Electroconvulsive therapy and risk of dementia in patients with affective disorders: a cohort study

Background Electroconvulsive therapy (ECT) is the most effective treatment for severe episodes of mood disorders. Temporary memory loss is a common side-effect, but ongoing discussions exist regarding potential long-term adverse cognitive outcomes. Only a few studies have examined the frequency of dementia in patients after ECT. The aim of this study was to examine the association between ECT and risk of subsequent dementia in patients with a first-time hospital diagnosis of affective disorder. Methods We did a cohort study of patients aged 10 years and older in Denmark with a first-time hospital contact for an affective disorder from Jan 1, 2005, through Dec 31, 2015, identified in the Danish National Patient Registry with ICD-10 codes F30.0 to F39.9. From the registry we retrieved information on all ECTs registered for patients and followed up patients for incidental dementia (defined by hospital discharge diagnoses or acetylcholinesterase inhibitor use) until Oct 31, 2016. We examined the association between ECT and dementia using Cox regression analyses with multiple adjustments and propensity-score matching on sociodemographic and clinical variables. Findings Of 168 015 patients included in the study, 5901 (3.5%) patients had at least one ECT. During the median follow-up of 4.9 years (IQR 2.4-7.8) and 872 874 person years, the number of patients who developed dementia was 111 (0.1%) of 99 045 patients aged 10-49 years, 965 (2.7%) of 35 945 aged 50-69 years, and 4128 (12.5%) of 33 025 aged 70-108 years. 217 (3.6%) of the 5901 patients treated with ECT developed dementia, whereas of 162 114 patients not treated with ECT 4987 (3.1%) developed dementia. The corresponding incidences were 70.4 cases per 10 000 person-years (95% CI 61.6-80.5) and 59.2 per 10 000 person-years (57.6-60.8). In patients younger than 50 years and 50-69 years, ECT was not associated with a risk of dementia compared with age-matched patients who were not given ECT (age-adjusted hazard ratio [HR] 1.51, 95% CI 0.67-3.46, p=0.32; and 1.15, 0.91-1.47, p=0.22, respectively). In patients aged 70 years and older, ECT was associated with a decreased rate of dementia (0.68, 95% CI 0.58-0.80; p<0.0001), but in the propensity-score matched sample the HR was attenuated (0.77, 0.59-1.00; p=0.062). 31 754 patients (17.6%) died during follow-up (mortality rate per 1000 person-years 35.7, 95% CI 35.3-36.2) and supplementary analyses suggested that the risk of dementia, taking the competing mortality risk into account, was not significantly associated with ECT (subdistribution HR 0.98, 95% CI 0.76-1.26; p=0.24). Interpretation ECT was not associated with risk of incidental dementia in patients with affective disorders after correcting for the potential effect of patient selection or competing mortality. The findings from this study support the continued use of ECT in patients with severe episodes of mood disorders, including those who are elderly.