These symptoms however can sometimes be late-arriving features. They are changing all the time. Sometimes they are not present at all. They tell us little about causation, but indicate that the brain chemistry has been disturbed in such a way that alterations in mood, thought and behaviour develop due to a disease whose cause is unknown. Hemmings4 has said that these diagnostic systems may perhaps be a snare and a delusion and that they are not as scientifically based as is sometimes thought.
Many bodily diseases can cause psychiatric symptoms.
There is no single psychiatric symptom that is specific for schizophrenia. It seems to us, in SAGB, that schizophrenia is an umbrella disease under which many medical conditions shelter because they have similar psychiatric symptoms but each of which has a different cause, usually arising in the body, but sometimes in the brain. An analogy which will be familiar to all is that of fever which can have many different causes and in itself can rarely point to any specific cause. Shiffer6, et al have written a valuable reference book on The Medical Evaluation of the Psychiatric Patient. The medical conditions were often found to be the cause of, or the exacerbators of, the psychiatric symptoms.