Volume Increase of the Hippocampus after Electroconvulsive Therapy - The Role of the Electric Field and the Individual Differences due to Body Mass Index, Sex and Age

Abstract

Electroconvulsive therapy (ECT) involves passing an electrical current through the brain, intentionally causing a brief seizure. In Norway, it is common to calculate the dose according to an age-based method. Recent studies have shown that ECT induced volume changes in the grey matter areas, hippocampus and amygdala, strongly correlate with the strength of the electric field (EF). There is not yet a complete understanding of how EFs interact with the brain. This thesis aims to evaluate how well the age-based method accounts for individual differences and investigate the effect of ECT by estimating potential volume changes of the hippocampi resulting from the treatment combined with simulations of the EFs generated by the ECT stimulus. This project is a part of the ongoing research in the ECT-MRI group at Mohn Medical Imaging and Visualization Centre (MMIV). To examine the longitudinal volume changes, T1-weighted magnetic resonance imaging (MRI) scans from 29 patients scanned once before and once after a series of right unilateral ECT were analysed. Variations between individuals were further characterised in regard to body mass index (BMI), sex and age, to examine the extent to which the treatment strategies used today take into account individual differences. Statistically significant negative correlation values were found between the EF strength in the hippocampi and BMI and age. However, there were no significant relationships between volume change and the variables BMI and age. Furthermore, significantly higher EF strengths in the hippocampi were found in female patients compared to male patients. Corresponding significantly greater volume changes in the left hippocampus were found for female patients. Young women have also been reported to be at higher risk for side effects. Moreover, the relationship between volume change and EF strength reported in previous studies was confirmed. In summary, the results in this thesis show that the age-based method used in the clinic today does not correct for individual differences in a way that ensures equal effects of the ECT treatment.