Schneider described schizoaffective disorders as "cases in-between" the traditional Kraepelinian dichotomy of schizophrenia and mood disorders.The historical clinical observation that schizoaffective disorder is an overlap of schizophrenia and mood disorders is explained by genes for both illnesses being present in individuals with schizoaffective disorder; specifically, recent research shows that schizophrenia and mood disorders share common genes and polygenic variations. Schizoaffective disorder was included as a subtype of schizophrenia in DSM-I and DSM-II, though research showed a schizophrenic cluster of symptoms in individuals with a family history of mood disorders whose illness course, other symptoms and treatment outcome were otherwise more akin to bipolar disorder than to schizophrenia. DSM-III placed schizoaffective disorder in "Psychotic Disorders Not Otherwise Specified" before being formally recognized in DSM-III-R. DSM-III-R included its own diagnostic criteria as well as the subtypes, bipolar and depressive. In DSM-IV, published in 1994, schizoaffective disorders belonged to the category "Other Psychotic Disorders" and included almost the same criteria and the same subtypes of illness as DSM-III-R, with the addition of mixed bipolar symptomatology.DSM-IV and DSM-IV-TR (published in 2000) criteria for schizoaffective disorder were poorly defined and poorly operationalized. These ambiguous and unreliable criteria lasted 19 years and led clinicians to significantly overuse the schizoaffective disorder diagnosis. Patients commonly diagnosed with DSM-IV schizoaffective disorder showed a clinical picture at time of diagnosis that appeared different from schizophrenia or psychotic mood disorders using DSM-IV criteria, but who as a group, were longitudinally determined to have outcomes indistinguishable from those with mood disorders with or without psychotic features.
There is no single antipsychotic of choice in treating schizoaffective disorder, but atypical antipsychotics may be considered due to their mood-stabilizing abilities. To date, paliperidone (Invega) is the only antipsychotic with FDA approval for the treatment of schizoaffective disorder. Other antipsychotics may be prescribed to further alleviate psychotic symptoms.Though not approved for treatment use by the FDA, research suggests that Clozapine may also be effective in treating schizoaffective disorder, particularly in those resistant to initial medication. Clozapine is an atypical antipsychotic that is recognized as being particularly effective when other antipsychotic agents have failed. When combined with cognitive therapy, Clozapine has been found to decrease positive and negative symptoms of psychosis at a higher rate in schizoaffective individuals. Clozapine has also been associated with a decreased risk of suicide in patients with schizoaffective disorder and a history of suicidality. Despite this, clozapine treatment may be ineffective for some patients, particularly in those that are already drug-resistant.The management of the bipolar type of schizoaffective disorder is similar to the treatment of bipolar disorder, with the goal of preventing mood episodes and cycling. Lithium or anticonvulsant mood stabilizers such as valproic acid, carbamazepine, and lamotrigine are prescribed in combination with an antipsychotic.Antidepressants have also been used to treat schizoaffective disorder.