# Article: Diagnosis/"Disease" model of symptoms



## Guest (Apr 17, 2005)

Below is an excerpt from a VERY LONG article in the Americal Journal of Psychiatry. I think it explains pretty well some of the problems inherent in trying to diagose a mental symptom - how/why it is more the CLUSTER of different symptoms that define the patient's problem, particular unique situation, etc. rather than "I HAVE this" or "I do not have THAT"

Mental symptoms are NOT analogous to physical diseases, and when we try to make that square peg fit into the round hole, we are really confusing things.

I know it's long and terribly convoluted, lol..but for those like me who enjoy this stuff, this is a very very interesting one.

*Distinguishing Between the Validity and Utility of Psychiatric Diagnoses 
Robert Kendell, M.D., and Assen Jablensky, M.D.
American Journal of Psychiatry, 2003*

??..[excerpted from the middle of the article- Janine] Borrowing terms from psychometric theory, psychiatrists have mainly been concerned with concurrent and predictive validity, partly because of their relevance to the issue of the validity of diagnoses. Certainly, the ability to predict outcome, both in the absence of treatment and in response to specific therapies, has always been a crucial function both of physicians and of their diagnoses. *Indeed, Goodwin and Guze went so far as to assert that "diagnosis is prognosis" and referred approvingly to P.D. Scott?s observation that "the follow up is the great exposer of truth....It is to the psychiatrist what the post-mortem is to the physician." *

* ?The Implicit ?Disease Entity? Assumption*

*Thoughtful clinicians have long been aware that diagnostic categories are simply concepts, justified only by whether they provide a useful framework for organizing and explaining the complexity of clinical experience in order to derive inferences about outcome and to guide decisions about treatment. Unfortunately, once a diagnostic concept such as schizophrenia or Gulf War syndrome has come into general use, it tends to become reified. That is, people too easily assume that it is an entity of some kind that can be invoked to explain the patient?s symptoms and whose validity need not be questioned*. Even though the authors of contemporary nomenclatures may be careful to point out that "there is no assumption that each category of mental disorder is a completely discrete entity with absolute boundaries dividing it from other mental disorders or from no mental disorder" (DSM-IV, p. xxii), the mere fact that a diagnostic concept is listed in an official nomenclature and provided with a precise, complex definition tends to encourage this insidious reification. 

The weakness of the validity criteria of both Robins and Guze and Kendler was that those criteria implicitly assumed that psychiatric disorders are discrete entities and that the role of validity criteria is to determine whether a putative disorder, such as "good-prognosis schizophrenia" or paranoia, is a valid entity in its own right or a mild form or variant of some other entity. The possibility that disorders might merge into one another with no natural boundary in between?what Sneath called a "point of rarity," but what is better regarded as a zone of rarity?was simply not considered. Robins and Guze commented, for example, that "the finding of an increased prevalence of the same disorder among the close relatives of the original patients strongly indicates that one is dealing with a valid entity".

In reality, such a finding is equally compatible with the existence of continuous variation. It seems that the possibility of an increased prevalence of more than one disorder in the patients? first-degree relatives had not occurred to Robins and Guze. In a similarly revealing comment, they wrote that "the failure to achieve 100 percent success in predicting outcome and the overlap in the results of the family studies indicate that the criteria used for the separation need further refinement." They did not consider that the results might have occurred because no natural boundary exists between good- and poor-prognosis cases, in which case the limitations they identified would have resisted all attempts at improvement based on refinement of the diagnostic criteria.

Robins and Guze?s classic paper was written at a time when it was widely assumed that schizophrenia and manic-depressive (bipolar) disorder were transmitted by single?or at the most two or three?genes and before publication of the first studies examining whether there were "*zones of rarity" between related syndromes. *The situation now is quite different. Several attempts have been made to demonstrate natural boundaries between related syndromes or between a common syndrome such as major depression and normality, either by locating a zone of rarity between them or by demonstrating a nonlinear relationship between the symptom profiles and a validating variable such as outcome or heritability . Most such attempts have ended in failure. Several general population surveys have also demonstrated that quite minor differences in the definition of individual syndromes such as major depression may result in large differences in recorded prevalence , again suggesting that the boundary identified by the definition does not correspond with a natural *zone of rarity*.

