[Differential diagnosis of first episode psychosis: importance of optimal approach in psychiatric emergencies].

OBJECTIVE To review the literature regarding the diagnosis of first episode psychosis in the context of emergency psychiatry. METHOD Review of empirical and review articles selected by electronic search in the database PubMed. RESULTS Specific features of emergency care--single, brief and cross section assessment, and with little information--may jeopardize the diagnostic process. These limitations can be circumvented by application of operational diagnostic criteria, the use of scales and structured interviews and a short period of observation, between 24-72 hours. Diagnoses of bipolar disorder, schizophrenia, psychotic depression and delusional disorder developed in the context of emergency have good stability, but not the diagnoses of brief psychotic disorder, schizophreniform disorder and schizoaffective disorder. First episode psychosis can occur in the course of the use of psychoactive substances, with relatively frequent maintenance of psychotic symptoms even after cessation of the use of the substance. The rational use of subsidiary tests may help the differential diagnosis of psychotic episodes due to general medical conditions. CONCLUSION Diagnoses of first psychotic episode can be adequately performed during psychiatric emergencies, if routines are implemented based on scientific evidence.