Mental and Behavioral Disorders Research Paper

Key requirements of diagnostic classifications systems in medicine are:

(a) reliability in terms of the consistency with which diagnostic classificatory decisions are made;

(b) validity in terms of agreement between basic research and clinical utility for intervention, for example;

(c) comprehensiveness in terms of coverage of all relevant disease phenomena across the age span;

(d) relevance for prognosis in terms of further course, remission, and relapse;

(e) utility for research in terms of the consistent and reliable collection of data to permit the generation and testing of hypotheses.

Since Hippocrates’ time, there have been numerous attempts to classify psychiatric diseases according to a few major classes. The systematic and scientifically based search for such classification systems is, however, a relative recent phenomenon. Kraepelin’s influential experimental-based distinctions and various nosological modeling exercises that separated mood disorders from dementia praecox (later known as schizophrenia), along with the increasing availability of research methods and competing concepts, gave rise to the development of numerous phenomenological classification attempts in the first half of the twentieth century. Most of these systems of thought are, however, based on dubious or speculative etiological assumptions and use a wide range of variably defined cognitive, affective, and behavioral signs and symptoms along with aspects of course, outcome, and intensity as the key defining characteristics of mental disorders. Despite the fact that almost all of these systems focused on only a few forms of mental disorders, there was little agreement among these different classification systems in terms of principles and common concepts. Consequently, until 1950, there were hundreds of various psychiatric classification systems worldwide, which did not comply with the key requirements of classification systems in terms of comprehensiveness, reliability, validity, and utility for research and intervention (Blashfield 1984).

This heterogeneity reflected, on the one hand, the multifaceted presentations of mental disorders with regard to biological, social, and psychological manifestations and, on the other, the poor state of scientific research and knowledge concerning the nature and the causes of mental disorders until the mid-twentieth century. A further obstacle is that, for modern medicine, the ideal and ultimate goal of diagnostic classification systems is a ‘nosological’ classification. The term nosology refers to an integrative and comprehensive derivation of models of diseases within the framework of a logical order, according to specified ‘natural criteria’ that are based not only on shared similarities and differences of all objectively given logical phenomena, but also on their respective etiological and pathogenic factors (e.g., genetic, neurobiological, psychological) proven to be of relevance in experimental and empirical research. For mental disorders, the derivation of such logical, natural, and comprehensive systems of illnesses seems premature. Therefore, even now, current classification systems for mental and behavioral disorders (previously called psychiatric classification systems) remain mainly descriptive and phenomenological. Thus, strictly speaking, they have to be considered as typologies.

Although recent research progress in neurobiology and psychology have led to increasing agreement about more adequate classification principles, it seems unlikely that there will ever be absolute and infallibly perfect criteria for mental disorders as well as a true classification of diseases: first, because of the complexity of what could be summarized under mental and behavioral disorders; second, because of the dependence of progress in scientific knowledge about the causes, nature, course, and outcome of mental disorders. Furthermore, the term mental disorders implies a distinction between ‘mental’ disorders and ‘physical’ disorders, which is, according to our current knowledge, a reductionist anachronism of mind-body dualism. There is compelling scientific evidence that there is a lot that is physical in mental disorders, as well as much that is mental in physical disorders. It seems fair to emphasize that the problem raised by the term mental disorders has been much clearer than any solution; thus the term unfortunately persists in the titles of all classificatory systems because no appropriate substitute has yet been found.

In light of this continuing dilemma, it was agreed in the 1980s and 1990s to use descriptive, phenomenological, psychopathological classification systems of mental and behavioral disorders, instead of nosological ‘psychiatric’ systems. Examples of up-to-date nomenclatures and respective classifications for mental and behavioral disorders that will be highlighted here are chapter F (Mental and Behavioural Disorders) of the tenth revision of the International Classification of Diseases (ICD-10, WHO 1991), as well as the Diagnostic and Statistical Manual of Mental Disorders, 3rd and 4th revisions (DSM-III and DSM-IV, American Psychiatric Association 1980, 1994). As DSM-IV is the major diagnostic classification system used in scientific research around the world, this overview focuses primarily on DSM-IV because of its greater stringency and scientific utility.

