Mood episodes are associated with increased cortical thinning: A longitudinal study of bipolar disorder type II

Abstract

| INTRODUC TI ONBipolar disorder (BD) is a chronic psychiatric illness characterized by episodic disturbances in mood and activity levels and affects 2%-3% of the population worldwide. 1 BD type I is defined by at least one manic episode, while BD type II is characterized by alternating episodes of hypomania and depression. The clinical significance of both subtypes is comparable in terms of illness burden, role impairments, AbstractObjectives: Previous studies found evidence for thinner frontotemporal cortices in bipolar disorder (BD), yet whether this represents a stable disease trait or an effect of mood episodes remains unknown. Here, we assessed the reproducibility of thinner frontotemporal cortices in BD type II, compared longitudinal changes in cortical thickness between individuals with BD type II and healthy controls (HCs), and examined the effect of mood episodes on cortical thickness change.Methods: Thirty-three HCs and 29 individuals with BD type II underwent 3T magnetic resonance imaging at baseline, as published previously, and 2.4 years later, at follow-up. Cross-sectional and longitudinal analyses of cortical thickness were performed using Freesurfer, and relationships with mood episodes from baseline to follow-up were assessed.Results: Individuals with BD type II had thinner left and right prefrontal and left temporal cortex clusters at follow-up (all corrected P < 0.001), consistent with baseline results. Both groups showed widespread longitudinal cortical thinning, and patients had increased thinning in a left temporal cortex cluster compared to HCs (corrected P < 0.001). Patients with more (>2) depressive episodes between baseline and followup had greater left temporal cortical thinning than patients with fewer depressive episodes (corrected P < 0.05). In addition, patients with more depressive episodes had greater thinning in bilateral ventromedial prefrontal clusters relative to HCs (uncorrected P < 0.05), yet these results did not survive correction for multiple comparisons. Conclusions:Together, these findings support reduced frontotemporal cortical thickness in BD type II and provide the first preliminary evidence for an association between depressive episodes and increased cortical thinning. K E Y W O R D Sbipolar disorder, cortical thickness, cortical thinning, depressive episodes, longitudinal study, progressive changes

Baseline long‐term potentiation‐like cortical plasticity is associated with longitudinal cortical thinning in healthy adults and in adults with bipolar disorder type II

“…Participants had widespread bilateral cortical thinning from baseline to follow‐up ( p FWER < .05; Figure 2a–c; see Figure S2 for uncorrected maps and maps with an annualized rate of cortical thickness change), and there was no significant group difference in the rate of cortical thickness change after correction for analyses across the brain. However, uncorrected results indicated that patients had a steeper rate of cortical thinning than healthy individuals in bilateral temporal and ventromedial prefrontal cortices (Figure 2d), consistent with findings from the larger sample (Zak et al, 2019).…”

“…Thinning of the cerebral cortex occurs as part of healthy aging across adulthood and might be accelerated in many psychiatric disorders, including bipolar disorder (BPD) types I and II (Fjell & Walhovd, 2010;Hibar et al, 2018;Rimol et al, 2010;Schmaal et al, 2016;Zak et al, 2019). However, the precise neurobiological mechanisms underlying longitudinal cortical thickness changes and their functional implications in healthy aging and in disease development and progression remain to be clarified.…”

“…A common psychiatric disorder associated with reduced cortical thickness and accelerated cortical thinning is BPD type II (Zak et al, 2019(Zak et al, , 2018. BPD type II is highly prevalent among patients with recurrent depressive episodes and has a clinical significance comparable to BPD type I in terms of depressive symptom severity, social and occupational impairments, and suicide attempts (Merikangas et al, 2011).…”

“…To our knowledge, no previous studies have investigated the relationship between an in vivo correlation of synaptic function and plasticity and longitudinal cortical thickness changes in healthy adults or in individuals with a psychiatric disorder associated with accelerated thinning of the cortex. We have previously reported impaired VEP plasticity and an increased cortical thinning rate in adults with BPD type II compared with healthy adults (Zak et al, 2019(Zak et al, , 2018. In the present work, we included a subsample from the previously published studies comprising 15 adults with BPD type II and 32 healthy adults who completed measurements of VEP plasticity and magnetic resonance imaging (MRI) of the brain at baseline and a follow-up brain MRI, on average 2.3 years later.…”

Common and Specific Characteristics of Adolescent Bipolar Disorder Types I and II: A Combined Cortical Thickness and Structural Covariance Analysis

“…This result is similar to a longitudinal study focused on adult BD-II patients. This study observed that adult BD-II patients with more depressive number of episodes between baseline and follow-up periods had more severe thinning of the left temporal cortex than patients with fewer depressive numbers of episodes (76). Hence, our finding further supported the association between increased cortical thinning and the number of mood episodes.…”