Prevalence and Clinical Correlates of Residual Depressive Symptoms in Bipolar II Disorder

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Abstract
Background: Most patients with unipolar and bipolar I disorder have residual symptoms, despite successful treatment. The appraisal of subsyndromal symptomatology has important implications for pathophysiological models of disease and relapse prevention. Residual symptoms in bipolar II disorder were studied insufficiently. The study of residual symptoms in bipolar II disorder is important, because many depressed outpatients may suffer from it and because bipolar II disorder may be distinct from type I. The study aims were to assess the prevalence and clinical correlates of persistent residual depressive symptoms in bipolar II disorder. Methods: 138 consecutive patients with bipolar II disorder and 83 unipolar disorder outpatients, presenting for major depressive episode treatment in private practice, were interviewed with the Structured Clinical Interview for DSM-IV Axis I Disorders – Clinician’s Version. Study variables were persistent (more than 2 years) residual depressive symptoms, age, gender, age at onset, illness duration, recurrences, axis I comorbidity, severity, psychotic, melancholic and atypical features. Results: The prevalence of residual depressive symptoms was 44.9% in bipolar II disorder and 43.3% in unipolar disorder. Residual depressive symptoms in bipolar II and unipolar disorders were significantly and positively associated with illness duration and recurrences. Conclusions: Persistent residual depressive symptoms were common in bipolar II disorder. Residual unipolar and bipolar II depressive symptoms were related to duration of illness and number of recurrences. Reducing these variables could reduce and prevent residual symptoms. A mechanism of kindling (more mood episodes leading to worse outcome) could be that of leaving a larger and larger amount of residual symptoms after the acute episode has subsided.