2. Towards a Systematic and Comprehensive International Classification of Mental Disorders

The 8th revision of the WHO International Classification of Diseases, injuries and causes of death (ICD- 8, WHO 1971) in the 1960s signaled the beginning of systematic efforts at an international level to make a serious attempt to develop a unified system of classification of mental disorders. However, despite improvements brought about by this attempt and its 9th revision (ICD-9, 1978) with regard to agreement about the core spectrum of classes of relevant disorders and increased comprehensiveness, the diagnostic guidelines remained limited to narrative descriptions that provided neither a well-defined nomenclature and glossary nor specific diagnostic criteria. Although ICD-8 9 presented for the first time a more comprehensive and systematic tabulation of mental disorders, they relied almost exclusively on clinical judgment and its application by psychiatrists. Therefore, they were appropriately labeled Psychiatric Classification Systems. Due to ICD-8 9’s narrative nature, which did not include explicit criteria and rules and which was strongly bound to so-called ‘clinical judgments by psychiatrists,’ diagnosing of mental disorders was more an art than a science, plagued by unreliability and lack of validity and research and clinical utility.

With the increasing interest in systematic basic and applied research on mental disorders and the need for cross-national multicenter studies, it became quickly evident that even broad ICD diagnoses such as anxiety neurosis, depressive neurosis, and schizophrenia could not be compared between countries or even between various psychiatric schools within any given country. Another shortcoming of these systems was that they were not uniformly accepted by other core scientific disciplines such as psychology, neuropharmacology, and other allied disciplines that had gained greater influence in mental disorders research and intervention since the 1960s.

The increasing degree of dissatisfaction in psychiatry, clinical psychology, and the allied disciplines stimulated greater opposition and a search for alternative approaches: (a) antipsychiatric movements and sociological alternatives that defied the usefulness of any psychiatric diagnoses; (b) unitarian positions that classified mental disorders by degree of disturbance of key functions; and (c) a ‘diagnostic nihilism’ that was especially pronounced in both clinical psychology and psychoanalytical schools of thought. The latter, in particular, emphasized the need for alternative classification systems built, however, on yet partly unproven etiological and therapeutic models that seemed to promise at least greater utility for therapeutic decisions.

At the same time psychology, and clinical psychology in particular, started to provide new, promising methods and behavioral, psychophysiological, and cognitive models based on experimental research. Increasingly psychometric and psychopathometric studies attracted attention, especially in the context of new behavioral and pharmacological treatments that became available for many mental disorders. Empirical psychological methods, such as the use of

psychometric instruments (i.e., self-report and clinician-rated) based on test theory and key psychometric properties of objectivity, reliability, and validity, were used in more detailed and reliable assessments and descriptions of observable manifestations of acute and chronic psychopathological phenomena. These developments offered various rational ways of improving the diagnostic classification process in terms of reliability, as a prerequisite for improved future validity (Matarazzo 1983), and were also instrumental for subsequent progress in neurobiological, genetic, and psychopharmacological research in mental disorders.

3. Explicit Criteria and Operationalized Diagnoses within a Comprehensive Multi-axial Classification System

The advent of DSM-III (American Psychiatric Association 1980) and their fourth revision DSM-IV (American Psychiatric Association 1994) marked the beginning of the contemporary era in the diagnosis and classification of mental disorders. More consistent with the preceding psychometric studies and linked validation work, every diagnostic category—from infancy to old age—was now given an operational definition, strictly descriptive and as ‘neutral’ as possible. Necessary symptoms and phenomena were specified, along with rules on how to calculate a diagnostic decision based on signs, symptoms, and their duration; syndromes and diagnostic exclusions were also included (Table 1).

