[The modern concept of atypical depression: four definitions].

This report describes and compares four current concepts and definitions of atypical depression. Since its emergence, atypical depression has been considered a depressive state that can be relieved by MAO inhibitors. Davidson classified the symptomatic features of atypical depression into type A, which is predominated by anxiety symptoms, and type V, which is represented by atypical vegetative symptoms, such as hyperphagia, weight gain, oversleeping, and increased sexual drive. Features that are shared by both subtypes include: early onset, female predominance, outpatient predominance, mildness, few suicide attempts, nonbipolarity, nonendogeneity, and few psychomotor changes. Based on these features, bipolar depression can also be defined as atypical depression type V. Herein, we examine and classify four concepts of atypical depression according to the endogenous-nonendogenous (melancholic-nonmelancholic) and unipolar-bipolar dichotomies. The Columbia University group (see Quitkin, Stewart, McGrath, Klein et al.) and the New South Wales University group (see Parker) consider atypical depression to be chronic, mild, nonendogenous (nonmelancholic), unipolar depression. The former group postulates that mood reactivity is necessary, while the latter asserts the structural priority of anxiety symptoms over mood symptoms and the significance of interpersonal rejection sensitivity. For the Columbia group, the significance of mood reactivity reflects the theory that mood nonreactivity is the essential symptom of "endogenomorphic depression", which was proposed by Klein as typical depression. Thus, mood reactivity is not related to overreactivity or hyperactivity, which are often observed in atypical depressives. However, Parker postulates that psychomotor symptoms are the essential features of melancholia, which he recognizes as typical depression; therefore, the New South Wales group does not recognize the significance of mood reactivity. The New South Wales group accepts the relationship between anxiety symptoms and interpersonal rejection sensitivity, while the Columbia group does not recognize the importance of anxiety symptoms because they could not identify a relationship between such symptoms and the efficacy of MAO inhibitors. The concept of atypical depression proposed by the New South Wales group overlaps considerably with that of hysteroid dysphoria, which was proposed by Klein et al., and was the progenitor of Columbia group's concept of atypical depression. The Pittsburgh University group (see Himmelhoch, Kupfer, Thase et al.) and the soft bipolar spectrum group (see Akiskal, Perugi, Benazzi et al.) regard atypical depression as a depressive state that can be observed in bipolar disorder. The former groups takes into account reversed vegetative symptoms and lethargy as signs of bipolar disorder, while the latter recognizes that atypical depression shares features with bipolar II disorder or soft bipolar spectrum disorder. The soft bipolar spectrum group maintains their unique concept of bipolar disorder, which regards some unipolar depressions as bipolar disorder, while the Pittsburg group continues to share the conventional concept of a unipolar-bipolar dichotomy with other groups. The fundamental pattern of atypical depression is represented by chronic mild depressions, which are characterized by a younger age at onset, female predominance, interpersonal rejection sensitivity, and mood lability, which are difficult to distinguish from a characterological pathology. Patients who present with such patterns are frequently diagnosed with borderline, histrionic, or avoidant personality disorders; therefore, we must recognize the significance of atypical depression as a concept that can suggest the utility of medication for these patients. For such patients, however, various groups have proposed different kinds of definition and therapeutic guidelines that are difficult to synthesize and utilize in clinical settings. Moreover, some features of atypical depression outlined in the Columbia University criteria, such as a younger age at onset, chronicity, mildness, and female predominance, were excluded from DSM-IV. Consequently, the concept of atypical depression has become overextended and gradually lost its construct validity. Therefore, the diagnostic criteria for atypical depression should be reconsidered in reference to various definitions and concepts and refined through accumulated clinical research.