A poor prognosis was assumed to apply to these patients by most clinicians, and this poor prognosis was harmful to many patients. The poor prognosis for DSM-IV schizoaffective disorder was not based on patient outcomes research, but was caused by poorly defined criteria interacting with clinical tradition and belief; clinician enculturation with unscientific assumptions from the diagnosis history (discussed above), including the invalid Kraepelinian dichotomy; and by clinicians being unfamiliar with the scientific limitations of the diagnostic and classification system.The DSM-5 schizoaffective disorder workgroup analyzed all of the available research evidence on schizoaffective disorder, and concluded that "presenting symptoms of psychosis have little validity in determining diagnosis, prognosis, or treatment response." Given our understanding of overlapping genetics in bipolar disorders, schizoaffective disorder, and schizophrenia, as well as the overlap in treatments for these disorders; but given the lack of specificity of presenting symptoms for determining diagnosis, prognosis or treatment response in these psychotic illness syndromes, the limits of our knowledge are clearer: Presenting symptoms of psychosis describe only presenting symptoms to be treated, and not much more. Schizoaffective disorder was changed to a longitudinal or life course diagnosis in DSM-5 for this reason. Research
Little is known of the causes and mechanisms that lead to the development of schizoaffective disorder.
Poorly trained clinicians used the diagnosis without making necessary exclusions of common causes of psychosis, including some prescribed psychiatric medications. Specialty books written by experts on schizoaffective disorder have existed for over eight years before DSM-5 describing the overuse of the diagnosis.Carpenter and the DSM-5 schizoaffective disorders workgroup analyzed data made available to them in 2009, and reported in May 2013 that:
a recent review of psychotic disorders from large private insurance and Medicare databases in the U.S. found that the diagnosis of DSM-IV schizoaffective disorder was used for about a third of cases with non-affective psychotic disorders. Hence, this unreliable and poorly defined diagnosis is clearly overused. As stated above, the DSM-IV schizoaffective disorder diagnosis is very inconsistently used or unreliable. A diagnosis is unreliable when several different mental health professionals observing the same individual make different diagnoses excessively. Even when a structured DSM-IV diagnostic interview and best estimate procedures were made by experts in the field that included information from family informants and prior clinical records, reliability was still poor for the DSM-IV schizoaffective diagnosis.The DSM-IV schizoaffective diagnosis is not stable over time either. An initial diagnosis of schizoaffective disorder during time spent at a psychiatric inpatient facility was stable at 6-month and 24-month follow ups for only 36% of patients. By comparison, diagnostic stability was 92% for schizophrenia, 83% for bipolar disorder and 74% for major depression.