Editing Emil Kraepelin (section)

=== Psychosis and mood ===
Kraepelin is specifically credited with the classification of what was previously considered to be a [[Unitary psychosis|unitary concept of psychosis]], into two distinct forms (known as the [[Kraepelinian dichotomy]]):

* [[Bipolar disorder|manic depression]] (although commonly presented as synonym with bipolar disorder that is inaccurate; manic depressive illness encompasses a broader spectrum of mood disorders such as [[bipolar disorder]] and [[clinical depression|recurrent major depression]].<ref>{{cite journal | vauthors = Teodoro T, Durval R | title = Emil Kraepelin's taxonomic unitary view of manic-depressive insanity in the 21st century: the never-ending diagnostic conundrum of bipolar depression | journal = CNS Spectrums | date = October 2022 | volume = 28 | issue = 4 | pages = 389–390 | pmid = 36210529 | doi = 10.1017/s109285292200102x| s2cid = 252779392 | doi-access = free }}</ref>
* [[dementia praecox]].

Drawing on his long-term research, and using the criteria of course, outcome and [[prognosis]], he developed the concept of [[dementia praecox]], which he defined as the "sub-acute development of a peculiar simple condition of mental weakness occurring at a youthful age".  When he first introduced this concept as a diagnostic entity in the fourth German edition of his ''Lehrbuch der Psychiatrie'' in 1893, it was placed among the degenerative disorders alongside, but separate from, [[catatonia]] and [[dementia paranoides]]. At that time, the concept corresponded by and large with [[Ewald Hecker]]'s [[hebephrenia]]. In the sixth edition of the ''Lehrbuch'' in 1899 all three of these clinical types are treated as different expressions of one disease, dementia praecox.<ref>{{cite web|last=Yuhas|first=Daisy|title=Throughout History, Defining Schizophrenia Has Remained a Challenge (Timeline)|date=March 2013 |url=http://www.scientificamerican.com/article.cfm?id=throughout-history-defining-schizophrenia-has-remained-challenge|publisher=Scientific American Mind (March 2013)|access-date=2 March 2013}}.</ref>

One of the cardinal principles of his method was the recognition that any given symptom may appear in virtually any one of these disorders; e.g., there is almost no single symptom occurring in dementia praecox which cannot sometimes be found in manic depression. What distinguishes each disease symptomatically (as opposed to the underlying [[pathology]]) is not any particular ([[pathognomonic]]) symptom or symptoms, but a specific pattern of symptoms. In the absence of a direct physiological or genetic test or marker for each disease, it is only possible to distinguish them by their specific pattern of symptoms. Thus, Kraepelin's system is a method for pattern recognition, not grouping by common symptoms.

It has been claimed that Kraepelin also demonstrated specific patterns in the genetics of these disorders and patterns in their course and outcome,<ref>{{cite journal|last1=Ebert|first1=Andreas|title=Emil Kraepelin: A pioneer of scientific understanding of psychiatry and psychopharmacology|journal=Indian Journal of Psychiatry|pmc=2927892|pmid=20838510|doi=10.4103/0019-5545.64591|volume=52|issue=2|pages=191–2|year=2010 |doi-access=free }}</ref> but no specific [[biomarkers]] have yet been identified. Generally speaking, there tend to be more people with schizophrenia among the relatives of schizophrenic patients than in the general population, while manic depression is more frequent in the relatives of manic depressives. Though, of course, this does not demonstrate genetic linkage, as this might be a [[social|socio]]-[[Environmental psychology|environmental]] factor as well.

He also reported a pattern to the course and outcome of these conditions. Kraepelin believed that schizophrenia had a deteriorating course in which mental function continuously (although perhaps erratically) declines, while manic-depressive patients experienced a course of illness which was intermittent, where patients were relatively symptom-free during the intervals which separate acute episodes. This led Kraepelin to name what we now know as schizophrenia, dementia praecox (the [[dementia]] part signifying the irreversible mental decline). It later became clear that dementia praecox did not necessarily lead to mental decline and was thus renamed [[schizophrenia]] by [[Eugen Bleuler]] to correct Kraepelin's misnomer.

In addition, as Kraepelin accepted in 1920, "It is becoming increasingly obvious that we cannot satisfactorily distinguish these two diseases"; however, he maintained that "On the one hand we find those patients with irreversible dementia and severe cortical lesions. On the other are those patients whose personality remains intact".<ref>{{cite journal |vauthors=Berrios GE, Luque R, Villagran JM| year = 2003 | title = Schizophrenia: a conceptual history | url = http://www.ijpsy.com/volumen3/num2/60/schizophrenia-a-conceptual-history-esquizofrenia-EN.pdf | journal = International Journal of Psychology and Psychological Therapy | volume = 3 | issue = 2| pages = 111–140 }}</ref> Nevertheless, overlap between the diagnoses and neurological abnormalities (when found) have continued, and in fact a diagnostic category of [[schizoaffective disorder]] would be brought in to cover the intermediate cases.

Kraepelin devoted very few pages to his speculations about the etiology of his two major insanities, dementia praecox and manic-depressive insanity. However, from 1896 to his death in 1926 he held to the speculation that these insanities (particularly dementia praecox) would one day probably be found to be caused by a gradual systemic or "whole body" disease process, probably [[metabolic]], which affected many of the organs and nerves in the body but affected the brain in a final, decisive cascade.<ref>{{cite magazine|last=Noll|first=Richard|title=Whole Body Madness|url=http://www.psychiatrictimes.com/display/article/10168/2104852|magazine=Psychiatric Times|access-date=26 September 2012}}.</ref>