White matter changes in paediatric bipolar disorder: A systematic review of diffusion magnetic resonance imaging studies.

Abstract

Background: Paediatric bipolar disorder (PBD) is characterized by severe mood fluctuations that deviate from typical childhood emotional development. Despite the efforts, the pathophysiology of this disorder is not well understood yet. In this review, we aimed to synthesize existing diffusion magnetic resonance imaging (dMRI) research findings focused on PBD.

Methods: A literature search was conducted using PubMed, Embase, Scopus, and Web of Science databases to identify relevant studies published before April 2024.

Results: A total of 23 studies met the inclusion criteria and were included in the review. The findings showed variations in fractional anisotropy (FA), axial diffusivity, radial diffusivity, and apparent diffusion coefficient in PBD patients compared to healthy controls (HC). Key findings included decreased FA in the anterior cingulate, anterior corona radiata, and corpus callosum, whose subregion, namely the genu of corpus callosum, was found to be correlated with clinical symptoms. Furthermore, longitudinal studies emphasized the significance of the uncinate fasciculus as having atypical developmental trajectories in PBD patients. In addition, graph analysis revealed widespread changes in structural connectivity, especially affecting the orbitofrontal cortex, frontal gyrus and basal ganglia. Lastly, machine learning models showed promising results in differentiating PBD from HC.

Limitations: Cross-sectional studies, small sample sizes, and different imaging protocols preclude integration of findings.

Conclusion: PBD shows to be associated with widespread structural changes compared to HC. Since these changes might be accountable for the clinical manifestations of this disorder, increase our understanding on the neurobiological underpinnings of PBD may help the identification of more effective treatments.