You searched for: “idiopathically
idiopathically (adverb) (not comparable)
Pertaining to how diseases arise entirely within organs: Some illnesses appear idiopathically, as opposed to those that are the result of outside influences.

A disease of unknown cause, or a morbid state developing from a spontaneous origin which is not preceded by or caused by any other disease, can develop idiopathically in a person's body.