Do psychotic, minor and intermittent depressive disorders exist on a continuum?

The following paper uses information from a family study and 10-year follow-up of probands with unipolar depression to describe relationships between psychotic and non-psychotic major depressive disorder (MDD) and, in turn, between psychotic MDD and minor or intermittent depressive disorders. Probands began follow-up as they sought treatment for MDD at any of five participating academic centers. Follow-up evaluations then occurred at 6-month intervals for 5 years and then annually for an additional 5 years. Two-thirds of the probands also entered a family study in which raters attempted direct interviews of all available adult first-degree relatives. Findings that individual symptoms comprising the endogenous MDD subtype had higher severity ratings, that the full MDD syndrome was present for a greater number of weeks in each year of follow-up, and that time to new episodes of MDD were shorter, all indicated that patients with psychotic features had a severe variant of MDD. An increased familial risk for psychotic MDD per se, and a sustained tendency for psychotic features to recur, indicated an important discontinuity, however. The increase in morbidity over time which characterized psychotic patients manifested in the full MDD syndrome, but not in mild MDD, minor or intermittent depressive syndromes. These milder syndromes tended to be more prominent over time among patients who began with non-psychotic MDD. This fails to support a continuum spanning both psychotic MDD and the mild, subsyndromal forms of unipolar depression.