The symptoms of depression in bipolar disorder are the same as in major depression.  In fact the depressive episode of bipolar disorder meets the same criteria outlined for a major depressive episode in the DSM-IV-TR, as described in Question 12.  The differences between the illnesses have more to do with their genetics, clinical course, prognosis, and treatment.  Bipolar disorder is so often missed because the depressive episodes look the same; it takes an average of eight years for the correct diagnosis of bipolar disorder to be made in a person who presents for treatment of depression.  Frequently patients fail to report a history of hypomanic or manic symptoms, but clinicians may fail to recognize past manic symptoms as well.  Bipolar II disorder is more likely to be missed than bipolar I due to the reduced severity of hypomanic symptoms.  It is the history that is important in making an accurate diagnosis of bipolar disorder in a depressed individual.  Some clinical features, however, are thought more indicative of bipolar disorder than major depression.  These include a younger age of onset (< 25 years old), presence of atypical symptoms, psychotic symptoms, and comorbid substance abuse.  A family history of bipolar illness is also suggestive.  Other associations include multiple depressive episodes, brief duration of depressive illness, and antidepressant-induced mania or hypomania.  Although none of these associations are diagnostic of bipolar depression, they can alert a clinician to watch for uture manic episodes.

Although primary care physicians often diagnose cases of depression, including a bipolar depressive episode, because of the unique difficulties in treating bipolar depression, it is critical that a psychiatrist closely follow the treatment course.  Treatment of bipolar depression can be difficult because the use of antidepressant therapy poses risks for a manic switch.  Lithium has historically been the mainstay for bipolar depression and has been shown to reduce risk of suicide in bipolar patients, but it has numerous side effects.  Recent approval was obtained for the combination of olanzapine and fluoxetine (Symbyax) specifically for bipolar depression.  Anticonvulsant medications have been preferentially utilized for treatment of manic episodes.  Lamotrigine has been approved for prevention of depressive recurrences in bipolar disorder.  If a psychiatrist determines that an antidepressant is neccessary, current practice is to have a mood stabilizer on board prior to initiating the antidepressant, as this may be protective of a manic switch from the antidepressant.