If a person writes in their autobiography that they have a “pathological (mental) disease,” they have made this condition a matter of public record. If the person then wants to be POTUS, it’s unreasonable to imagine the pathological mental disease won’t be mentioned. You refuse to say how you would explain these terms to an audience that may not grasp their significance. It is a fair question, though, and a practical one under the circumstances.
Again, I have no psychological expertise, nor do I see the need to explain it. But I am certain that it can be done without having to compare Carson to a child molester. And it is disingenuous for a Trump supporter to condemn Cruz for something one of his campaign workers did while giving Trump a free pass for doing much worse.