|1.4.1 Unipolar Depressive Disorder and Bipolar Depression|
Unipolar depressive disorder, from a diagnostic point of view, requires the presence of a single major depressive episode. According to DMS-IV and its diagnostic instruments, the key symptoms and duration are similar to the bipolar depressive episode. The primary unipolar disorders are also distinguished between a single episode or recurrent. The recurrent subtype has also been associated with bipolar disorder, especially when the depressive episodes are briefer than the usual two week period (Angst and Dobler-Mikola, 1985) specified in DSM-IV.
From a phenomenological point of view however research has shown interesting and consistent differences between unipolar and bipolar disorder. Leonhard (1957) early on discussed that his bipolar patients presented with more symptomatic variability from episode to episode than his unipolar patients who presented with more stereotyped symptom profiles.
A review of several decades of studies by (Goodwin and Jamison, 2007, pp. 16-17), identified that overall Bipolar depression is characterised by higher levels of psychomotor retardation, tension/fearfulness, atypical features, depressive mixed states, symptomatic variability across episodes, lability within episodes, irritability, late insomnia and hypersomnia, fragmented REM sleep, and psychotic features. On the other hand unipolar depression tends to have higher levels of anxiety, somatic complaints, psychomotor agitation, early insomnia, appetite and weight loss. It is worth noting that the majority of the studies reporting these differences have been referring to syndromal unipolar and bipolar states. Of course there is nothing to suggest that the sub-syndromal picture is likely to be different but such data are yet lacking.
The individual symptoms that may be present during the “well” sub-syndromal phases of the disorder merit further study. Such symptoms may have different contributions to the functional burden documented by bipolar sub-syndromal states and also may have different weights in predicting relapse or time spent in syndromal states.
Angst, J. & Dobler-Mikola, A. 1985. The Zurich Study--a prospective epidemiological study of depressive, neurotic and psychosomatic syndromes. IV. Recurrent and nonrecurrent brief depression. Eur Arch Psychiatry Neurol Sci, 234, 408-16.