The team found that children with subthreshold bipolar I disorder symptoms and impaired emotional regulation were at the highest risk for converting to bipolar I disorder during an average follow-up of 11.4 years.
Joseph Biederman (Massachusetts General Hospital, Boston, USA) and colleagues say that previous studies have pinpointed ADHD itself as a risk marker for bipolar conversion in children with MDD. But they say that their work "expands on the extant literature by identifying additional, compounding risk factors that may more precisely predict switching in this population."
There were 24 children who converted to bipolar I disorder during follow-up and 79 who did not. Only seven children had subthreshold bipolar disorder symptoms at baseline, but 57% of these converted to a full diagnosis, compared with 21% of those without such symptoms. This gave a 9.57-fold increased risk for conversion, after accounting for age, gender, and emotional dysregulation.
"Taken together, past and current findings emphasize the critical importance of attending to subsyndromal manifestations of [bipolar I] disorder in children with MDD when making therapeutic decisions, especially given the potential risk for manic activations when treated with antidepressants," write Biederman et al in the Journal of Affective Disorders.
Emotional dysregulation, as ascertained using the Child Behavior Checklist, was itself associated with a 2.66-fold increased conversion risk, after adjustment for age, gender, and subthreshold bipolar symptoms. Both deficient emotional self-regulation and severe emotional dysregulation increased the risk for bipolar I disorder conversion, although only the former, less severe subtype was significant. The team attributes this to the sample size; just 22 children had severe emotional dysregulation at baseline.
"Clinicians should consider subthreshold bipolar disorder and emotional dysregulation in conjunction with previously identified risk factors of switching when evaluating, treating, and monitoring youth with ADHD and comorbid MDD," conclude the researchers.
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