Cycloid psychoses as atypical psychoses: 'concordance' and 'discordance'

The term 'atypical psychosis' coined by Mitsuda in 1942 describes a group of psychosis that show similarities to schizophrenia as well as manic-depressive diseases. It is controversial whether it refers to a uniform group of diseases exposing typical characteristics. According to Leonhard a typical uniform group of cycloid psychoses can be contrasted with a group of atypical schizophrenias. The position of the so-called atypical psychoses in the sense of a nosological position within the classification systems of different psychiatric schools will be analyzed and discussed.