while diseases like tumor certainly have nothing to do with soul, Is insanity a disease of body or soul?
The only disease of the soul is sin.
So I would say that any disease that can be listed in the Merck Manual is a disease of the body. This includes psychological diseases, since even in the absence of strictly biochemical causes, all emotion has a physical component.
In saying this, I do not mean to separate the body and soul, as human beings, are after all, a unity. We won’t separate the two until death.