasonable enough to avoid becoming infected just on the off chance that neurosyphilis dementia might improve the quality of their work.

Donald Trump is suffering from dementia.

Among very old dogs, up to two thirds of them show signs of dementia.

I'm in difficulties because of the demented old woman next door wreaking havoc in my fields.