Hippocampal Volume and Cognitive Effects of ECT

Out on PubMed, from researchers in Glostrup, Denmark, is this study:

Hippocampal Volume and Memory Impairment after Electroconvulsive Therapy in Patients with Depression.

Gbyl K, Støttrup MM, Mitta Raghava J, Song XJ, Videbech P.Acta Psychiatr Scand. 2020 Nov 29. doi: 10.1111/acps.13259. Online ahead of print.PMID: 33251575

The abstract is copied below:

Objective: Patients hesitate to consent to Electroconvulsive Therapy (ECT) because of the fear of memory impairment. The mechanisms underlying this impairment are unclear, but several observations suggest hippocampal alterations may be involved. We investigated whether ECT-induced change in hippocampal volume correlates with memory impairment.

Methods: Using a 3T MRI-scanner, we acquired brain images and assessed cognitive performance in 22 severely depressed patients at three time-points: (1) before ECT series, (2) within one week after the series, and (3) at six-month follow-up. The hippocampus was segmented into subregions using Freesurfer. The dentate gyri (DG) were the primary regions of interest (ROIs) and major hippocampal subregions secondary ROIs. Cognitive performance was assessed using the Screen for Cognitive Impairment in Psychiatry and verbal memory using the Verbal Learning subtest. The linear mixed model and the repeated measures correlation were used for statistical analyses.

Results: ECT induced an increase in the right and left DG volume with co-occurring worsening in verbal memory, and these changes were negatively correlated (right DG, rrm =-.85, df=18, p=.0000002; left DG, rrm =-.58, df=18, p=.008). At a six-month follow-up, the volume of both DG decreased with a co-occurring improvement in verbal memory, and these changes were negatively correlated in the right DG (rrm =-.64, df=15, p=.005). Volume increases in 14 secondary ROIs were also negatively correlated with memory impairment.

Conclusion: ECT-related transient increases in the volume of major hippocampal subregions are associated with memory impairment. Hippocampal alterations following ECT should be the focus in searching for causes of the cognitive side-effects.

Keywords: Cognitive impairment; Depression; ECT; Hippocampus; Magnetic Resonance Imaging.

And from the text:

The main strength is that the study investigates the relationship between cognitive side effects and the volume of distinct hippocampal subregions, i.e., not only the whole hippocampus volume. Moreover, we report for the first time that the decrease in hippocampal volume during the follow up is related to cognitive performance improvement. Furthermore, the study used repeated measures correlation, an advantageous statistical approach in study design with repeated measurements. Finally, this is one of the first ECT studies assessing depressed patients with an objective, cognitive assessment tool designed to detect cognitive impairment in depression. The Danish version is, in addition, validated with well-established neuropsychological tests. Other studies typically use tests designed to detect dementia, such as the Montreal Cognitive Assessment or Mini-Mental Status Examination. The authors suggest using SCIP not only for research purposes but also to monitor cognitive performance in patients treated with ECT in clinical practice as SCIP is a bedside screening tool that only takes about 18 minutes to administer.

Some limitations must be addressed. Firstly, the sample size is small, which gives rise to type II errors. Therefore, we cannot exclude that we have overlooked important effects of ECT. Secondly, the study lacks a control group, making it difficult to differentiate between ECT effects and the effects of time, medication, and depression. Thirdly, due to ethical reasons, the patients continued psychopharmacological treatment during the entire study, which might influence the outcomes. However, the medication doses did not change significantly throughout the study. Fourthly, due to the naturalistic design, the patients received a different number of ECT-sessions in the series. A higher number of sessions could have had a stronger impact on both the cognitive and volumetric outcomes, but we did not find such associations in our sample. 

 To conclude, the ECT-induced transient increase in the volume of several hippocampal subregions is associated with transient impairment in objective cognitive performance, especially in delayed verbal memory. Further research should focus on the hippocampus in searching for mechanisms underlying the cognitive side effects of ECT. If the results are replicated, the new knowledge can lead to an ECT stimulation with a balanced affection of the hippocampus, reducing the cognitive side effects. 

 

This is a high quality study from a group of sophisticated researchers. The results expand their previously reported findings of association of antidepressant effects and hippocampal subregions, and widespread, transient cortical thickness increases with ECT.

Understanding, and limiting, cognitive effects of ECT is important, but it cannot be the tail that wags the dog. The transient nature of the cognitive effects of ECT should not be forgotten (pun intended); efficacy for urgent, severe psychiatric illness is what sets ECT apart from all other treatments and should be the driver in clinical decision-making.

Understanding the cause of cognitive side effects will likely lead to forms of ECT with improved tolerability- this research should proceed pari passu with ongoing prescription of proven ECT techniques appropriate for the urgency of the clinical situation. 

A very interesting sidebar in this paper is the use of the Screen for Cognitive Impairment in Psychiatry (SCIP), an assessment tool that is not widely discussed. The authors' suggestion that it be used more frequently in clinical ECT practice is worth considering.