Association between the so-called "activation syndrome" and bipolar II disorder, a related disorder, and bipolar suggestive features in outpatients with depression

Activation syndrome (AS) is a cluster of symptoms listed by the US Food and Drug Administration as possible suicidality precursors during antidepressant treatment. We aimed to clarify whether AS is associated with bipolar II disorder (BP-II) and its related disorder, i.e., bipolar disorder not otherwise specified (BP-NOS), which are often mistreated as major depressive disorder (MDD), as well as bipolar suggestive features in outpatients with depression.

The frequency of AS, bipolar suggestive features, and background variables in consecutive outpatients with a major depressive episode (MDE) due to BP-II/BP-NOS or MDD, who were naturalistically treated with antidepressants, were investigated and analyzed retrospectively.

Of 157 evaluable patients (46 BP-II/BP-NOS, 111 MDD), 39 (24.8%) experienced AS. Patients with BP-II/BP-NOS experienced AS significantly more frequently than patients with MDD (52.2% of BP-II/BP-NOS vs. 13.5% of MDD, p<0.01). Univariate analysis revealed that BP-II/BP-NOS diagnosis, cyclothymic temperament, early age at onset of first MDE, psychiatric comorbidities, and depressive mixed state (DMX) were significantly associated with AS development in the entire sample. Multivariate analysis revealed that BP-II/BP-NOS diagnosis and DMX were independent risk factors for AS.

This is a retrospective and naturalistic study; therefore, patient selection bias could have occurred.

Cautious monitoring of AS is needed during antidepressant trials in patients with BP-II/BP-NOS. Clinicians should re-evaluate underlying bipolarity when they confront AS. Antidepressants should be avoided for treating a current DMX beyond the unipolar-bipolar dichotomy. Prospective studies are needed to confirm these results.