Frequency and differential diagnosis of depressive syndromes in schizophrenia.

The frequency, differential diagnosis, and implications of depression occurring in the course of schizophrenia are considered in light of recently reported findings from a follow-up and family study of 500 psychiatric outpatients (the St. Louis 500 Study). Problems in diagnosis are illustrated in an interview of a schizophrenic patient with a history of depression. Nearly 60% of the schizophrenics studied had suffered a depressive syndrome during the course of their schizophrenic illness, supporting the observations of others. The majority of patients with a history of depression who were otherwise diagnosable as schizophrenic had a course of illness consistent with schizophrenia during follow-up. The pattern of illness among first-degree relatives suggested that intercurrent depression did not represent a biologic unity with primary affective disorder. Intercurrent depression should not be overinterpreted in excluding a diagnosis of schizophrenia.