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DSM-V, Dimensional Approach, by Roger Peele, MD
DSM-V: Is a Dimensional Approach the Answer?
Roger Peele, MD, DLFAPA, Enrico Suardi, MD, and Nancy K. Wahls, MD
Maryland is well-represented in the development of DSM-V. Nine of the 28-member APA DSM-V Task Force live or work in Maryland: William Carpenter, Wilson Compton, Howard Moss, William Narrows, Roger Peele [one of the authors], Daniel Pines, Darrel Regier, Susan Swedo, and Philip Wang.
While the Task Force has just begun its work, five major foci are already clear.
1. Lifespan developments as they influence diagnosis.
2. The interface between psychiatry and the rest of medicine, a boundary that we want to de-emphasize.
3. Greater sensitivity to cultural and gender factors relevant to diagnosis, so that psychiatric diagnosis does not fail people from other cultures or from one or the other gender.
4. The relationships between disorders.
5. The possibility of supplementing, or replacing, the categorical approach with a dimensional approach.
The last item (#5) is of most interest to the typical clinician and the focus of this article.
DSM IV diagnoses are categorical in nature, which means that any particular diagnosis is either present or absent. Someone with four out of nine symptoms of major depression is said not to have major depression; with five out of nine symptoms—“voila!” the patient has major depression. In a sense, it is an “all or nothing” system of diagnosing.
A dimensional approach, on the other hand, includes variables and allows for degrees of diagnosis. This approach has more depth and, many argue, more clinical relevance. Similar systems are used for blood pressure, cardiac risk scales, renal failure rating scales, and other medical conditions.
The PHQ-9 (Patients’ Health Questionaire – 9) is an example of a dimensional approach to depression. Each of the nine DSM criteria is rated as “not at all,” “several days,” “more than half the days,” and “nearly every day.” This scale provides a quantifiable indicator of the diagnosis of depression and its severity, while also including valuable descriptive information. By facilitating and standardizing monitoring of treatment response, it might serve eventually as an indicator of prognosis.
In DSM-IV-TR, about half of the 374 entities are tied to an etiology: substance-related, neurological, general medical, trauma or stress-related, seasonal, and/or puerperal. The dimensional approach’s main focus is the non-etiological psychopathology, the other half. There is very little evidence that non-etiological psychopathology is divided up in nature as DSM-IV-TR proposes.
Much of the work on dimensions has focused on personality disorders. Below we highlight a proposal that has just five dimensions for personality. A clinician using this proposal would rate a patient on each of these five dimensions; only extremes at either end would be regarded as pathological.
1. Extraversion versus introversion
2. Antagonism versus compliance
3. Constraint versus impulsivity
4. Emotional dysregulation versus emotional stability
5. Unconventionality versus closedness to experience
Note that three of the typical characteristics of borderline personality disorders can be described in items 2, 3 and 4: most “borderlines” are excessively antagonistic, impulsive and emotionally unstable.
Unlike categorical diagnoses, these five dimensions can describe both the well and the sick. This dimensional approach defines traits not syndromes. Unlike categorical diagnoses, a dimensional approach to diagnosis also has potentially greater reliability and validity. These five scales can be far more exact, diagnostically, than DSM-IV’s relatively heterogeneous borderline personality disorder category, with its five (or more) of nine signs and symptoms, which includes at least 256 varieties. Most of us find that current diagnostic categories place patients in ill-fitting diagnostic procrustean beds. Despite potential problems, a dimensional approach will feel very real to many of us. Patients present with signs and symptoms. Would the dimensional approach free the clinician to capture the patient’s individuality without implying any additional psychopathology?
The dimensional approach seems to be more consistent with today’s concepts of psychopathology and with medicine’s interest in the impact of traits on medical illnesses. It is also potentially more reliable than the categorical approach. Finally, many find it desirable because of its rationality.
So why not adopt these dimensions?
First, the proposals are only rational, not empirical. We have yet to see controlled studies that show clinicians who use a dimensional approach obtain better clinical results than those who use the categorical approach.
Second, cut-off points are going to be difficult to establish. What is normal and what is pathological? Should levels of antagonism versus compliance be the same in all settings? Are there not some situations in which antagonism is lifesaving and other situations in which compliance is lifesaving?
Third, what about the present categorical definitions of personality disorders? Could they continue in DSM-V (hopefully, without the word “personality” in the title, a word that unnecessarily pains patients and postpones treatment)?
Fourth, what about the worthy experts who have given their careers to enhancing our understanding of DSM-IV’s categorical disorders? How much is lost if DSM-V makes pre-DSM-V data obsolete? If DSM-V throws out DSM-IV’s categories, should the American Psychiatric Association give these experts “golden parachutes”? But more than a researcher’s lifework is at stake. How much of the “scientific basis” of clinical work is unraveled if we move to a dimensional approach? Some of the data based on scales can be revisited easily, but not all of them. And, although the APA Assembly has called for the Food and Drug Administration’s approval of treatment for signs and symptoms rather than only for DSM-IV categories, 99+% of the approvals are still tied to categories.
DSM-V is not due to be published until 2012; however, the DSM-V Task Force is expected to have an initial draft of DSM-V in 2009. At that point, we will know better how far along the thinking has moved toward a dimensional approach.