It also found that bipolar disorder does not appear to be associated with treatment resistance in patients with depression, a finding that challenges the common theory that some cases of difficult-to-treat depression are actually unrecognised bipolar disorder, the researchers added.
They conducted the study to assess the link between bipolar disorder and treatment outcomes among 4,041 patients with depression. The patients first received the antidepressant citalopram (Celexa), followed by up to three next-step treatments, depending on their responses.
At the start of the study, 1,198 (30%) of the patients said they had experienced at least one psychotic symptom - such as believing they had special powers or were being controlled or plotted against - in the previous six months. These patients were significantly less likely to respond to treatment.
In addition, 1,524 patients (38.1%) said they had experienced at least one symptom of bipolar disorder in the previous six months. Of those symptoms, irritability was associated with poor treatment outcomes.
But several indicators commonly associated with bipolar disorder - including history of manic symptoms and family history of the condition - were not associated with patient responses to antidepressants, the researchers said.
The study was published in the Archives of General Psychiatry.
What the findings mean
"Considered as a whole, our results cast doubt on the frequent assertion that unrecognised bipolar disorder is widespread in clinical practise and particularly in treatment-resistant major depressive disorder," the researchers concluded, led by Dr Roy H. Perlis, of Massachusetts General Hospital and Harvard Medical School.
"Screening for bipolar disorder among psychiatric patients remains important, as does considering individual risk factors such as family history or age at onset. Still, our findings indicate that, in most individuals presenting with a major depressive episode without a prior manic or hypomanic episode, unrecognised bipolarity does not appear to be a major determinant of treatment resistance," the researchers said.
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