Why do some people with bipolar disorder and major depressive disorder (MDD) struggle with cognitive dysfunction, while others don’t? That is a focal point for Brigham and Women’s Hospital (BWH) researcher Katherine Burdick, PhD, within the Department of Psychiatry and director of the Mood and Psychosis Research Program, who is looking to identify predictors of outcome including inherited risk, aging, clinical factors, and long-term effects of recurrent illness.
Focusing on cognitive heterogeneity in bipolar disorder, Dr. Burdick has identified three cognitive subgroups: globally impaired, selectively impaired, and cognitively intact. In a recent study of people with bipolar disorder and their unaffected siblings, Dr. Burdick – a corresponding author – and colleagues found that genetic risk for bipolar disorder contributed more substantially to cognitive outcome in the globally impaired cluster than in the other subgroups.
“This also suggests that the developmental trajectory of cognitive change may differ by subgroup, a concept that requires longitudinal studies to confirm,” says Dr. Burdick. The research was published in the December 17, 2017 issue of Psychological Medicine.
“Cognitive deficits present in most patients with bipolar disorder and a smaller number with MDD. They are important because they significantly affect daily function and are not addressed by treatments for the disease itself,” notes Dr. Burdick. “These deficits can also interfere with treatment, resulting in difficulties remembering to take medications regularly or failing to show up for appointments.”
Dr. Burdick says additional implications for older adults with bipolar disorder and MDD — particularly because in patients with bipolar disorder, the development of cognitive impairment can mimic a neurodegenerative process.
“But we think the cognitive decline is more closely tied to the repeated episodes of mania and depression than to the aging process itself. What looks like dementia over time might be inflammation or cell loss,” she says, due to the cumulative effects of depressive illness. Planned longitudinal studies of the cognitive trajectory in people with bipolar disorder will also investigate whether the DNA ages more rapidly in patients.
Current Research Being Conducted by the Women’s Brain Initiative
Through support from the Women’s Brain Initiative at BWH, Dr. Burdick is also studying recurrent MDD in postmenopausal women – including how a lifetime history of depression, aging, and hormonal changes of menopause adversely affect cognitive function in these women.
“A better understanding of why some women with depression develop significant cognitive difficulties while others do not is critical for optimizing treatments to target quality of life and functional ability in postmenopausal women as they age,” says Dr. Burdick.