This ‘atheoretical’ (in the sense of deleting ‘unproven’ nosologies) and descriptive approach substantially increased the diagnostic reliability of the assessment of psychopathology and the process of making diagnostic decisions of mental disorders (Wittchen and Lachner 1996). Furthermore, due to the empirical nature of this approach, subsequent revisions and improvements of the reliability, validity, and clinical and research utility of this classification system could begin to be systematically related to empirical evidence derived from the application of these strict criteria. Although one needs to acknowledge that not all of these criteria have yet been fully validated by data about important correlates, clinical course and outcome, family history, and treatment response, they are at least partially based on empirical studies. These DSM criteria could be regarded as helpful intermediate steps which we can expect will lead to further refinements following further studies.

3.1 Operational Diagnostic Criteria

The DSM-III IV approach is superior to previous classification systems in terms of observability (emphasis on explicit behavioral symptoms), reliability (in terms of agreement among clinicians), validity (in terms of agreement with other criteria), feasibility (ease of administration), coverage (covering all disorders of clinical significance in the mental health system), and age sensitivity (from infancy to old age). It also acknowledges the continuous need to increase further the observability, reliability, validity, feasibility, coverage, and age sensitivity of the system, as well as to modify the specific diagnostic categories in light of empirical advances in mental health research.

3.2 Definition of Mental Disorder

Although there is still no perfect definition or precise boundaries for what constitutes a mental disorder (similar to the concepts of somatic disorder and physical health), DSM-III has at least attempted to specify what constitutes a mental disorder:

Each mental disorder if conceptualized as a clinically significant behavioral or psychological syndrome or pattern that occurs in a person and thus is associated with present distress (a painful symptom) or disability (impairment in one or more important areas of functioning) or with a significantly increased risk of suffering death, pain, disability or an important loss of freedom. In addition, this syndrome or pattern must not be merely an expectable response to a particular event, e.g., the death of a loved one. Whatever its original cause, it must currently be considered a manifestation of a behavioral, psychological or biological dysfunction in the person. Neither deviant behavior (political, religious or sexual) nor conflicts that are primarily between the individual and the society are mental disorders unless the deviance or conflict is a symptom of dysfunction in the person as described above. There is no assumption that each mental disorder is a discrete entity with sharp boundaries (discontinuity between it) and other mental disorders or between it or no mental disorder. (American Psychiatric Association 1994)

3.3 Multi-axial Evaluation

There is increasing evidence that the complexity of mental and behavioral disorders cannot be described adequately by focusing merely on psychiatric symptoms. Therefore, in accordance with previous studies, DSM suggested classifying patients with regard to phenomena on five axes (Table 1). In its entirety, the multiaxial system provides a biopsychosocial approach to mental disorders and their assessment.

3.4 Descriptive Approach

The etiology or pathophysiological processes are known in detail for only a few mental disorders, such as for so called ‘organic mental disorders’ where organic (biological) factors have been proven to be necessary for the development and maintenance of the respective disorder. For most of the other disorders, however, the etiology is unknown, beyond the finding that, for all disorders, a complex vulnerability-stress model seems to be the most adequate. Although many theories have been advanced to explain core-psychopathological processes for some disorders, the explanations at this point remain unsatisfactory and thus do not provide a firm basis for classification. Therefore, current classification systems for mental disorders are largely atheoretical with regard to the specific etiology or pathophysiological processes. The current system is descriptive, referring to the fact that the definitions of disorders are generally limited to descriptions of the clinical features of the disorders, consisting of easily identifiable behavior signs or symptoms, such as pathological anxiety reactions (i.e., panic attack), mood disturbances, and certain psychotic symptoms that require a minimal amount of inference on the part of the observer (Table 2).

The descriptive approach is also used to group mental disorders into diagnostic classes by the use of operationalized definitions which specify in a prototypical way all the mandatory symptoms and additional criteria used for the diagnosis of a disorder. All of the disorders with a known etiology of pathophysiology are grouped into classes on the basis of shared clinical features. Others are classified according to a key syndrome, such as the presence of anxiety reactions and avoidance behavior in anxiety disorders.

