Panel 2

Challenges and clinical strategies in the diagnosis of bipolar disorder

Reasons for the difficulty in bipolar disorder diagnosis

• Diagnostic criteria for depressive episodes: are identical in bipolar disorder and unipolar depression. Bipolar disorder is thus often misdiagnosed as unipolar depression.
• Many different bipolar disorder subtypes exist. Bipolar disorder type II is especially difficult to distinguish from unipolar depression, because of frequent depressive episodes and the absence of full-blown mania.
• Depressive symptoms are common in bipolar disorder and their prevalence is higher than that of hypomanic or manic symptoms.
• Mixed mood episodes are more common than was previously thought in bipolar disorder. These episodes might obscure detection of mania and hypomania, in view of the reporting bias towards depressive symptoms in people with bipolar disorder seeking treatment.
• Subthreshold symptoms of hypomania are common in unipolar depression. These symptoms might be more common than was previously thought; they are present in 30–55% of people during a depressive episode and are common in unipolar depression. At least a subset of patients with treatment-resistant unipolar depression might have misdiagnosed bipolar disorder.