Risk of suicide and accidental deaths among elderly patients with cognitive impairment

Background: The leading causes of death among the elderly with cognitive impairment are unknown. This study aims to estimate the suicide and accidental death rates on the basis of a clinical case registry of patients diagnosed with cognitive impairment. Methods: The target sample consisted of 10,169 patients diagnosed with dementia or mild cognitive impairment (MCI), who were evaluated at the Clinical Research Center for Dementia of Korea (CREDOS) from January 2005 to December 2013. Information about whether the patients had died from suicide or in any kind of accident by December 31, 2016, was obtained from the database of the National Statistical Office (NSO). The standardized mortality ratio (SMR) and Cox-regression analysis were performed for evaluating the risk of suicide and accidental death as identified by the ICD-10. Results: The average of the Clinical Dementia Rating Scale (CDR) score (0.68 vs 0.93) was lower, and the age at the time of study registration (71.42 vs 75.68 years) was younger in the suicidal death group, as compared to the accidental death group. The overall SMR for accidental death in cognitively impaired patients (1.44, 95% CI 1.22-1.71) was significantly higher than the general population. Later onset (1.43, 95% CI 1.20-1.71) and older age (2.21, 95% CI 1.04-4.68) increased the risk of accidental death in cognitively impaired patients. According to the dementia subtypes, the SMR for accidental death was higher in both Alzheimer's disease (1.72, 95% CI 1.36-2.14) and vascular dementia (2.14, 95% CI 1.27-3.38). Additionally, the SMR for accidental death showed an increasing tendency as the CDR score increased (mild 1.80, 95% CI 1.32-2.42, moderate 1.86, 95% CI 1.07-3.03, severe 3.32, 95% CI 1.08-7.76). Unemployment increased the risks of both suicide (3.71, 95% CI 1.54-8.95) and accidental death (2.09, 95% CI 1.20-3.63). Conclusions: Among people with cognitive impairment, the risk of death by suicide did not increase, whereas that of accidental death increased significantly. Preventive strategies for premature mortality in those with cognitive impairment should be implemented from the early stages and should include careful evaluation of the individual risk factors for each type of death.