3.5 Systematic Description

Beyond the operationalization of diagnosis, the descriptions of disorders are more comprehensively described in terms of essential features, associated features, age-of-onset, course impairment complications, predisposing factors, prevalence, familial patterns, and differential diagnosis. This provides a better understanding of the disorder itself and has been shown to reduce the degree of misinterpretation of the explicit diagnostic criteria for symptoms, syndromes, and diagnosis by users in research and clinical settings.

3.6 Comorbidity

DSM’s goal of a broader descriptive and atheoretical psychopathological classification system has necessarily led to a considerable increase in the number of diagnoses covered and in a substantially higher rate of patients with multiple diagnoses. The occurrence of more than one specific mental disorder in a person has been labeled ‘comorbidity.’ Unlike previous systems, which used questionable hierarchical rules to reduce the substantial degree of comorbidity in an attempt to arrive at a core or main diagnosis, DSM-IV encourages the assignment of multiple diagnoses, both cross-sectionally as well as longitudinally (over the person’s life) for various reasons:

(a) to increase the reliability of diagnostic assessments,

(b) to ensure that empirical psychopathological data are collected to better understand the boundaries of mental disorders and their inter-relationships,

(c) ultimately to arrive at a crisper and scientifically sound classification of mental disorders based on core psychopathological processes, and

(d) to enhance the system’s utility in terms of clinical and basic research purposes (Wittchen and Lachner 1996).

Studies such as the US National Comorbidity Survey (Kessler et al. 1994) have demonstrated that comorbidity is a basic characteristic of all mental disorders, caused by neither a methodological artifact nor a help-seeking bias, and that comorbidity might have diagnosis-specific implications for severity, impairment, course and outcome (Wittchen 1996). There is also some evidence of the existence of broad, higherorder factors of phenotypic psychopathology that, in the future, might actually allow the organization of common psychopathological variables in terms of common genetic, neurobiological, and psychological factors.

4. The Relationship of the ICD-10 and the DSMIV Classification of Mental Disorders

Although the 1980s and 1990s have seen an increasing degree of agreement about the major classes of mental and behavioral disorders along with the common language and nomenclature, it is important to recognize that there are still two major international classification systems in use, the ICD-10 and DSM-IV. The wide acceptance with increased clinical utility of the DSM approach prompted the World Health Organization in the early 1990s to develop, jointly with the DSM task forces, a congruent and quite similar system of more explicit diagnostic classification organized in the same way as DSM, but for worldwide use. Nevertheless, due to the fact that the ICD has been adopted by all countries and health care systems, some minor differences with regard to the organization and the scope of diagnoses covered between ICD-10 and DSM-IV need to be highlighted.

(a) ICD-10 has been produced by the World Health Organization in different user versions. In addition to the clinical diagnostic guidelines for clinical use, WHO has published separate versions for research and for the purposes of administration, primary care, and disability.

(b) DSM-IV operationalizes mental disorders within its diagnostic manual with emphasis on associated psychosocial dysfunctions. ICD-10, on the other hand, tends to shift the assessment of psychosocial impairments and disabilities towards different axes for classification (ICD-10 Classification of Impairments, Disabilities, and Handicaps) as part of the ICD-10 multi-axial system.

(c) DSM-IV is characterized by clearer and explicit structuring in defining mental disorders, whereas ICD- 10 tends to be more general and unspecific, thus retaining, at least partially, the narrative guidelines format.

(d) Furthermore, there are some conceptual differences in the definition of some mental disorders such as schizophrenia and other psychotic disorders as well as anxiety disorder that might lead to some diagnostic differences, despite the same presentation of the patient when coding the more subtle distinctions of diagnostic classes (e.g., panic and agoraphobia, personality disorder).

