Antidepressant emergent mood switch in major depressive disorder: onset, clinical correlates and impact on suicidality.

Antidepressant (AD)- emergent mood switch (AEMS) is a common complication of bipolar depression. This study aimed to investigate the prevalence and clinical correlates of subthreshold AEMS (i.e. not fulfilling DSM criteria for hypomanic episodes) in major depressive disorder (MDD) and, prognostically, its impact on AD treatment outcome and suicidality. The study involved 425 outpatients with MDD followed during the acute phase (12 weeks) and continuation (weeks 13-28) AD treatment. AEMS was assessed through the Altman Self-Rating Mania scale (ASRM ≥ 6). Several clinical features differentiated individuals with or without subthreshold AEMS (n = 204 vs. 221): negative self-perception [odds ratio (OR) 1.017-1.565]; panic disorder (OR 1.000-1.091); subthreshold hypomanic episodes (OR 1.466-13.352); childhood emotional abuse (OR 1.053-2.447); lifetime suicidal behaviour (OR 1.027-1.236); AD-related remission (χ 2  = 22.903 P  < 0.0001) and suicide ideation (χ 2  = 16.701 P  < 0.0001). In AEMS earlier onset showed a strong correlation with bipolar spectrum disorder (overall score: P  = 0.0053; mixed depression: P  = 0.0154; subthreshold hypomania: P  = 0.0150) whereas late-onset was associated with more severe suicidal behaviour ( P  < 0.001). In conclusion, our results demonstrate that subthreshold mood switches occur frequently in unipolar depression during acute AD treatment as well as in continuation phase. Time of switch onset seems to have the greatest diagnostic and prognostic value.