Weekly affective symptom severity and polarity were compared in 135 bipolar I (BP I) and 71 bipolar II (BP II) patients during up to 20 yr of prospective symptomatic follow-up. The course of BP I and BP II was chronic; patients were symptomatic approximately half of all follow-up weeks (BP I 46.6% and BP II 55.8% of weeks). Most bipolar disorder research has concentrated on episodes of MDD and mania and yet minor and subsyndromal symptoms are three times more common during the long-term course. Weeks with depressive symptoms predominated over manic/hypomanic symptoms in both disorders (3[ratio ]1) in BP I and BP II at 37[ratio ]1 in a largely depressive course (depressive symptoms=59.1% of weeks vs. hypomanic=1.9% of weeks). BP I patients had more weeks of cycling/mixed polarity, hypomanic and subsyndromal hypomanic symptoms. Weekly symptom severity and polarity fluctuated frequently within the same bipolar patient, in which the longitudinal symptomatic expression of BP I and BP II is dimensional in nature involving all levels of affective symptom severity of mania and depression. Although BP I is more severe, BP II with its intensely chronic depressive features is not simply the ‘lesser’ of the bipolar disorders; it is also a serious illness, more so than previously thought (for instance, as described in DSM-IV and ICP-10). It is likely that this conventional view is the reason why BP II patients were prescribed pharmacological treatments significantly less often when acutely symptomatic and during intervals between episodes. Taken together with previous research by us on the long-term structure of unipolar depression, we submit that the thrust of our work during the past decade supports ‘classic’ notions of a broader affective disorder spectrum, bringing bipolarity and recurrent unipolarity closer together. However the genetic variation underlying such a putative spectrum remains to be clarified.
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