Can I have a tax deduction if I care for my husband full time who has early onset dementia?

There's no deduction that is as specific as that that I know of. You should check with a tax expert for this, as situations differ. His medical expenses should be deductible but as far as a deduction for caring for him vs. a paying outside job, I'm not sure that you'd come out that well financially. I wish you the best. Please get advice from a specialist in this field.
Carol