Relationship of subjective and objective measures of cognitive impairment post-ECT

Autobiographical memory impairment is an important side-effect of ECT, and is perceived as persistent by some patients.^{Reference Koopowitz and Chur-Hansen3} The majority of contemporary ECT studies have used the Colombia University Autobiographical Memory Interview (CUAMI) or its shorter form (CUAMI-SF) as an objective measure of this. The relationship between objective and subjective assessment of autobiographical memory impairment has been studied. Brakemeier et al^{Reference Brakemeier, Berman, Prudic, Zwillenberg and Sackeim4} demonstrated that longer and more detailed scales measuring subjective memory impairment (Cognitive Failures Questionnaire and Subjective Memory Complaints Questionnaire) did not correlate well with the CUAMI. However, there was a high level of correlation between the CUAMI and the GSE of Memory (one of the questionnaires used by Sigström et al).^{Reference Brakemeier, Berman, Prudic, Zwillenberg and Sackeim4} The GSE of Memory consists of two simple questions where patients are asked to rate their expectations about the likely effect of ECT on their memory prior to treatment, and post-ECT to evaluate the overall effect that it has had on memory. This is similar to the common clinical practice of assessing patients’ memory by asking them about it directly. The correlation between this simple scale and a more detailed assessment of autobiographical memory indicates that patient experience of cognitive impairment may be more important, and closer to objective measures of memory, than is sometimes suggested. It also suggests that the data presented by Sigström et al, particularly using the GSE of Memory, may relate both to subjective and objective memory difficulties.

Limitations of the data

There are several caveats to the findings presented in this study. Missing data has been a difficult issue in ECT research, with many studies reporting around a 50% drop-out rate.^{Reference Sackeim, Prudic, Fuller, Keilp, Lavori and Olfson2}

Similarly, in this study approximately 48% of participants were not able to be included in the final analysis, the majority because of a lack of post-ECT data regarding memory measures. One important possibility is that patients with more significant cognitive or memory impairment may be less likely to undertake further assessment, leading to an underestimate of the effect of ECT on memory. Similarly, patients with more severe depressive symptoms may be less likely to engage in ongoing testing, and may have more ongoing cognitive symptoms, including memory impairment, than those who experience an improvement in these symptoms with ECT.

Clinical features may also contribute to the presence of subjective memory impairment following ECT. For instance, patients with more severe depressive symptoms may be at higher risk of having or developing cognitive impairment. They may also be more likely to undergo ECT. This makes delineating the effects of ECT on cognition difficult. Similarly, the negativity typically associated with more severe depression may have led participants to report more negative expectations of treatment. It would have been helpful to measure depression severity and in future research this could be controlled for. Data were not presented on the correlations between the GSE of Memory and the GSE of Mood, which would have assisted in examining these potential associations.

In addition to clinical factors, there is some evidence that rates of memory difficulties following ECT may depend on the assessor and location of testing. Lower rates of subjective memory impairment have been reported in studies where medical assessors in clinical settings were used.^{Reference Rose, Wykes, Leese, Bindman and Fleischmann5} In the current study, pre-ECT subjective memory was assessed in person, while post-ECT effects were measured over the phone. This may have had some impact on how participants responded to questions regarding subjective memory, and as such the responses given post-ECT may have been more negative, and possibly more realistic, than those given in person prior to treatment.

Clinical implications

Despite the limitations and the subjective nature of the assessments, this data provides important information regarding which patients are more likely to experience memory impairment following ECT. In particular, subjective memory worsening was associated with more negative expectations of the likely memory effects of ECT before treatment, something that could potentially be modified. Interestingly, patients’ expectations of mood effects of ECT were not associated with negative effects on memory. This suggests that the finding of an association between negative expectations of ECT and subjective memory impairment does not relate to a general negative attitude towards ECT. A number of factors may have an impact on patients’ attitudes and expectations about treatment with ECT, including the manner in which ECT is discussed.

There is some suggestion that attempting to downplay the cognitive side-effects of ECT may be unhelpful, and can invalidate patients’ experience of subjective cognitive impairment.^{Reference Vamos6} On the other hand, a discussion where cognitive side-effects are highlighted as likely to occur may increase the chances that patients expect, and possibly develop memory impairment. The consent process presents an opportunity for clinicians to modify patients' expectations of ECT, its effects and potential side-effects. A balanced discussion, that acknowledges but does not minimise side-effects, may benefit subjective memory outcomes.

Overall, this prospective study provides some reassurance regarding the longer-term memory effects of ECT, with only a small proportion (16.2%) of patients found to have worsening in subjective memory compared with prior to ECT. It adds to the growing literature regarding the importance of subjective memory impairment after ECT, and we suggest that measurement of subjective memory should be a routine part of treatment and follow-up. The intriguing finding that those patients who anticipated negative effects of ECT on memory were more likely to have higher rates of subjective memory impairment at follow-up indicates that further research into identifying these patients is required. It also implies that subjective memory impairment after ECT may be modifiable, possibly by addressing negative expectations prior to treatment, or by adjusting the way in which ECT is discussed with patients. In future, it would be of interest to trial a specific education or a consistent informed consent process, to determine whether this has a positive impact on subjective memory impairment and its associated distress. In the meantime, we suggest that clinicians take a balanced approach to discussing the possible memory effects of ECT with patients. By exploring their patients’ expectations and understanding of ECT, and addressing negative expectations prior to treatment, there may be an opportunity for clinicians to modify their subjective memory outcomes.