The groups tasked with revising the DSM and ICD systems shared the overarching goal of harmonizing the two classifications as much as possible, for the following reasons: . The existence of two major classifications of mental disorders hinders the collection and use of national health statistics, the design of clinical trials aimed at developing new treatments, and the consideration of global applicability of the results by international regulatory agencies.
0 More broadly, the existence of two classifications complicates attempts to replicate sci- entific results across national boundaries.
0 Even when the intention was to identify identical patient populations, DSM-IV and
ICD-10 diagnoses did not always agree.
Early in the course of the revisions, it became apparent that a shared organizational structure would help harmonize the classifications. In fact, the use of a shared framework helped to integrate the work of DSM and ICD work groups and to focus on scientific is- sues. The DSM-S organization and the proposed linear structure of the ICD-11 have been endorsed by the leadership of the NIMH Research Domain Criteria (RDoC) project as con- sistent with the initial overall structure of that project.
Of course, principled disagreements on the classification of psychopathology and on specific criteria for certain disorders were expected given the current state of scientific knowledge. However, most of the salient differences between the DSM and the ICD classi- fications do not reﬂect real scientific differences, but rather represent historical by-products of independent committee processes.
To the surprise of participants in both revision processes, large sections of the content fell relatively easily into place, reﬂecting real strengths in some areas of the scientific lit- erature, such as epidemiology, analyses of comorbidity, twin studies, and certain other ge- netically informed designs. When disparities emerged, they almost always reﬂected the need to make a judgment about where to place a disorder in the face of incomplete—or, more often, conﬂicting—data. Thus, for example, on the basis of patterns of symptoms, co- morbidity, and shared risk factors, attention-deficit/hyperactivity disorder (ADHD) was placed with neurodevelopmental disorders, but the same data also supported strong ar- guments to place ADHD within disruptive, impulse-control, and conduct disorders.
These issues were settled with the preponderance of evidence (most notably validators ap- proved by the DSM-5 Task Force). The work groups recognize, however, that future dis- coveries might change the placement as well as the contours of individual disorders and, furthermore, that the simple and linear organization that best supports clinical practice may not fully capture the complexity and heterogeneity of mental disorders. The revised organization is coordinated with the mental and behavioral disorders chapter (Chapter V) of ICD-11, which will utilize an expanded numeric—alphanumeric coding system. How- ever, the official coding system in use in the United States at the time of publication of this manual is that of the International Classification of Diseases, Ninth Revision, Clinical Modifica- tion (ICD-9-CM)—the U.S. adaptation of ICD-9. International Classification of Diseases, Tenth
Revision, Clinical Modification (ICD-lO-CM), adapted from ICD-10, is scheduled for imple- mentation in the United States in October 2014. Given the impending release of ICD-ll, it was decided that this iteration, and not ICD—lO, would be the most relevant on which to focus harmonization. However, given that adoption of the ICD-9-CM coding system will remain at the time of the DSM-5 release, it will be necessary to use the ICD-9-CM codes. Further- more, given that DSM-S’s organizational structure reﬂects the anticipated structure of
ICD-11, the eventual ICD-11 codes will follow the sequential order of diagnoses in the
DSM-5 chapter structure more closely. At present, both the ICD—9-CM and the ICD-10-CM codes have been indicated for each disorder. These codes will not be in sequential order throughout the manual because they were assigned to complement earlier organizational structures.
Dimensional Approach to Diagnosis