Dementia praecox (a "premature dementia" or "precocious madness") refers to a chronic, deteriorating psychotic disorder characterized by rapid cognitive disintegration, usually beginning in the late teens or early adulthood. It is a term first used in 1891 in this Latin form by Arnold Pick (1851–1924), a professor of psychiatry at the German branch of Charles University in Prague. His brief clinical report described the case of a person with a psychotic disorder resembling hebephrenia (see below). It was popularized by German psychiatrist Emil Kraepelin (1856–1926) in 1893, 1896 and 1899 in his first detailed textbook descriptions of a condition that would eventually be reframed into a substantially different disease concept and relabeled as schizophrenia. Kraepelin, regarding the major psychoses as naturally occurring disease entities, reduced the complex psychiatric taxonomies of the nineteenth century by dividing them into two classes: manic depressive psychosis or dementia praecox. This division is commonly referred to as the Kraepelinian dichotomy and it has had a significant and fundamental impact on twentieth-century psychiatry, though has also been questioned.
The primary disturbance in dementia praecox was said to be not one of mood, but of thinking or cognition. Cognitive disintegration refers to a disruption in cognitive or mental functioning such as in attention, memory, and goal-directed behavior. Kraepelin contrasted this with manic-depressive psychosis, in which he included not just what would be termed bipolar disorder today but also other forms of mood disorder, including major depressive disorder. However, Kraepelin himself noted cases in between and eventually accepted that it was not possible to distinguish his categories on the basis of cross-sectional symptoms. Indeed, a mixed diagnosis of schizoaffective disorder has also developed.
From the outset, dementia praecox was viewed by Kraepelin as a progressively deteriorating disease from which no one recovered. The three terms that Kraepelin used to refer to the end state of the disease were "Verblödung" (deterioration), Schwachsinn (mental weakness) or Defekt (defect). Although "dementia" is part of the name of the disease, Kraepelin did not intend it to be similar to senile dementia and rarely used this term to refer to the end state of the disease. However, by 1913, and more explicitly by 1920, Kraepelin admitted that although there seemed to be a residual cognitive defect in most cases, the prognosis was not as uniformly dire as he had stated in the 1890s. Still, he regarded it as a specific disease concept that implied incurable, inexplicable madness.
Read more about Dementia Praecox: Kraepelin's Influence On The Next Century, From Dementia Praecox To Schizophrenia, Diagnostic Manuals, Conclusions