Classification Categories or continuua

We have in front of us a fruit called psychosis, and we don't know whether it's a citrus that will divide itself into separable sections or an apple that we must divide along arbitrary lines.

Belmaker and Van Praag (1980)

Bipolar affective disorder and schizophrenia constitute the twin pillars of classically defined psychosis. As Goodwin and Jamison (1990) point out, Kraepelin's (somewhat unintentional) legacy has divided psychotic illness into two entities, schizophrenia and manic depression. This can leave many patients in a diagnostic no man's land. Kendler (1986) has stated that "no area in psychiatric nosology has been as controversial". This controversy has formed the scaffolding for contemporary classification. However, excessive reliance on presenting symptoms and narrative and too little on the history of patients and their families can lead to undue reliance on one set of diagnostic rules at the expense of the true picture. Argument about the validity of the dichotomous classification of the major psychoses has been in progress for the last century, beginning soon after Kraepelin (1896) described his classification of dementia praecox and manic-depressive insanity in the fifth edition of his textbook.

The basic concept behind the classification of psychosis is that of the nosological entity (Jablensky, 1999), which has remained unchanged since formulated by Kahlbaum (1874); that is, a close correspondence between clinical symptoms, course and outcome, cerebral pathology and aetiology as the criteria for correlated clinical states constituting a "natural disease entity".

The resulting construction of the clinical entities of dementia praecox and manic-depressive illness from previously chaotic or arbitrarily subdivided clinical material represented an immense step forward (Jablensky, 1999). However, no neuropathological

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validation of these entities has been forthcoming, and the validating criteria have been restricted to:

(1) internal cohesion of the clinical picture

(2) course and outcome.

Kraepelin's manic-depressive insanity was a broader group than the modern concept of bipolar disorder, and the dementia praecox was narrower than ICD-10 or DSM-IV schizophrenia. This was reflected in the relative frequencies of the two diagnoses in Kraepelin's Munich University Clinic; manic-depressive illness accounted for 18.6% but dementia praecox for only 7.3% of all admissions in 1908 (Jablensky et al., 1993). These figures are substantially different from the typical annual admission rates expected in the contemporary setting, which would not record twice the number of manic-depressive as schizophrenic admissions.

Using the Present State Examination and CATEGO (Wing et al., 1973), Jablensky (1999) recoded Kraepelin's original case summaries of 53 cases of dementia praecox and 134 cases of manic-depression recognized in 1908. The overall concordance between Kraepelin's original diagnoses and the CATEGO was 80.2%. The coded raw data were applied to an independent taxonomic method, grade of membership analysis (Woodbury & Manton, 1982), to obtain a statistical grouping of clinical disorders and patients that could be compared with Kraepelin's original classification (Jablensky & Woodbury, 1995). The methods resulted in three groups of disorder clearly corresponding to bipolar affective disorder, unipolar depression, and dementia praecox. There was significant overlap between dementia praecox and bipolar disorder, with 19% of dementia praecox cases having secondary membership in the bipolar group and 17% vice versa. These results suggest a respectable level of concurrence between Kraepelin's typology of the psychoses and the clinical data on which it was based.

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