My husband has vascular dementia. He is complaining of "bugs biting him" and scratching everywhere.

I think server anxiety can cause the feeling of bugs on you. Like a skin crawling feeling, And people with delusions , may think it's bugs.

I went off to research..
I was wondering about kidney function too.

My LO had itch with bug-bite feel. Kidney function was 'ok but not that great', but no actual reason was ever found.

Sadly with many issues in the mix, it may be hard to pinpoint the exact cause here - treating the symptoms may be all you can do.

Lots of folks with Alzheimer's/dementia feel itchy and insist bugs are biting them. I wound up getting my mother a can of Dermoplast which has an anesthetic agent in it. Spray where the itching occurs. YOU do it FOR him, otherwise he's likely to abuse the can and go thru it immediately.

Also keep the protein drinks hidden so he's not drinking 10 a day. The sugar alone in each one is enough to send his blood sugar thru the roof, as a diabetic!

A lot of things can cause itching .
Renal ( kidney failure)
Some leukemias
some diabetics are itchy

Have your doctor investigate the cause .

Not on any opioids?

I would discuss with the MD.

10 protein drinks a day is going to kill him. That alone is 300 grams of protein

I have heard of horrible itching with end stage liver deasses, because of the poisons, in the blood, that the liver isn't filtering out. . Have you called a doctor?