According to New York-Presbyterian Hospital, "Schizoaffective disorder is an illness in which there are both severe mood swings (mania and/or depression), and some of the psychotic symptoms of schizophrenia. Most of the time mania or depression mix with psychotic symptoms, but there must be at least one two-week period in which there are only psychotic symptoms without any symptoms of mania or depression."
ADAM's description, stripped down to the essentials, is a good one: " Schizoaffective disorder includes elements of both psychosis and mood disorder. ... To be diagnosed with schizoaffective disorder, a person must experience psychotic symptoms - but normal mood - for at least 2 weeks."
Initially a person may be diagnosed as having Bipolar I Disorder with psychotic features if he or she has major manic and/or depressive episodes that include psychotic symptoms such as paranoia, catatonia and hallucinations or others. However, if that person's mood stabilizes but he or she still experiences symptoms of psychosis for at least two weeks, a new diagnosis of schizoaffective disorder is often given.
NAMI points out, "Some people may be misdiagnosed as having schizophrenia. Others may be misdiagnosed as having bipolar disorder. And those diagnosed as having schizoaffective disorder may actually have schizophrenia with prominent mood symptoms. Or they may have a mood disorder with symptoms similar to those of schizophrenia."
The most common treatment for schizoaffective disorder is a combination of mood stabilizing and antipsychotic medications, sometimes with additional antidepressants. As noted by NAMI, since the medications used to treat Bipolar I with psychotic features are generally the same as those used to treat schizoaffective disorder, making the distinction between these two conditions is not of great therapeutic importance. Of far greater impact in terms of proper treatment would be a misdiagnosis of schizophrenia rather than schizoaffective disorder, since the needed mood stabilizer could be left out of the patient's drug therapy.