Cognitive impairment is common to both diseases.
Both disorders are typically invisible, making the patient appear to be physically well. The fact of having a severely debilitating chronic disease can in itself cause depression. It is now an accepted fact that most chronic diseases are accompanied by some form of depression. Depression has historically been the specialty of psychiatrists and consequently most general practice physicians are not experts in determining whether the depression they are seeing in a patient is a primary or secondary diagnosis. Depression is also an early warning sign of many other illnesses, including cancer.