If your son cannot be your dependent because he had more than $4,000 of gross income, but otherwise would have qualified as your dependent (basically that you & other family members provided more than half his support), then you can include in your deductible medical expenses any qualifying medical expenses you paid on his/her behalf just as if he/she was your dependent. The $20,000 you provided would count as support provided by your for this rule (the medical dependent rule)