Yet, it needs to be acknowledged that the process of coordination between the two partly competing systems has been taken seriously in that all DSM diagnoses covered in the 4th revision also match comparable ICD-10 F-codes, resulting in a high degree of convergence.

5. Conceptual Changes

Making our current classification systems ICD-10 and DSM-IV comprehensive, atheoretical, and descriptive implies a number of conceptual changes, in comparison to their predecessors. These changes do not only refer to the increased number of diagnoses along with the emphasis on diagnosing comorbid conditions whenever appropriate, they also influence our understanding of specific types of disorders.

5.1 Schizophrenia and Psychotic Disorders

To match new scientific evidence, demonstrating significantly different patterns of course and outcome and risk factors, as well as to increase reliability, both systems, ICD-10 and DSM-IV, have differentiated considerably the classification of schizophrenia and other psychotic disorders. By using stricter time and symptom criteria, the concept of schizophrenia is narrowed in favor of a better delineation from other psychotic disorders, as well as from psychotic symptoms occurring in the course of affective disorders. These changes built on various studies that have highlighted differences in prognosis and treatment response of psychotic disorders and also aim at the reduction of a possible stigmatizing and negative effect of false positive diagnosis of schizophrenia.

5.2 The Departure from the Concept of Neurosis

In previous systems, the so-called ‘neurotic disorders’ comprised a large heterogeneous group of manifestations of anxiety (i.e., anxiety neurosis, phobic neuroses), depressive (i.e., depressive neurosis), somatoform conditions (hysterical neurosis), and personality disorders (characterological neurosis). However, the common etiological denominator ‘neurosis’ has never been proven, nor could the disorders be reliably diagnosed. Therefore, the broad concept of neurosis was discarded in favor of a disorder-specific classification of numerous types of specific conditions, for each of which firmer scientific evidence was available. This change resulted in a considerable increase of diagnoses; for example, panic disorder and generalized anxiety disorder largely replaced former anxiety neurosis; depressive neurosis was replaced by the descriptive term major depression or dysthymia; phobic neurosis was broken down into agoraphobia, social, and various forms of specific phobias. Furthermore, this departure from neurosis allowed for a more clear-cut differentiation of affective (mood) disorders from anxiety disorders and a departure from the controversial and unproven differentiation of socalled endogenous (caused by biological factors) and neurotic (reactive and neurotic-developmental etiology) depressions.

5.3 Addictive Disorder

Whereas in the past ICD-8 and -9 used a fairly generalized and poorly defined concept of addiction, ICD-10 and DSM-IV built on a substance-specific syndromatic classification of ‘abuse and dependence,’ supplemented by numerous substance-related specific problems (i.e., intoxication syndrome), frequently seen and underdiagnosed in health care settings. The differentiation of substance-specific criteria accounts for research findings that have highlighted the substance-specific risk factors and correlates and treatment implications on the one hand, and the need for a reliable assessment of dependence syndromes on the other.

These examples highlight that the modern classification systems for mental and behavioral disorders have brought the field much closer to the paradigms and procedures of basic and clinical research—for example, neurobiology, neuropharmacology, and clinical psychology. Each of these core disciplines can now build in research on the same uniform and reliable criteria as they are used in clinical research and practice. This achievement has, for the first time, opened the door to subsequent empirically based revisions and changes in future systems.

6. Improving the Diagnostic Process and Diagnostic Instruments

Assigning diagnoses of mental disorders according to the current classification systems can be described as a complex process in which a clinician makes inferences about the patient’s ‘true’ health state, using various measures ranging from structured assessments about an individual’s past and current physical, mental, and social history to laboratory tests. Within this framework, diagnostic decision theories (Fig. 1) continue to assist in identifying the key aspects involved in making inferences about the ‘objective’ state of the patient, by using various sources of information of varying degrees of reliability and validity, and taking into account the clinical evaluation process needed to interpret these findings. Such investigations are essential in improving classification systems of mental disorders, because they largely depend on the verbal interaction between a diagnostician and the patient. Building on the current state of knowledge about the nature and course of mental disorders, the key problematic issues of diagnostic classification in mental disorders have become apparent:

(a) For mental disorders, reliable and objective laboratory or neuropsychological markers are not currently available; therefore, improved classification systems should focus on clearer guidelines of assessment for key psychopathological symptoms in terms of their subjective (patient self-report) and clinician-observed (clinical rating) aspects.

