MedWire News: Bipolar I disorder patients with a lifetime history of exclusively mixed, but not manic, episodes are at increased risk for suicide and have higher comorbidity rates than other patients with the condition, study results show.
However, "current DSM-IV-TR criteria do not correctly classify these patients, which may lead to inadequate treatment," say the researchers.
Writing the Journal of Affective Disorders, Eduard Vieta (University of Barcelona, Spain) and team explain that, according to DSM-IV-TR criteria, mixed episodes are limited to bipolar I disorder and require both manic and depressive episodes each day for at least 1 week, that either socio-professional and/or everyday life impairment or psychosis be present, and that medical conditions and drugs do not account for symptoms.
But they say that "limiting mixed states to bipolar I disorder disregards the clinical relevance of subthreshold mixed symptoms occurring in the context of a broader bipolar spectrum, with relevant clinical and treatment implications."
To investigate the possible existence of a "bipolar-mixed continuum," the team studied 134 inpatients diagnosed with bipolar I disorder who were admitted to hospital in 2009 for a major affective acute episode (depressive, manic or mixed index episode).
The participants were divided into three groups based on lifetime history of purely manic episodes without mixed features (PMA, n=46), lifetime history of both manic and mixed episodes (MIX, n=53), and lifetime history of exclusively mixed, but not manic, episodes (PMIX, n=35).
All of the patients were assessed for demographic data, number and polarity of episodes, number and duration of hospitalizations, age at onset, polarity of first episode, predominant polarity, lifetime history of psychosis, suicidal behavior, Axis I and Axis II comorbidities, substance abuse, and other variables.
The researchers found that PMIX patients had significantly higher rates of depressive-predominant polarity than PMA and MIX patients, at 42.9% versus 13.0% and 11.3%, respectively, and were less likely to have a lifetime history of psychotic symptoms, at 31.4% versus 63.0% and 75.5%, respectively.
PMIX patients were also more likely to have a history of suicide attempts than PMA and MIX patients, at 60.0% versus 17.4% and 28.3%, respectively, and had higher rates of Axis I comorbidity, at 54.3% versus 28.3% and 43.4%, respectively.
Furthermore, PMIX patients had received more antidepressants during their lifetime and in the 6-month period prior to the index episode than those in the other patient groups.
Vieta and team conclude: "PMIX is likely to have a higher risk for suicide and higher rates of comorbidities; current DSM-IV-TR criteria are not fit for correctly classifying these patients and this may affect treatment appropriateness.
They add: "The concept of 'mixicity' should be extended beyond bipolar I disorder to other bipolar disorder subtypes."
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