DSM-IV-TR, our current diagnostic classification system of psychiatric disorders, follows the diagnostic paradigm first established by DSM-III in 1980. Acknowledging the field’s ignorance about the underlying etiology and pathophysiology of mental disorders, DSM-III eschewed basing the structure of the classification and definition of disorders on unproven hypotheses about the causes of psychiatric disorders in favor of an “atheoretical” approach in which disorders were defined by their presenting symptoms.1 This reliance on purely descriptive operationalized definitions resulted in the establishment of a widely accepted reliable diagnostic system that has enhanced communication among mental health care professionals and greatly facilitated psychiatric research.
Critics of DSM-IV have justifiably been frustrated with the superficial nature of this descriptive approach. Paul McHugh,2 in a 2005 JAMA editorial, complained that “because the manual fails to identify what underlies the symptomatic expression of a condition, it cannot suggest intelligible principles relating one disorder to another or illuminate why certain of them bunch together. For these reasons, faith in the criterion method has gradually faltered.” It has always been understood that the descriptive approach adopted by DSM will eventually be replaced by a classification informed by an understanding of etiology, which would put psychiatry in line with much of the rest of medicine. Given that DSM-V is slated for publication in 2012, has the time finally arrived for an etiologically based classification, or, falling short of those aspirations, at least one that includes objective laboratory tests as part of its diagnostic definitions?
Given the enormous advances in imaging technology and molecular genetics over the past 15 years, one might assume that such an approach is finally within our reach. In fact, when Allen Frances and I wrote the DSM-IV Guidebook, given the explosion in new technologies available in the early 1990s, we were very optimistic that by the time DSM-V came out (which we envisioned would be sometime around 2007), it would include at least some biologically based diagnostic criteria. For example, in our explanation of the diagnostic criteria for dementia of the Alzheimer type, we wrote3:
"[O]f all of the criteria sets in DSM-IV, this is the one most likely tobecome quickly outdated. As of 1995, the definite diagnosis of Alzheimer disease can be made only by autopsy or brain biopsy. . . . Fortunately, research in this area is uncovering fascinating leads concerning the genetics and pathogenesis of this form of dementia. It seems likely that before DSM-V is published, diagnostic tests for Alzheimer disease will evolve that will supersede the current clinically based criteria set. This event should be a marvelous moment in the history of psychiatry, hopefully to be followed by . . . similar advances in the understanding and diagnosis of other psychiatric conditions (eg, schizophrenia, bipolar disorder)."
Unfortunately, our hopes for the development of diagnostically specific tests that could be included in the DSM-V criteria sets for Alzheimer disease have not been borne out. One of the 12 research planning conferences, convened with the goal of reviewing the scientific literature in advance of starting formal work on DSM-V, focused on diagnostic issues in dementia.4 Biomarkers (eg, cerebrospinal fluid t) have been identified that have sufficient diagnostic sensitivity and specificity to distinguish between patients with Alzheimer disease and normal healthy controls; however, these markers have not been demonstrated to be useful in differentiating Alzheimer dementia from other types of dementia. This, of course, is precisely the diagnostic scenario most likely to be faced by the psychiatrist in actual clinical settings.5
The lack of diagnostic sensitivity and specificity is even more the case for putative biomarkers in other diagnostic categories.6 The essential problem is that despite recent scientific advances, the study of the causes of mental disorders remains remarkably complex: for example, while it initially appeared possible to discover the “gene” behind a particular mental disorder, it is now clear that disorders are caused by a complex interaction of genes and the environment.7
It therefore seems likely that although the text of DSM-V will be enriched by the fruits of neurobiological research from the past 20 years, neurobiology and genetics will not inform the development of diagnostic criteria in DSM-V.8 Diagnostic criteria will therefore continue to be based on clinical findings. Cumulative research into the underlying pathophysiology of disorders may have an impact on the organization of the diagnostic groupings in DSM-V, however.9
Disorder groupings in DSM-IV, like diagnostic criteria, are based entirely on superficial symptoms. For example, the only thing that the disorders in the somatoform section of DSM-IV have in common is that affected patients are most likely to present in general medical settings. Several of the DSM-V research conferences focused on exploring possible opportunities to reorganize DSM-V that would reflect commonalities between disorders based on underlying pathophysiological and genetic factors rather than presenting symptoms.
For example, obsessive-compulsive disorder (OCD) is currently classified among the anxiety disorders in DSM-IV. This classification is based on the observation that patients with OCD typically present with anxiety resulting from their obsessions and compulsions. Besides this superficial similarity, however, OCD appears to have little in common with the other anxiety disorders in terms of treatment response (eg, OCD responds only to medications that affect the serotonin system whereas other anxiety disorders respond to a broader range of medications), family history, neurocircuitry, and comorbidity patterns. These dissimilarities suggest that OCD belongs in a separate diagnostic grouping.
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