(b) Mental disorders vary in terms of onset, risk factors, course, duration, severity, and associated disability. Therefore, it is necessary to establish clear criteria regarding symptoms and phenomena for the diagnosis of specific disorders, along with clear criteria regarding duration, onset, severity, and other associated behavioral aspects.

(c) Many psychopathological terms used for classification purposes in the past stem from various theoretical, yet unproven and untested, hypotheses referring to various theoretical schools of thought for mental disorders. Examples of such ambiguous terms that are neither shared by all users nor supported by experimental studies are diagnostic terms, such as ‘endogenous depression’ and ‘neurosis,’ and psychopathological symptoms, such as ‘frustration tolerance,’ all of which are only vaguely described and not consistently assessable. Therefore, there is the need for well-defined psychopathological terms that can be evaluated with high reliability by all mental health professionals, irrespective of their theoretical orientation.

Referring to the model of the diagnostic process that structured the diagnostic process for mental disorders in a systematic way (Fig. 2), numerous empirical studies have resulted in specific suggestions regarding how to improve its consistency and reliability (Wittchen and Lachner 1986). Ideally, this diagnostic process starts with the reliable assessment of all relevant cognitive, affective, behavioral as well as biological, psychosocial, and social-interactive phenomena by assessing systematically all complaints, signs and symptoms of a patient. In agreement with the medical decision process, the core features of these manifestations can be labeled symptoms. According to certain rules, symptoms can be further translated into syndromes, characterized by a systematic association of frequent symptom configurations. Then, according to further clinical-nosological rules and hierarchical decisions, symptoms can be translated to diagnoses of mental disorders.

The extensive psychometric and methodological work in this domain resulted in subsequent and still ongoing attempts to improve not only the reliability of the diagnostic process (by specifying core symptoms and syndromes in DSM-III, IV and the ICD-10) and their systematic validation, in terms of agreement with other basic and clinical markers (Robins and Barrett 1989), but also their translation into diagnostic assessment instruments for research and clinical use. Research in diagnostic assessment has high priority for the developers of ICD-10 and DSM-IV. In fact, the development of structured diagnostic interviews and their more radical next step, namely, the development of fully diagnostic standardized diagnostic interviews (see American Psychiatric Association 2000), has been made possible only by the existence of explicit descriptive diagnostic criteria and the specification of diagnostic algorithms for hundreds of specified diagnoses of mental disorders, and the intimate interaction between both the developers and users of the instruments, as well as developers of the classification system. It is now routine in basic and clinical research to require the use of comprehensive and systematic interviews that call for a standardized review of all explicit criteria, explicit wording to initiate more or less strictly defined probing of specific symptoms, and consensus standards to define thresholds for dichotomous symptom and disorders classifications of openended responses (Wittchen 1994). With careful training and close monitoring of diagnostic ratings, it is now possible to obtain good inter-rater agreement when using diagnostic interviews.

There are several reasons for standardizing the diagnostic process and the use of instruments: (a) Learning the new classifications systems: Unlike the past when clinicians and researchers had to deal only with a handful of diagnoses, they now have to diagnose hundreds of diagnoses for mental disorders, each with its unique set of criteria. It is hard to see how they are able to use such complex classification systems appropriately and reliably without the use of diagnostic tools that guide them through the system. (b) Quality assurance: diagnosing mental disorders requires a comprehensive cross-sectional and longitudinal assessment of the patient’s symptomatology along with the need to make subtle distinctions with regard to key phenomena, time, and severity criteria. Because for the vast majority of mental disorders, this process relies almost entirely on subjective-verbal interactions between the patient and the diagnostican, it is unlikely that ‘clinical judgment’ within an unstructured clinical assessment alone will result in adequate decisionmaking. As the 1980s and 1990s have witnessed a tremendous increase in effective behavioral and medication treatments for specific disorders assessed with such instruments, reliable and valid diagnostic interviews should be made a standard requirement for routine care, as well as to ensure proper diagnostic standards and appropriate treatment allocation.

