Misdiagnosed bipolar depression has subtle clinical features

By Sara Freeman, medwireNews Reporter

Increased appetite, sleep, and weight gain, among other clinical features, can be used to help identify patients with bipolar disorder (BD) who have been misdiagnosed with major depressive disorder (MDD).

A Chinese study that looked at the sociodemographic and clinical features of BD in 1487 patients originally diagnosed with MDD shows that around 20% of patients were misclassified.

Yu-Tao Xiang (Chinese University of Hong Kong, China) and team found that 7.9% of patients with MDD actually had bipolar I disorder (BD-I) and 12.8% had bipolar II disorder (BD-II).

As failure to adequately treat BD can result in poorer outcomes, "correctly diagnosing BD in depressed patients has vitally important clinical implications," they write in Bipolar Disorders.

This trial was part of an ongoing, nationwide study initiated by the Chinese Society of Psychiatry. Participants were recruited from 13 major psychiatric hospitals or units. Patient DSM-IV diagnoses of MDD, BD-I, or BD-II were made using the Mini International Neuropsychiatric Interview.

Compared with MDD patients, BD-I patients were twice as likely to have atypical depressive features, such as an increased appetite, increased sleep, and weight gain, and twice as likely to have psychotic symptoms. They also tended to have more lifetime depressive episodes and an earlier age of onset.

Similarly, BD-II patients were twice as likely to have psychotic symptoms as MDD patients and had an earlier age of onset.

BD-I patients could be distinguished from BD-II patients due to being significantly more likely to have more frequent depressive episodes per year (odds ratio=3.1).

Xiang et al note that it may take 8 to 10 years for BD to be accurately diagnosed. They suggest that it is frequently classified as MDD because patients may not consider hypomania to be a problem and subsequently underreport it. They may also have not yet experienced hypomania, and clinicians may fail to ask about hypomania in patients with depression. These factors can all lead to delay in prescribing appropriate treatment.

"Our results indicate that there are subtle differences between the forms of depressive episodes occurring in the context of BD and MDD," the researchers observe. They suggest that these differences could be used to help improve and guide diagnostic practices in China.

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