If you want to know if his memory is affected by his condition, I'd ask that but I don't think I'd have a right to know what that condition was. Or I'd be saying that regardless of the cause, I needed him to remember what I was bringing to therapy, my name, actions we'd agreed etc and let him sort out how he's going to do that.

Trying to figure out what the condition might be, whether it generally affects memory, whether it specifically affects his memory, whether he might need to retire, might die soon etc etc a keep you away from your own work in therapy. If he's doing something you're not happy with, ask him to stop and if for whatever reason he can't, I'd find someone else but getting tied up in his stuff keeps you out of your stuff, which is the very opposite of therapy.