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.
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.
Kraepelin also demonstrated specific patterns in the genetics of these disorders and specific and characteristic patterns in their course and outcome. Generally speaking, there tend to be more schizophrenics among the relatives of schizophrenic patients than in the general population, while manic-depression is more frequent in the relatives of manic-depressives.
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 signifing the irreversible mental decline). (It later became clear that dementia praecox did not necessarily lead to mental decline and so was renamed by Eugen Bleuler to correct the misnomer.)
Kraepelin postulated that there is a specific brain or other biological pathology underlying each of the major psychiatric disorders. As a colleague of Alois Alzheimer, and co-discoverer of Alzheimer's disease, it was his laboratory which discovered its pathologic basis. Kraepelin was confident that it would someday be possible to identify the pathologic basis of each of the major psychiatric disorders.
Kraepelin also dedicated much of his research to analyzing pedophilia. His motivation for this was due to the fact that he experienced occasional pedophilic urges.
Kraepelin's great contribution in discovering schizophrenia and manic-depression remains relatively unknown to the general public, and his work, which had neither the literary quality nor paradigmatic power of Freud's, is little read outside scholarly circles. Kraepelin's contributions were to a good extent marginalized throughout a good part of the twentieth century, during the success of Freudian etiological theories. However, his views now dominate psychiatric research and academic psychiatry, and today the published literature in the field of psychiatry is overwhelmingly biological in its orientation. His fundamental theories on the etiology and diagnosis of psychiatric disorders form the basis of all major diagnostic systems in use today, especially the American Psychiatric Association's DSM-IV and the World Health Organization's ICD system. In that sense, not only is Kraepelin's significance is historical but also contemporary scientific psychiatry is directly based on his findings and theories.
- Burgmair, Wolfgang & Eric J. Engstrom & Matthias Weber, et al., eds. Emil Kraepelin. 7 vols. Munich: belleville, 2000-2008.
- Vol. VII: Kraepelin in Munich, Teil II: 1914-1926 (2008, forthcoming)
- Vol. VI: Kraepelin in Munich, Teil I: 1903-1914 (2006), ISBN 3-933510-95-3
- Vol. V: Kraepelin in Heidelberg, 1891-1903 (2005), ISBN 3-933510-94-5
- Vol. IV: Kraepelin in Dorpat, 1886-1891 (2003), ISBN 3-933510-93-7
- Vol. III: Briefe I, 1868-1886 (2002), ISBN 3-933510-92-9
- Vol. II: Kriminologische und forensische Schriften: Werke und Briefe (2001), ISBN 3-933510-91-0
- Vol. I: Persönliches, Selbstzeugnisse (2000), ISBN 3-933510-90-2
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