Background: Treatment-resistant depression is a heterogeneous entity. There are many variables associated with poor response to antidepressants, one of which is missed bipolarity. Therefore, the present study investigated the bipolar diathesis between patients with treatment-resistant (TR) depression and non-treatment-resistant (NTR) depression as assessed with the Mood Disorder Questionnaire (MDQ).
Method: The population studied included 1051 patients diagnosed with single or recurrent major depressive disorder. They were classified into a non-treatment-resistant group (481 patients) and a treatment-resistant group (570 patients). The psychiatrist, using information from the patient's medical history, psychiatric examination and available documentation, assessed each eligible patient. The symptoms of bipolarity were additionally assessed by the Mood Disorder Questionnaire.
Results: A positive screen on the MDQ defined as endorsement of at least 6 of the 13 yes or no questions was an independent risk factor for treatment resistance.The total MDQ score was significantly higher in TR vs NTR (4.33 vs 2.66 points p<0.001) and the percentage of patients screened positive was significantly higher in TR than in NTR (13.7% vs 5.6% p<0.001). Factor analysis resulted in 2 factors with eigenvalues >1 explaining 91.5% of total variance.
Conclusions: Using the MDQ scale we confirmed the association between bipolarity and worse response to antidepressant drugs in patients with major depressive disorder.
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