At the same time, research is increasingly supporting the view that many different genes contribute to the etiology of most of psychiatry?s major syndromes and that some of these genes are risk factors for what have until now been regarded as unrelated syndromes. Several other DSM/ICD disorders have been found to cluster among the relatives of individuals with schizophrenia, major depression, or bipolar affective disorder, and findings of such clusters have given rise to the concepts of "schizophrenia spectrum" and "affective spectrum" disorders. Increasing evidence also suggests that several genetic susceptibility loci may be common to two or more clinically distinct disorders. For example, three of the putative susceptibility loci associated with bipolar disorder (on chromosomes 13, 18, and 22) seem also to contribute to the risk of schizophrenia . In addition, the microdeletion in region q11 on chromosome 22, which underlies the velocardiofacial syndrome, appears to be associated with a higher incidence of mental retardation, schizophrenia, and bipolar affective disorder as well . Furthermore, the genetic basis of generalized anxiety disorder appears to be very similar to, if not indistinguishable from, that of major depression , and the genetic basis of schizophrenia seems to encompass a spectrum of other disorders, including schizotypal/paranoid personality disorder and even psychotic affective illness . It will not be surprising if in time such findings of overlapping genetic predisposition to seemingly unrelated disorders become the rule rather than the exception. It is equally likely that the same environmental factors contribute to the genesis of several different syndromes. Sexual or physical abuse and neglect in childhood, for example, seem to increase the risk of both anxiety and depression in adult life , and sexual abuse may increase the risk of bulimia nervosa and of alcohol and other substance dependence as well.

* Increasing Disenchantment with the ?Disease Entity? Assumption*

Although ubiquitous in both medical and lay discourse, the term "disease" has no unambiguous, generally accepted definition. However, as Scadding pointed out, most of those using this term "allow themselves the comfortable delusion that everyone knows what it means." Albert et al. catalogued six general views or concepts about "what types of conditions may be said to constitute a disease," ranging from nominalism and cultural-relativistic theories (i.e., something becomes a disease when a profession or society labels it as such) and social idealism (failure to attain a social ideal of perfect health) to culturally normative statistical concepts (deviation from statistically defined normality) and the "disease realism" view (objectively demonstrable departure from adaptive biological functioning). In adopting the last model as the one best suited to the present state of medicine, they emphasized that the clinical signs and symptoms do not constitute the disease and that it is not until causal mechanisms are clearly identified that "we can say we have ?really? discovered the disease"

Although each of these general concepts of disease has been used by psychiatry at some time, it is the "disease realism" model (in both its biological and psychodynamic versions) that has dominated the debate since the end of the 19th century. Kraepelin?a staunch "disease realist"?long believed that dementia praecox and manic-depressive insanity, defined by painstaking clinical observation of their symptoms and outcome, represented distinct species of brain disease whose causal mechanisms would ultimately be discovered by neuropathology, experimental psychology, and genetics. Eventually, however, he abandoned his assumption that these two disorders were discrete entities and proposed instead a model that was essentially dimensional. About the same time, Jaspers wrote that "the idea of the disease-entity is in truth an idea in Kant?s sense of the word: the concept of an objective which one cannot reach...but all the same it indicates the path for fruitful research and supplies a valid point of orientation for particular empirical investigations" (p. 569). He then added that, although "the idea of disease-entities has become a fruitful orientation for the investigations of special psychiatry...no actual disease-entities exist" (p. 570).

The relevance of this view to the present taxonomic debate in psychiatry is twofold. First, discrete disease entities and dimensions of continuous variation are not mutually exclusive means of conceptualizing psychiatric disorders; both are compatible with a threshold model of disease and may account for different or even overlapping segments of psychiatric morbidity. Second, the surface phenomena of psychiatric illness (i.e., the clustering of symptoms, signs, course, and outcome) provide no secure basis for deciding whether a diagnostic class or rubric is valid, in the sense of delineating a specific, necessary, and sufficient biological mechanism.

*Several well-informed commentators have produced evidence suggesting that there may be no natural boundary between recognized mental disorder and normality or health. Widiger and Clark suggested that variation in psychiatric symptoms may be better represented by "an ordered matrix of symptom-cluster dimensions" than by a set of discrete categories. *Cloninger stated firmly that "there is no empirical evidence" for "natural boundaries between major syndromes," that "no one has ever found a set of symptoms, signs, or tests that separate mental disorders fully into non-overlapping categories," and that "the categorical approach...is fundamentally flawed." Frustrated by the failure of two decades of laborious research to identify any of the genes underlying the major psychiatric syndromes, Ginsburg et al. complained that "current nosology, now embedded in DSM-IV...does not define phenotypes for genetic study."

Comorbidity poses a further problem that is becoming increasingly clamant as its full extent is revealed by community studies. As Sullivan and Kendler commented, the scale of the apparent comorbidity between major depression, various anxiety disorders, and addictive syndromes is "not consistent with the orthodox conceptualization of these psychiatric disorders as discrete nosological entities." The accumulation of such evidence and opinions led Allen Frances, the chairperson of the task force that produced DSM-IV, and Helen Egger to comment gloomily, but perhaps presciently, that "we are at the epicycle stage of psychiatry where astronomy was before Copernicus and biology before Darwin. Our inelegant and complex current descriptive system will undoubtedly be replaced by...simpler, more elegant models."

This disenchantment is understandable in the light of the failure of the revolutionary new nosology provided by DSM-III and its successors to lead to major insights into the etiology of any of the main syndromes. But disillusionment may not yet be justified. Although there is a growing assumption, at least within the research community, that most currently recognized psychiatric disorders are not disease entities, this belief has never been demonstrated, mainly because studies of the appropriate kind have rarely been mounted


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