By Laura Cowen, medwireNews Reporter
Using the most recent diagnostic criteria increases the prevalence of mixed features in patients with bipolar disorder more than threefold, study findings indicate.
Of 331 patients diagnosed with bipolar disorder according to the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, Text Revision (DSM-IV-TR) criteria between 2003 and 2013, 6.0% were classed as having mixed episodes.
However, this rate increased significantly to 19.6% when Won-Myong Bahk (The Catholic University of Korea, Seoul, South Korea) and colleagues recategorised the patients according to the DSM, Fifth Edition (DSM-5) criteria.
The researchers explain that, according to the DSM-IV-TR criteria “the diagnosis of a mixed episode applies only to patients with bipolar I disorder who exhibit the simultaneous presence of full manic and full depressive symptoms for at least 1 week.”
This narrow definition was expanded in DSM-5 to take “a more dimensional perspective” that includes the ‘with mixed features’ specifier. This specifier can be applied to episodes of mania/hypomania in which depressive features are present and to episodes of depression in the context of major depressive disorder or bipolar disorder when features of mania/hypomania are present, says the team.
In the present study, 59.5% of the mood episodes were manic/hypomanic, 34.4% were depressed, and 6.0% were mixed episodes when the patients were diagnosed according to the DSM-IV-TR criteria.
However, when using the DSM-5 definition and the ‘with mixed features’ specifier, 49.8% of mood episodes were manic/hypomanic, 30.5% were depressed, 15.7% were manic/hypomanic episodes with mixed features, and 3.9% were depressed episodes with mixed features.
“The additional patients identified using the DSM-5 criteria may represent patients with sub-syndromal and non-overlapping mixed features and could indicate that patients with mixed features are underdiagnosed”, Bahk et al remark.
Compared with patients without mixed features, those with mixed features had a significantly younger age of onset (21.6 vs 34.2 years), younger age at hospitalisation (25.2 vs 43.8 years), more frequent hospitalisations for mixed episodes (0.2 vs 0) and a tendency for a greater suicide risk (20.0 vs 7.1%) compared with patients without mixed features.
Writing in the Journal of Affective Disorders, Bahk and co-authors conclude that the differences they observed when patients were reclassified according to DSM-5 criteria “will help to identify bipolar disorder patients with mixed features in clinical practice and further the understanding of the clinical course, clinical characteristics, and pharmacological treatment of this bipolar disorder subtype.”
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