To deduct medical expenses for him he has to qualify as your dependent and also must have an ITIN. To deduct medical expenses you must itemize deductions and only an amount of total medical expenses greater than 7.5 percent of your AGI can be deducted.
taxpayers can deduct medical expenses paid for some individuals who don't qualify as their dependent, such as a parent for whom the taxpayer provided over half the support but the parent's gross income exceeded $4200 for 2019. so in such a case you can deduct his medical expenses but he is not a dependent. IRC 213(a)
from PUB 502
Whose Medical Expenses Can You Include?
Qualifying Relative
A qualifying relative is a person:
1. Who is your:
c. Father, mother, or an ancestor or sibling of either of them
2. Who wasn't a qualifying child of any taxpayer for 2019, and
3. For whom you provided over half of the support in 2019.
the PUB suggests you can claim the expenses if you provided over 1/2 his support.
but without an ITIN or SSN you can't claim him as a dependent.