The dichotomy which shows the polymorphism
The existence of acute psychoses of short duration, often having intense or even dramatic symptomatology, but also full remission, has always been well known to clinicians and has been described by almost all important authors of the Pre-Kraepelinian period. Its relevance became still greater after Emil Kraepelin's division of the so-called endogenous or functional psychoses into a group of dementia praecox (i.e. schizophrenia) and manic-depressive insanity (mood disorders) (Kraepelin, 1893, 1896, 1899). Kraepelin based this dichotomy mainly on symptomatology, course and longitudinal outcome.
Mood disorders (i.e. manic-depressive insanity) are characterised according to Kraepelin by:
severe depression or exaltation, or by a mixture of both (mixed states),
a periodic or phasic course, and
a favourable long-term outcome.
Kraepelin's dementia praecox is characterised by:
mood incongruent delusions and hallucinations,
disturbances of volition, thinking or of affectivity,
chronic and deteriorating course with an unfavourable outcome.
Kraepelin knew, of course, of Brief and Acute Psychoses: vivid descriptions of these disorders can be found in chapters on mixed states and, particularly, on delirious mania (Kraepelin, 1899/1990, see also below). Kraepelin allocated them according to the above-mentioned diagnostic criteria, especially the longitudinal prognostic criteria, either to manic-depressive insanity or to dementia praecox (i.e. schizophrenia). However, mainly because of their good prognosis, the vast majority of Brief and Acute Psychoses were allocated by Kraepelin and his fellows to the manic-depressive insanity group (Maj, 1984).