WHITE MATTER INTEGRITY IN EUTHYMIC BIPOLAR I PATIENTS RELEVANCE TO COGNITIVE FUNCTIONS

Abstract

Bipolar Disorder (BD) is a chronic, debilitating illness with a lifetime worldwide prevalence of 4.8% and more disability-adjusted life-years lost than major neurological conditions or cancer as it causes severe suffering for patients and caregivers, and constitute a major health economic challenge for societies(Gustavsson et al., 2011). According to WHO global burden of disease study, BD rank within the top 20 causes of disability among all medical conditions worldwide, and rank 6th among the mental disorders(Vos et al., 2012). Patients with bipolar disorder seem to be the most costly in terms of overall medical and psychological care in comparison to other mental patients and one of the most costly categories of patients in the whole field of medicine.(Fountoulakis, 2015) Although the last few decades, there are available efficacious treatments for Bipolar disorder; often syndromal or symptomatic recovery does not go together with functional recovery. This means that in spite of the fact that patients recover in clinical terms, frequently they do not return to their functioning level as it was before getting ill(Fountoulakis, 2015). In the clinical setting, many bipolar disorder patients do complain of persistent difficulties in concentration, memory, inability to perform optimally in challenging tasks or even, in day to day functioning. While a variety of factors may be responsible for persistent functional impairments, at least subgroups of patients are likely to experience poor psychosocial outcomes as a result of cognitive dysfunction (Aran et al., 2004; Vaidya et al., 1998 (. Several studies indicate that as many as 60% of BD patients are cognitively impaired at a level deemed to be clinically relevant during periods of affectiveremission (Martino et al., 2008 ( Euthymic bipolar disorder patients show limitations in a number of cognitive domains especially executive functions, declarative memory, and sustained attention .This seems to be a cause for a continuous impairment in social and occupational functioning in a large number of patients(Delgado et al., 2012). Neurocognitive symptoms are not only important because they tell us about the brain areas and functions involved in the pathogenesis of the disease and represent potential endophenotypes, but also for their clinical value; there is an ongoing debate on to what extent they should be included in the diagnostic criteria for schizophrenia and bipolar disorder(Delgado et al., 2012). Despite being a common and significant illness, the neurophysiologic basis of BD was relatively little studied until the advent of advanced neuroimaging techniques, primarily magnetic resonance imaging tech¬nologies, allowed in vivo noninvasive examination of the human brain. Consequently, neuroimaging studies of BD prolif-erated in the past decade(Savetz et al., 2013). Evaluating white matter of the brain (WM) structure appears to be a promising area of investigation for understanding the potential for altered connectivity between brain regions believed to contribute to bipolar disorder symptomatology. White matter alterations may be responsible for some of the functional activation deficits found in patients with bipolar disorder. Several hypotheses regarding WM abnormalities in bipolar disorder have been suggested(Mahon et al., 2010; Benedetti et al., 2011).