The depressive spectrum: diagnostic classification and course

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Abstract

The spectrum of depression is much wider than that reflected in the current diagnostic nomenclature. A large proportion of subjects with depression both in treatment and in the community fail to meet diagnostic criteria for either major depressive disorder (MDD) or dysthymia. Inclusion of subthreshold categories of depression dramatically improves the coverage of treated depression, particularly in community samples, and better enables the characterization of its longitudinal course.

This paper investigates the application of diagnostic criteria for both threshold and subthreshold categories of depression in a prospective longitudinal community study of young adults from Zurich, Switzerland. We present the prevalence and treatment rates of each of the depressive subtypes, the degree of diagnostic overlap and the longitudinal stability of subthreshold and threshold categories of depression.

The findings indicate that the prevalence rates of subthreshold categories of depression are quite high in the community, and that a substantial proportion of subthreshold depressives, particularly those with recurrent depression, receive treatment. There is a strong tendency for individuals to meet multiple depressive subtypes over time, with little stability of individual categories among those who continue to manifest depression over a 15-year period. The prospective longitudinal data reveal that major depression is both an antecedent to and sequela of subthreshold categories, providing evidence for the validity of the spectrum concept of depression. However, the need for a threshold for the symptom criteria is suggested by the lack of predictive value of minor depression and depressive symptoms only.

These results suggest that both the current symptom threshold for a depressive syndrome and recurrence, but not the minimum duration of depressive episodes, are important components of the classification of depression.

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Discussion of “The Depressive Spectrum: Diagnostic Classification and Course” Discussion led by George Winokur, M.D. from the University of Iowa

It is very clear that an increasing number of diagnostic categories are emerging in the field of mood disorders which underscores the poor longitudinal stability of these diagnostic categories or subtypes. In defining subtypes or categories, it is important to specify severity, relationship to other subtypes and threshold for diagnosis. In regard to recurrent brief depression, it is possible that duration of a syndrome may be less important than its recurrence which may be linked to a genetic vulnerability. We have been impressed with the emerging concensus about the fluidity of depressive symptoms within a variety of diagnostic categories and the associated impairment with current subthreshold depressive disorders.
General discussion

A group discussion then ensued about the number of depressive symptoms used to define different diagnostic categories within the mood disorders group. It was argued that investigation of the distribution of depressive mood disorder categories. However, extending the discussion, Dr. Winokur indicated that the number of symptoms may only be one aspect in definition of mood disorders and argued for the inclusion of other information such a family history which may aid in clarifying the heterogeneity of mood disorders.

Dr. Winokur also raised the issue that the range of symptoms, not currently associated with mood disorders, be considered in order to increase the information characterizing these disorders. For example, could there be a split similar to the one suggested for schizophrenia into positive or negative symptoms, that could be applied to mood disorders. Lastly, in addition to the natural history of the disorder, should the treatment history of the disorder be included in diagnostic considerations?

Dr. Angst ended the discussion period by describing some of his findings regarding the course of MDD from the Zurich sample. The different course patterns he has identified are as follows: single episode 15%, 4% chronic, 19% recurrent, 13% decaying recurrent, 4% recurrent with residual, 3% increasing residual and recurrent, and 42% with other patterns. Dr. Angst also indicated that these course descriptors should be considered in light of the different demographic and epidemiological characteristics of the sample at baseline.