Patients with depression manifest several symptoms that do not appear to be connected to resistance to treatment.
This is evidence against the common hypothesis that some cases of difficult-to-treat depression are actually unrecognised bipolar disorder, according to a new study.
"The distinction between major depressive disorder and bipolar disorder remains a challenging clinical problem when individuals present with a major depressive episode," the authors wrote.
"The identification of individuals at risk for bipolar disorder is of more than academic importance, as treatment may be markedly different; in particular, antidepressants have been suggested to exacerbate the illness course of at least a subset of bipolar individuals," they added.
Roy H. Perlis of Massachusetts General Hospital and Harvard Medical School, Boston, and colleagues studied 4,041 adults with a diagnosis of depression. Patients were treated with the antidepressant citalopram, followed by up to three next-step treatments as needed depending on their response.
Almost one-third (1,198, or 30 percent) of the patients reported having at least one psychotic symptom in the previous six months. Those who did were significantly less likely to go into remission over all the treatment periods.
1,524 patients (38.1 percent) with depression described at least one manic-like symptom.
"On the other hand, several indicators consistently associated with bipolar disposition in the literature, including history of manic symptoms and family history of bipolar disorder, were not associated with outcome of treatment with antidepressants in the STAR*D study," the authors wrote.
"Briefer episode duration, suggested to represent a risk marker for bipolarity, was associated with greater likelihood of remission."
"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, unrecognized bipolarity does not appear to be a major determinant of treatment resistance."
The study will appear in the April 2011 print issue of Archives of General Psychiatry.