7. Future Perspectives

7.1 Diagnostic Assessment and the ‘Science of Self-report’

Beyond the continued need for refinement of the diagnostic process and the improvement of diagnostic instruments, classification systems for mental disorders have also started to profit from an increasingly closer collaboration of developers of diagnostic interviews with cognitive psychologists and survey methodologists (Stone et al. 2000). Diagnostic interviewing for classificatory purposes is a highly complex process between a patient and a diagnostician. Asking the right question and making sure that the patient understands the question is a challenge for the diagnostician. Challenges for the patient include: understanding the task (thoughtful and honest responding), being willing to carry out the task (motivation), and being able to carry out the task (dealing with questions that might be ambiguous or exceed the limits of memory or cognition). Cognitive psychologists have developed a number of strategies to deal with such problems, few of which are currently systematically applied in clinical interviews. ‘Think aloud’ experiments and cognitive debriefing interviews are two examples of effective methods of detecting and correcting the problem of misunderstanding and other limitations of diagnostic interviews. It can be expected that a more systematic application of such clinical validation strategies will considerably lessen diagnostic assessment difficulties and ultimately result in improved classification rules and definitions.

7.2 Biological Tests and Correlates

Currently no biological findings are available that can be used as reliable diagnostic markers for mental disorders, nor are discoveries in sight that might provide an immediately available, firmer, and more objective basis for classifying mental disorders. However, referring to the tremendous progress in innovative neurobiological methods, there are some potential areas from which such markers, at least for some diagnoses, might be derived.

Among neuroendocrine tests the hypothalamicpituitary-adrenocortical axis has received the most attention. The Dexamethasone Suppression test (DST) was the first and most studied marker in research of depressive disorders (Carroll et al. 1986). Based on the observation that depressed patients fail to suppress plasma cortisol, it was believed that a positive DST might be a specific laboratory test for severe forms of depression. Although subsequent studies confirmed the high specificity versus normal and non-psychiatric controls, there was no specificity in comparison to other mental disorders or healthy controls who had experienced a recent stressful life event. Similar specificity problems were also found for other neuroendocrine tests, such as the adrenocorticotrophic hormone (ACTH) response to corticotropin releasing factor (CRF) and growth hormone releasing hormone (GHRH), as well as sleep and neuroimaging studies (Nemeroff 1996, Holsboer 1993). It is not entirely clear at this point to what degree the partly disappointing findings of such methods for diagnostic purposes are due to the fact that our currently phenomenological classifications may be inadequate targets for such experimental laboratory marker technologies. Yet, such findings as those emerging from molecular biology, functional brain imaging and genetic studies have and will considerably advance our basic knowledge about the complex functional pathways of mental functioning and mental disorders and remain key targets for improved future classification systems.

8. Conclusion

The past two decades have witnessed tremendous advances in the classification of mental and behavioral disorders with regard to increased reliability, validity, clinical and research utility, comprehensiveness, and improved communication. The current available systems, however, are far from being satisfactory. More research is clearly needed not only to improve further the reliability of explicit criteria and to clarify the boundaries of disorders, but, in particular, to explain more effectively the complex etiology and pathogenesis of mental disorders on neurobiological, psychological, and social-behavioral levels. Such research will result, hopefully, in the identification of common and disorder-specific core psychopathological processes that might provide more valid and comprehensive criteria for a sharper and more satisfactory classification system.

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