In recent years increased indices of bipolarity in treatment-resistant depression were found. The objective of the study was to assess and compare Mood Disorder Questionnaire (MDQ) positive screen between patients with treatment-resistant (TR) depression and non-treatment-resistant (NTR) depression and identify significant predictors of MDQ positive screen.

The population studied included patients aged 18-65 who had a diagnosis of first or recurrent major depressive disorder. Each psychiatrist included 5 consecutive patients, from all the patients he is treating, where the depressive episode was assessed as treatment-resistant (study group) and 5 consecutive patients with a non-treatment-resistant episode (control group). The symptoms of bipolarity were assessed by the MDQ. A positive screen of MDQ showing the features of bipolarity requires seven or more items be endorsed, at least several of the items co-occurred, and the symptoms caused at least moderate psychological impairment. One thousand and fifty-one patients entered the study: 570 in treatment-resistant group and 481 in non-treatment-resistant group.

The percentage of patients having MDQ positive screen was significantly higher in the treatment-resistant than in the non-treatment-resistant group (13.7% vs. 5.6%, respectively, p< 0.001). Significant predictors of MDQ positive screen identified in logistic regression were: family history of bipolar disorder (OR=4.04, p< 0.001), early onset of first major depression (< 20 years) (OR=3.27, p=0.001), and incomplete last remission (OR=3.11, p< 0.001).

Our results may suggests bipolar diathesis in treatment- resistant depression.