A clinical and neurocognitive study of recurrent depression and bipolar spectrum disorder in young adults

Abstract

The presentation and neurobiology of depression in young adults is an important but understudied area of psychiatric research. Many young adults with early-onset recurrent major depressive disorder (MDD) have a strong genetic loading for mood disorder and, in the longer term, may be at high risk of developing bipolar affective disorder (BPAD). The objectives of this thesis were two-fold: firstly, to assess the prevalence and clinical validity of bipolar spectrum disorder (BSD) in a consecutive sample of young adults with recurrent depression; and secondly, to carry out a neurocognitive study comparing clinically recovered (euthymic) young adults with recurrent MDD, euthymic BSD patients and well-matched controls. Eighty-seven young adults presenting with recurrent depression were recruited from consecutive referrals to a psychiatric clinic at a University Health Service. Of these, 14 had BPAD, 27 had BSD and 46 had recurrent MDD. The classic criteria used to assess the validity of psychiatric diagnoses (namely, clinical phenomenology, clinical course, family history and treatment response) were applied to the BSD group of patients. This provided only modest support for the validity of the BSD criteria according to clinical parameters. However, on neurocognitive testing, there were significant differences between BSD patients, MDD patients and controls in terms of performance on tests of attention, executive function and declarative memory. This finding suggested that the diagnsotic criteria for BSD were able to identify a sub-group of young adults with recurrent depression and strong bipolar features (such as a family history of bipolar disorder or a personal history of antidepressantassociated hypomania) who performed less well than young adults with more straightforward unipolar depression on tests of prefrontal and hippocampal functioning. The implications of these findings for the concept of bipolar spectrum disorder, and for our understanding of the neuropsychology of mood disorders, are discussed. Limitations of this work and directions for future research are also considered.