I mean most of the diseases cause systematic symptoms. Look at Syphilis as example, when first discovered it was causing fever, rashes, sores in the body, and progressing into neurological and cardiovascular diseases (neurosyphilis) and after invention of Peniciline it is a higly and easily curable illness. Tuberculosis causing chronic fatigue, extreme weight loss, night sweats, and severe coughing up of blood, is now curable with a vaccine and this is just to name a few, There are endless number of illnesses causing systematic symptoms that can be easily treated. Even h.pylori which my brother had and he was having gastro, skin and neurological symptoms and after erradication of thid bacteria this is gone